| 1. |
- Aase-Remedios, Madeleine E., et al.
(författare)
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Evolution of the Spider Homeobox Gene Repertoire by Tandem and Whole Genome Duplication
- 2023
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Ingår i: Molecular biology and evolution. - : Oxford University Press. - 0737-4038 .- 1537-1719. ; 40:12
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Tidskriftsartikel (refereegranskat)abstract
- Gene duplication generates new genetic material that can contribute to the evolution of gene regulatory networks and phenotypes. Duplicated genes can undergo subfunctionalization to partition ancestral functions and/or neofunctionalization to assume a new function. We previously found there had been a whole genome duplication (WGD) in an ancestor of arachnopulmonates, the lineage including spiders and scorpions but excluding other arachnids like mites, ticks, and harvestmen. This WGD was evidenced by many duplicated homeobox genes, including two Hox clusters, in spiders. However, it was unclear which homeobox paralogues originated by WGD versus smaller-scale events such as tandem duplications. Understanding this is a key to determining the contribution of the WGD to arachnopulmonate genome evolution. Here we characterized the distribution of duplicated homeobox genes across eight chromosome-level spider genomes. We found that most duplicated homeobox genes in spiders are consistent with an origin by WGD. We also found two copies of conserved homeobox gene clusters, including the Hox, NK, HRO, Irx, and SINE clusters, in all eight species. Consistently, we observed one copy of each cluster was degenerated in terms of gene content and organization while the other remained more intact. Focussing on the NK cluster, we found evidence for regulatory subfunctionalization between the duplicated NK genes in the spider Parasteatoda tepidariorum compared to their single-copy orthologues in the harvestman Phalangium opilio. Our study provides new insights into the relative contributions of multiple modes of duplication to the homeobox gene repertoire during the evolution of spiders and the function of NK genes.
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| 2. |
- Budd, Graham, et al.
(författare)
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Comment on "The lower Cambrian lobopodian Cardiodictyon resolves the origin of euarthropod brains"
- 2023
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Ingår i: Science. - : American Association for the Advancement of Science (AAAS). - 0036-8075 .- 1095-9203. ; 380:6652
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Tidskriftsartikel (refereegranskat)abstract
- Strausfeld et al. (Report, 24 Nov 2022, p. 905) claim that Cambrian fossilized nervous tissue supports the interpretation that the ancestral panarthropod brain was tripartite and unsegmented. We argue that this conclusion is unsupported, and developmental data from living onychophorans contradict it.
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| 3. |
- Damen, Wim, et al.
(författare)
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Embryonic development and the understanding of the adult body plan in myriapods
- 2009
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Ingår i: Soil Organisms. - 1864-6417. ; 81:3, s. 337-346
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Tidskriftsartikel (refereegranskat)abstract
- The adult body plan is laid down during embryonic and post-embryonic development of an organism. Here we review two examples for how data on gene expression during embryonic development have changed our understanding of the adult body plan of myriapods. Gene expression studies in the geophilomorph centipede Strigamia maritima (Leach, 1817) have demonstrated that a developmental constraint underlies the always-odd number of leg bearing segments in geophilomorph centipedes. Similarly, data on gene expression in the millipede Glomeris marginata (Villers, 1789) have demonstrated a decoupling of dorsal and ventral segmentation, which provided an explanation for the discrepancy in dorsal and ventral structures in the body of millipedes. Knowledge on the molecular mechanisms underlying embryonic development therefore significantly contributes to understanding morphological features of the adult myriapod body.
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| 4. |
- Damen, Wim, et al.
