| 1. |
- Heingård, Miriam, et al.
(author)
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FoxB, a new and highly conserved key factor in arthropod dorsal-ventral (DV) limb patterning
- 2019
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In: EvoDevo. - : BMC. - 2041-9139. ; 10
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Journal article (peer-reviewed)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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| 2. |
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| 3. |
- Hogvall, Mattias, et al.
(author)
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Gene expression analysis of potential morphogen signalling modifying factors in Panarthropoda
- 2018
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In: EvoDevo. - : BMC. - 2041-9139. ; 9
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Journal article (peer-reviewed)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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| 4. |
- Hogvall, Mattias, 1984-
(author)
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Investigation of Hox gene expression and Wnt-signalling in basally branching ecdysozoans
- 2018
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Doctoral thesis (other academic/artistic)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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| 5. |
- Högvall, Mattias, et al.
(author)
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Embryonic expression of priapulid Wnt genes
- 2019
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In: Development, Genes and Evolution. - : SPRINGER. - 0949-944X .- 1432-041X. ; 229:4, s. 125-135
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Journal article (peer-reviewed)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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| 6. |
- Janssen, Ralf, 1975-
(author)
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A molecular view of onychophoran segmentation
- 2017
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In: Arthropod structure & development. - : Elsevier. - 1467-8039 .- 1873-5495. ; 46:3, s. 341-353
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Journal article (peer-reviewed)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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| 7. |
- Janssen, Ralf, et al.
(author)
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Aspects of dorso-ventral and proximo-distal limb patterning in onychophorans
- 2015
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In: Evolution & Development. - : Wiley. - 1520-541X .- 1525-142X. ; 17:1, s. 21-33
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Journal article (peer-reviewed)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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| 8. |
- Janssen, Ralf
(author)
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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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In: EvoDevo. - : Springer Science and Business Media LLC. - 2041-9139. ; 8
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Journal article (peer-reviewed)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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| 9. |
- Janssen, Ralf, 1975-, et al.
(author)
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Embryonic expression of a Long Toll (Loto) gene in the onychophorans Euperipatoides kanangrensis and Cephalofovea clandestina
- 2018
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In: Development, Genes and Evolution. - : Springer Science and Business Media LLC. - 0949-944X .- 1432-041X. ; 228:3-4, s. 171-178
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Journal article (peer-reviewed)abstract
- Recent research has shown that Toll genes, and in particular a newly defined class of Toll genes, the so-called Long Toll Genes (Loto genes), are crucial factors in embryogenesis. In arthropods, they are involved in axis formation via a process called convergent extension (CE). A hallmark of Loto genes is their relatively (compared to other Toll genes) high number of leucine-rich repeat elements (LRRs) coupled with the fact that they are expressed in transverse stripes in all segments, or a subset of segments, patterns that are reminiscent of classical segmentation genes such as the pair-rule genes. Onychophorans represent a close outgroup to the arthropods; however, their embryonic development differs substantially. It is unclear if convergent extension contributes to onychophoran germ band formation and, if so, whether Loto genes are involved in governing this process. This study identifies a single onychophoran Toll gene from a sequenced embryonic transcriptome in two onychophoran species. The identified gene shows sequence and expression pattern characteristics of Loto genes. However, its expression pattern also comprises some general differences to arthropod Loto genes that are involved in CE.
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| 10. |
- Janssen, Ralf, 1975-, et al.
(author)
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Embryonic expression patterns and phylogenetic analysis of panarthropod sox genes : insight into nervous system development, segmentation and gonadogenesis
- 2018
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In: BMC Evolutionary Biology. - : Springer Science and Business Media LLC. - 1471-2148. ; 18
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Journal article (peer-reviewed)abstract
- Background: Sox (Sry-related high-mobility-group box) genes represent important factors in animal development. Relatively little, however, is known about the embryonic expression patterns and thus possible function(s) of Sox genes during ontogenesis in panarthropods (Arthropoda+Tardigrada+Onychophora). To date, studies have been restricted exclusively to higher insects, including the model system Drosophila melanogaster, with no comprehensive data available for any other arthropod group, or any tardigrade or onychophoran.Results: This study provides a phylogenetic analysis of panarthropod Sox genes and presents the first comprehensive analysis of embryonic expression patterns in the flour beetle Tribolium castaneum (Hexapoda), the pill millipede Glomeris marginata (Myriapoda), and the velvet worm, Euperipatoides kanangrensis (Onychophora). 24 Sox genes were identified and investigated: 7 in Euperipatoides, 8 in Glomeris, and 9 in Tribolium. Each species possesses at least one ortholog of each of the five expected Sox gene families, B, C, D, E, and F, many of which are differentially expressed during ontogenesis.Conclusion: Sox gene expression (and potentially function) is highly conserved in arthropods and their closest relatives, the onychophorans. Sox B, C and D class genes appear to be crucial for nervous system development, while the Sox B genes Dichaete (D) and Sox21b likely play an additional conserved role in panarthropod segmentation. The Sox B gene Sox21a likely has a conserved function in foregut and Malpighian tubule development, at least in Hexapoda. The data further suggest that Sox D and E genes are involved in mesoderm differentiation, and that Sox E genes are involved in gonadal development.The new data expand our knowledge about the expression and implied function of Sox genes to Mandibulata (Myriapoda+Pancrustacea) and Panarthropoda (Arthropoda+Onychophora).
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