(författare)
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Pair rule gene orthologs in spider segmentation
- 2005
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Ingår i: Evolution & Development. - 1520-541X .- 1525-142X. ; 7:6, s. 618-628
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Tidskriftsartikel (refereegranskat)abstract
- The activation of pair rule genes is the first indication of the metameric organization of the Drosophila embryo and thus forms a key step in the segmentation process. There are two classes of pair rule genes in Drosophila: the primary pair rule genes that are directly activated by the maternal and gap genes and the secondary pair rule genes that rely on input from the primary pair rule genes. Here we analyze orthologs of Drosophila primary and secondary pair rule orthologs in the spider Cupiennius salei. The expression patterns of the spider pair rule gene orthologs can be subdivided in three groups: even-skipped and runt-1 expression is in stripes that start at the posterior end of the growth zone and their expression ends before the stripes reach the anterior end of the growth zone, while hairy and pairberry-3 stripes also start at the posterior end, but do not cease in the anterior growth zone. Stripes of odd-paired, odd-skipped-related-1, and sloppy paired are only found in the anterior portion of the growth zone. The various genes thus seem to be active during different phases of segment specification. It is notable that the spider orthologs of the Drosophila primary pair rule genes are active more posterior in the growth zone and thus during earlier phases of segment specification than most orthologs of Drosophila secondary pair rule genes, indicating that parts of the hierarchy might be conserved between flies and spiders. The spider ortholog of the Drosophila pair rule gene fushi tarazu is not expressed in the growth zone, but is expressed in a Hox-like fashion. The segmentation function of fushi tarazu thus appears to be a newly acquired role of the gene in the lineage of the mandibulate arthropods.PMID:16336415
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| 5. |
- Eriksson, Bo Joakim, et al.
(författare)
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Head patterning and Hox gene expression in an onychophoran and its implications for the arthropod head problem
- 2010
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Ingår i: Development, Genes and Evolution. - : Springer Science and Business Media LLC. - 0949-944X .- 1432-041X. ; 220:3-4, s. 117-122
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Tidskriftsartikel (refereegranskat)abstract
- The arthropod head problem has puzzled zoologists for more than a century. The head of adult arthropods is a complex structure resulting from the modification, fusion and migration of an uncertain number of segments. In contrast, onychophorans, which are the probable sister group to the arthropods, have a rather simple head comprising three segments that are well defined during development, and give rise to the adult head with three pairs of appendages specialised for sensory and food capture/manipulative purposes. Based on the expression pattern of the anterior Hox genes labial, proboscipedia, Hox3 and Deformed, we show that the third of these onychophoran segments, bearing the slime papillae, can be correlated to the tritocerebrum, the most anterior Hox-expressing arthropod segment. This implies that both the onychophoran antennae and jaws are derived from a more anterior, Hox-free region corresponding to the proto and deutocerebrum of arthropods. Our data provide molecular support for the proposal that the onychophoran head possesses a well-developed appendage that corresponds to the anterior, apparently appendage-less region of the arthropod head.
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| 6. |
- Gasiorowski, Ludwik, et al.
(författare)
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Molecular evidence for a single origin of ultrafiltration-based excretory organs
- 2021
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Ingår i: Current Biology. - : Elsevier. - 0960-9822 .- 1879-0445. ; 31:16, s. 3629-
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Tidskriftsartikel (refereegranskat)abstract
- Excretion is an essential physiological process, carried out by all living organisms, regardless of their size or complexity.(1-3) Both protostomes (e.g., flies and flatworms) and deuterostomes (e.g., humans and sea urchins) possess specialized excretory organs serving that purpose, Those organs exhibit an astonishing diversity, ranging from units composed of just few distinct cells (e.g., protonephridia) to complex structures, built by millions of cells of multiple types with divergent morphology and function (e.g., vertebrate kidneys).(4,5) Although some molecular similarities between the development of kidneys of vertebrates and the regeneration of the protonephridia of flatworms have been reported, (6,7) the molecular underpinnings of the development of excretory organs have never been systematically studied in a comparative context. (4) Here, we show that a set of transcription factors (eya, six1/2, pou3, sail, Ihx1/5, and osr) and structural proteins (nephrin, kirre, and zo1) is expressed in the excretory organs of a phoronid, brachiopod, annelid, onychophoran, priapulid, and hemichordate that represent major protostome lineages and non-vertebrate deuterostomes. We demonstrate that the molecular similarity observed in the vertebrate kidney and flatworm protonephridia(6,7) is also seen in the developing excretory organs of those animals. Our results show that all types of ultrafiltration-based excretory organs are patterned by a conserved set of developmental genes, an observation that supports their homology. We propose that the last common ancestor of protostomes and deuterostomes already possessed an ultrafiltration-based organ that later gave rise to the vast diversity of extant excretory organs, including both proto- and metanephridia.
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| 7. |
- Harper, Amber, et al.
(författare)
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Widespread retention of ohnologs in key developmental gene families following whole-genome duplication in arachnopulmonates
- 2021
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Ingår i: G3. - : Oxford University Press. - 2160-1836. ; 11:12
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Tidskriftsartikel (refereegranskat)abstract
- Whole-genome duplications (WGDs) have occurred multiple times during animal evolution, including in lineages leading to vertebrates, teleosts, horseshoe crabs, and arachnopulmonates. These dramatic events initially produce a wealth of new genetic material, generally followed by extensive gene loss. It appears, however, that developmental genes such as homeobox genes, signaling pathway components and microRNAs are frequently retained as duplicates (so-called ohnologs) following WGD. These not only provide the best evidence for WGD, but an opportunity to study its evolutionary consequences. Although these genes are well studied in the context of vertebrate WGD, similar comparisons across the extant arachnopulmonate orders are patchy. We sequenced embryonic transcriptomes from two spider species and two amblypygid species and surveyed three important gene families, Hox, Wnt, and frizzled, across these and 12 existing transcriptomic and genomic resources for chelicerates. We report extensive retention of putative ohnologs, further supporting the ancestral arachnopulmonate WGD. We also found evidence of consistent evolutionary trajectories in Hox and Wnt gene repertoires across three of the six arachnopulmonate orders, with interorder variation in the retention of specific paralogs. We identified variation between major clades in spiders and are better able to reconstruct the chronology of gene duplications and losses in spiders, amblypygids, and scorpions. These insights shed light on the evolution of the developmental toolkit in arachnopulmonates, highlight the importance of the comparative approach within lineages, and provide substantial new transcriptomic data for future study.
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| 8. |
- Heingård, Miriam, et al.
(författare)
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FoxB, a new and highly conserved key factor in arthropod dorsal-ventral (DV) limb patterning
- 2019
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Ingår i: EvoDevo. - : BMC. - 2041-9139. ; 10
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Tidskriftsartikel (refereegranskat)abstract
- Forkhead box (Fox) transcription factors evolved early in animal evolution and represent important components of conserved gene regulatory networks (GRNs) during animal development. Most of the researches concerning Fox genes, however, are on vertebrates and only a relatively low number of studies investigate Fox gene function in invertebrates. In addition to this shortcoming, the focus of attention is often restricted to a few well-characterized Fox genes such as FoxA (forkhead), FoxC (crocodile) and FoxQ2. Although arthropods represent the largest and most diverse animal group, most other Fox genes have not been investigated in detail, not even in the arthropod model species Drosophila melanogaster. In a general gene expression pattern screen for panarthropod Fox genes including the red flour beetle Tribolium castaneum, the pill millipede Glomeris marginata, the common house spider Parasteatoda tepidariorum, and the velvet worm Euperipatoides kanangrensis, we identified a Fox gene with a highly conserved expression pattern along the ventral ectoderm of arthropod and onychophoran limbs. Functional investigation of FoxB in Parasteatoda reveals a hitherto unrecognized important function of FoxB upstream of wingless (wg) and decapentaplegic (dpp) in the GRN orchestrating dorsal-ventral limb patterning.
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| 9. |
- Heingård, Miriam, et al.
(författare)
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The forkhead box containing transcription factor FoxB is a potential component of dorsal-ventral body axis formation in the spider Parasteatoda tepidariorum
- 2020
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Ingår i: Development, Genes and Evolution. - : SPRINGER. - 0949-944X .- 1432-041X. ; 230:2, s. 65-73
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Tidskriftsartikel (refereegranskat)abstract
- In the spider, determination of the dorsal-ventral body (DV) axis depends on the interplay of the dorsal morphogen encoding gene decapentaplegic (Dpp) and its antagonist, short gastrulation (sog), a gene that is involved in the correct establishment of ventral tissues. Recent work demonstrated that the forkhead domain encoding gene FoxB is involved in dorsal-ventral axis formation in spider limbs. Here, Dpp likely acts as a dorsal morphogen, and FoxB is likely in control of ventral tissues as RNAi-mediated knockdown of FoxB causes dorsalization of the limbs. In this study, we present phenotypes of FoxB knockdown that demonstrate a function in the establishment of the DV body axis. Knockdown of FoxB function leads to embryos with partially duplicated median germ bands (Duplicitas media) that are possibly the result of ectopic activation of Dpp signalling. Another class of phenotypes is characterized by unnaturally slim (dorsal-ventrally compressed) germ bands in which ventral tissue is either not formed, or is specified incorrectly, likely a result of Dpp over-activity. These results suggest that FoxB functions as an antagonist of Dpp signalling during body axis patterning, similarly as it is the case in limb development. FoxB thus represents a general player in the establishment of dorsal-ventral structures during spider ontogeny.
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| 10. |
- Hogvall, Mattias, et al.
(författare)
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Analysis of the Wnt gene repertoire in an onychophoran provides new insights into the evolution of segmentation
- 2014
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Ingår i: EvoDevo. - : Springer Science and Business Media LLC. - 2041-9139. ; 5, s. 14-
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Tidskriftsartikel (refereegranskat)abstract
- Background: The Onychophora are a probable sister group to Arthropoda, one of the most intensively studied animal phyla from a developmental perspective. Pioneering work on the fruit fly Drosophila melanogaster and subsequent investigation of other arthropods has revealed important roles for Wnt genes during many developmental processes in these animals. Results: We screened the embryonic transcriptome of the onychophoran Euperipatoides kanangrensis and found that at least 11 Wnt genes are expressed during embryogenesis. These genes represent 11 of the 13 known subfamilies of Wnt genes. Conclusions: Many onychophoran Wnt genes are expressed in segment polarity gene-like patterns, suggesting a general role for these ligands during segment regionalization, as has been described in arthropods. During early stages of development, Wnt2, Wnt4, and Wnt5 are expressed in broad multiple segment-wide domains that are reminiscent of arthropod gap and Hox gene expression patterns, which suggests an early instructive role for Wnt genes during E. kanangrensis segmentation.
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| 11. |
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| 12. |
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| 13. |
- Hogvall, Mattias, et al.
(författare)
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Gene expression analysis of potential morphogen signalling modifying factors in Panarthropoda
- 2018
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Ingår i: EvoDevo. - : BMC. - 2041-9139. ; 9
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Tidskriftsartikel (refereegranskat)abstract
- Background: Morphogen signalling represents a key mechanism of developmental processes during animal development. Previously, several evolutionary conserved morphogen signalling pathways have been identified, and their players such as the morphogen receptors, morphogen modulating factors (MMFs) and the morphogens themselves have been studied. MMFs are factors that regulate morphogen distribution and activity. The interactions of MMFs with different morphogen signalling pathways such as Wnt signalling, Hedgehog (Hh) signalling and Decapentaplegic (Dpp) signalling are complex because some of the MMFs have been shown to interact with more than one signalling pathway, and depending on genetic context, to have different, biphasic or even opposing function. This complicates the interpretation of expression data and functional data of MMFs and may be one reason why data on MMFs in other arthropods than Drosophila are scarce or totally lacking.Results: As a first step to a better understanding of the potential roles of MMFs in arthropod development, we investigate here the embryonic expression patterns of division abnormally delayed (dally), dally-like protein (dlp), shifted (shf) and secreted frizzled-related protein 125 (sFRP125) and sFRP34 in the beetle Tribolium castaneum, the spider Parasteatoda tepidariorum, the millipede Glomeris marginata and the onychophoran Euperipatoides kanangrensis. This pioneer study represents the first comprehensive comparative data set of these genes in panarthropods.Conclusions: Expression profiles reveal a high degree of diversity, suggesting that MMFs may represent highly evolvable nodes in otherwise conserved gene regulatory networks. Conserved aspects of MMF expression, however, appear to concern function in segmentation and limb development, two of the key topics of evolutionary developmental research.
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| 14. |
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| 15. |
- Hogvall, Mattias, 1984-
(författare)
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Investigation of Hox gene expression and Wnt-signalling in basally branching ecdysozoans
- 2018
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- One of the most important processes in the development of an animal is the determination and patterning of the primary body axis, the anterior-posterior (AP) axis. After the AP axis has been established the embryo grows and elongates through posterior elongation.Several evolutionary conserved sets of genes and signalling pathways are involved in AP axis formation and posterior elongation, including Wnt-signalling. Wnt-signalling was involved in AP axis determination and posterior elongation even before the evolution of the Bilateria. In segmented animals, Wnt-signalling is also involved in maintaining segmental boundaries and in giving each segment its polarity. Hox genes, conversely, play a significant role in the regionalisation of the AP axis in Bilateria. This role as regionalisation factors probably emerged within the bilaterian in stem-group and it has been speculated that Wnt genes may have had this function prior to the rise of the Hox genes.The goal of this work is to shed light on the expression and function of Wnt-signalling and Hox gene patterning in basally branching ecdysozoans, Priapulida and Onychophora, two phyla that are underrepresented in current research, but represent key phyla for the understanding of ecdysozoan evolution.Wnt genes are likely to have retained a prominent function in posterior regionalisation and elongation in Priapulida. Investigation of Hox gene expression patterns proved to be difficult in Priapulida, but preliminary results suggest partially conserved function in AP axis patterning.In Onychophora, Wnt-signalling appears to be involved in segment formation, intrasegmental patterning and segment/parasegment border maintenance. Some of the onychophoran Wnt genes are expressed in Hox-like patterns suggesting a role in AP-axis patterning, a function that Wnt genes may thus have retained throughout their evolution.Finally, I have also investigated some of the factors involved in Wnt-signalling (or morphogen processing in general). These genes, the morphogen-interfering factors (MIFs), have been poorly investigated in general. I studied their expression in an onychophoran and a number of other emerging arthropod model organisms in order to obtain a more solid basis for comparison. These data, although difficult to interpret, suggest that the interaction of Wnts and MIFs is diverse and complex among Panarthropoda.
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| 16. |
- Högvall, Mattias, et al.
(författare)
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Embryonic expression of priapulid Wnt genes
- 2019
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Ingår i: Development, Genes and Evolution. - : SPRINGER. - 0949-944X .- 1432-041X. ; 229:4, s. 125-135
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Tidskriftsartikel (refereegranskat)abstract
- Posterior elongation of the developing embryo is a common feature of animal development. One group of genes that is involved in posterior elongation is represented by the Wnt genes, secreted glycoprotein ligands that signal to specific receptors on neighbouring cells and thereby establish cell-to-cell communication. In segmented animals such as annelids and arthropods, Wnt signalling is also likely involved in segment border formation and regionalisation of the segments. Priapulids represent unsegmented worms that are distantly related to arthropods. Despite their interesting phylogenetic position and their importance for the understanding of ecdysozoan evolution, priapulids still represent a highly underinvestigated group of animals. Here, we study the embryonic expression patterns of the complete sets of Wnt genes in the priapulids Priapulus caudatus and Halicryptus spinulosus. We find that both priapulids possess a complete set of 12 Wnt genes. At least in Priapulus, most of these genes are expressed in and around the posterior-located blastopore and thus likely play a role in posterior elongation. Together with previous work on the expression of other genetic factors such as caudal and even-skipped, this suggests that posterior elongation in priapulids is under control of the same (or very similar) conserved gene regulatory network as in arthropods.
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| 17. |
- Janssen, Ralf, 1975-, et al.
(författare)
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A chelicerate Wnt gene expression atlas : novel insights into the complexity of arthropod Wnt-patterning
- 2021
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Ingår i: EvoDevo. - : BioMed Central (BMC). - 2041-9139. ; 12
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Tidskriftsartikel (refereegranskat)abstract
- The Wnt genes represent a large family of secreted glycoprotein ligands that date back to early animal evolution. Multiple duplication events generated a set of 13 Wnt families of which 12 are preserved in protostomes. Embryonic Wnt expression patterns (Wnt-patterning) are complex, representing the plentitude of functions these genes play during development. Here, we comprehensively investigated the embryonic expression patterns of Wnt genes from three species of spiders covering both main groups of true spiders, Haplogynae and Entelegynae, a mygalomorph species (tarantula), as well as a distantly related chelicerate outgroup species, the harvestman Phalangium opilio. All spiders possess the same ten classes of Wnt genes, but retained partially different sets of duplicated Wnt genes after whole genome duplication, some of which representing impressive examples of sub- and neo-functionalization. The harvestman, however, possesses a more complete set of 11 Wnt genes but with no duplicates. Our comprehensive data-analysis suggests a high degree of complexity and evolutionary flexibility of Wnt-patterning likely providing a firm network of mutational protection. We discuss the new data on Wnt gene expression in terms of their potential function in segmentation, posterior elongation, and appendage development and critically review previous research on these topics. We conclude that earlier research may have suffered from the absence of comprehensive gene expression data leading to partial misconceptions about the roles of Wnt genes in development and evolution.
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| 18. |
- Janssen, Ralf, 1975-, et al.
(författare)
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A comprehensive study of arthropod and onychophoran Fox gene expression patterns
- 2022
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Ingår i: PLOS ONE. - : Public Library of Science (PLoS). - 1932-6203. ; 17:7
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Tidskriftsartikel (refereegranskat)abstract
- Fox genes represent an evolutionary old class of transcription factor encoding genes that evolved in the last common ancestor of fungi and animals. They represent key-components of multiple gene regulatory networks (GRNs) that are essential for embryonic development. Most of our knowledge about the function of Fox genes comes from vertebrate research, and for arthropods the only comprehensive gene expression analysis is that of the fly Drosophila melanogaster. For other arthropods, only selected Fox genes have been investigated. In this study, we provide the first comprehensive gene expression analysis of arthropod Fox genes including representative species of all main groups of arthropods, Pancrustacea, Myriapoda and Chelicerata. We also provide the first comprehensive analysis of Fox gene expression in an onychophoran species. Our data show that many of the Fox genes likely retained their function during panarthropod evolution highlighting their importance in development. Comparison with published data from other groups of animals shows that this high degree of evolutionary conservation often dates back beyond the last common ancestor of Panarthropoda.
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| 19. |
- Janssen, Ralf
(författare)
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A curious abnormally developed embryo of the pill millipede Glomeris marginata (Villers, 1789)
- 2013
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Ingår i: ZooKeys. - : Pensoft Publishers. - 1313-2989 .- 1313-2970. ; :276, s. 67-75
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Tidskriftsartikel (refereegranskat)abstract
- This paper reports on an abnormally developed embryo (ADE) of the common pill millipede Glomeris marginata. This ADE represents a modified case of Duplicitas posterior, in which two posterior ends are present, but only one anterior end. While the major posterior germ band of the embryo appears almost normally developed, the minor posterior germ band is heavily malformed, has no clear correlation to the single head, little or no ventral tissue, and a minute amount of yolk. The anterior end of the minor germ band is fused to the ventral side of the major germ band between the first and second trunk segment. At least one appendage of the second trunk segment appears to be shared by the two germ bands. Morphology and position of the minor germ band suggest that the ADE may be the result of an incorrectly established single cumulus [the later posterior segment addition zone (SAZ)]. This differs from earlier reports on D. posterior type ADEs in G. marginata that are likely the result of the early formation of two separate cumuli.
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| 20. |
- Janssen, Ralf, 1975-
(författare)
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A molecular view of onychophoran segmentation
- 2017
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Ingår i: Arthropod structure & development. - : Elsevier. - 1467-8039 .- 1873-5495. ; 46:3, s. 341-353
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Tidskriftsartikel (refereegranskat)abstract
- This paper summarizes our current knowledge on the expression and assumed function of Drosophila and (other) arthropod segmentation gene orthologs in Onychophora, a closely related outgroup to Arthropoda. This includes orthologs of the so-called Drosophila segmentation gene cascade including the Hox genes, as well as other genetic factors and pathways involved in non-drosophilid arthropods. Open questions about and around the topic are addressed, such as the definition of segments in onychophorans, the unclear regulation of conserved expression patterns downstream of non-conserved factors, and the potential role of mesodermal patterning in onychophoran segmentation. (C) 2016 Elsevier Ltd. All rights reserved.
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| 21. |
- Janssen, Ralf, et al.
(författare)
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A review of the correlation of tergites, sternites, and leg pairs in diplopods
- 2006
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Ingår i: Frontiers in Zoology. - : Springer Science and Business Media LLC. - 1742-9994. ; 3:2
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Tidskriftsartikel (refereegranskat)abstract
- In some arthropods there is a discrepancy in the number of dorsal tergites compared to the number of ventral sternites and leg pairs. The posterior tergites of the Diplopoda (millipedes) each cover two sternites and two pairs of legs. This segment arrangement is called diplosegmentation. The molecular nature of diplosegmentation is still unknown. There are even conflicting theories on the way the tergites and sternites/leg pairs should be correlated to each other. The different theories are based either on embryological analyses or on studies of the adult morphology and turned out to be not compatible with each other. We have previously used the expression patterns of segmentation genes in the pill millipede Glomeris marginata (Myriapoda: Diplopoda) to study millipede segmentation. Here we review the existing models on the alignment of tergites and leg pairs in millipedes with special emphasis on the implications the gene expression data have on the debate of tergite and leg pair assignment in millipedes. The remarkable outcome of the gene expression analysis was that (1) there is no coupling of dorsal and ventral segmentation and, importantly, that (2) the boundaries delimiting the tergites do neither correlate to the embryonic boundaries of the dorsal embryonic segments nor to the boundaries of the ventral embryonic segments. Using these new insights, we critically reinvestigated the correlation of tergites, sternites, and leg pairs in millipedes. Our model, which takes into account that the tergite boundaries are different from the dorsal embryonic segment boundaries, provides a solution of the problem of tergite to sternite/leg pair correlation in basal milipedes with non-fused exoskeletal elements and also has implications for derived species with exoskeletal rings. Moreover, lack of coupling of dorsal and ventral segmentation may also explain the discrepancy in numbers of dorsal tergites and ventral leg pairs seen in some other arthropods.
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| 22. |
- Janssen, Ralf
(författare)
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An abnormally developed embryo of the pill millipede Glomeris marginata that lacks dorsal segmental derivatives
- 2011
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Ingår i: Development, Genes and Evolution. - : Springer Science and Business Media LLC. - 0949-944X .- 1432-041X. ; 221:5-6, s. 351-355
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Tidskriftsartikel (refereegranskat)abstract
- The body of arthropods is subdivided in serially homologous units, the so-called segments. In many arthropods, ventral and dorsal segmental tissue typically is aligned in parallel, but is dependent on different genetic inputs. In the pill millipede Glomeris marginata (Myriapoda: Diplopoda), ventral and dorsal segmental patterning is clearly decoupled providing an excellent model for the investigation of ventral versus dorsal segmentation mechanisms. This paper reports on the finding of a single embryo that lacks dorsal segmental and extraembryonic tissue. Ventral derivatives, however, are widely developed normally. This suggests that ventral and dorsal tissue is not only patterned differently, as shown previously, but also that ventral tissue can develop (or at least persist) independently from dorsal tissue. It also suggests a correlation of dorsal segmentation and function of the extraembryonic tissue. This assumed correlation may involve the guidance of the two dorsal hemispheres of the developing embryo dorsally, or that formation and/or maintenance of extraembryonic tissue depends on the input of dorsal segmental tissue. Whether the observed abnormalities are caused by mutation or are the result of otherwise disturbed early development is unclear.
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| 23. |
- Janssen, Ralf, et al.
(författare)
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Aspects of dorso-ventral and proximo-distal limb patterning in onychophorans
- 2015
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Ingår i: Evolution & Development. - : Wiley. - 1520-541X .- 1525-142X. ; 17:1, s. 21-33
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Tidskriftsartikel (refereegranskat)abstract
- Onychophorans (velvet worms) are closely related to the arthropods, but their limb morphology represents a stage before arthropodization (i.e., the segmentation of the limbs). We investigated the expression of onychophoran homologs of genes that are involved in dorso-ventral (DV) and proximo-distal (PD) limb patterning in arthropods. We find that the two onychophoran optomotor-blind (omb) genes, omb-1 and omb-2, are both expressed in conserved patterns in the dorsal ectoderm of the limbs, including the onychophoran antennae (the frontal appendages). Surprisingly, the expression of decapentaplegic (dpp), which acts upstream of omb in Drosophila, is partially reversed in onychophoran limbs compared to its expression in arthropods. A conserved feature of dpp expression in arthropods and onychophorans, however, is the prominent expression of dpp in the tips of developing limbs, which, therefore, may represent the ancestral pattern. The expression patterns of wingless (wg) and H15 are very diverged in onychophorans. The wg gene is only expressed in the limb tips and the single H15 gene is expressed in a few dorsal limb cells, but not on the ventral side. The expression of wg and dpp at the limb tips is one of the three possible alternatives predicted by the topology model of arthropod limb patterning and is, thus, compatible with a conserved function of wg and dpp in the patterning of the PD axis. On the other hand, DV limb gene expression is less conserved, and the specification of ventral fate appears to involve neither wg nor H15 expression.
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| 24. |
- Janssen, Ralf
(författare)
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Comparative analysis of gene expression patterns in the arthropod labrum and the onychophoran frontal appendages, and its implications for the arthropod head problem
- 2017
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Ingår i: EvoDevo. - : Springer Science and Business Media LLC. - 2041-9139. ; 8
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Tidskriftsartikel (refereegranskat)abstract
- The arthropod head problem has troubled scientists for more than a century. The segmental composition of the arthropod head, homology of its appendages, and especially the nature of the most anterior region of the head are still, at least partially, unclear. One morphological feature of the head that is in the center of current debate is the labrum (upper lip), a fleshy appendicular structure that covers the arthropod mouth. One hypothesis is that the labrum represents a fused pair of protocerebral limbs that likely are homologous with the frontal appendages (primary antennae) of extant onychophorans and the so-called great appendages of stem arthropods. Recently, this hypothesis obtained additional support through genetic data, showing that six3, an anterior-specific gene, is exclusively expressed in the arthropod labrum and the onychophoran frontal appendages, providing an additional line of evidence for homology. Here I present data that put this finding into perspective. The outcome of my study shows that the homologization of a morphological structure by the expression of a single genetic factor is potentially misleading.
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| 25. |
- Janssen, Ralf, et al.
(författare)
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Conservation, loss, and redeployment of Wnt ligands in protostomes : implications for understanding the evolution of segment formation
- 2010
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Ingår i: BMC Evolutionary Biology. - : Springer Science and Business Media LLC. - 1471-2148. ; 10, s. 374-
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Tidskriftsartikel (refereegranskat)abstract
- Background: The Wnt genes encode secreted glycoprotein ligands that regulate a wide range of developmental processes, including axis elongation and segmentation. There are thirteen subfamilies of Wnt genes in metazoans and this gene diversity appeared early in animal evolution. The loss of Wnt subfamilies appears to be common in insects, but little is known about the Wnt repertoire in other arthropods, and moreover the expression and function of these genes have only been investigated in a few protostomes outside the relatively Wnt-poor model species Drosophila melanogaster and Caenorhabditis elegans. To investigate the evolution of this important gene family more broadly in protostomes, we surveyed the Wnt gene diversity in the crustacean Daphnia pulex, the chelicerates Ixodes scapularis and Achaearanea tepidariorum, the myriapod Glomeris marginata and the annelid Platynereis dumerilii. We also characterised Wnt gene expression in the latter three species, and further investigated expression of these genes in the beetle Tribolium castaneum. Results: We found that Daphnia and Platynereis both contain twelve Wnt subfamilies demonstrating that the common ancestors of arthropods, ecdysozoans and protostomes possessed all members of all Wnt subfamilies except Wnt3. Furthermore, although there is striking loss of Wnt genes in insects, other arthropods have maintained greater Wnt gene diversity. The expression of many Wnt genes overlap in segmentally reiterated patterns and in the segment addition zone, and while these patterns can be relatively conserved among arthropods and the annelid, there have also been changes in the expression of some Wnt genes in the course of protostome evolution. Nevertheless, our results strongly support the parasegment as the primary segmental unit in arthropods, and suggest further similarities between segmental and parasegmental regulation by Wnt genes in annelids and arthropods respectively. Conclusions: Despite frequent losses of Wnt gene subfamilies in lineages such as insects, nematodes and leeches, most protostomes have probably maintained much of their ancestral repertoire of twelve Wnt genes. The maintenance of a large set of these ligands could be in part due to their combinatorial activity in various tissues.
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