| 1. |
- Azeez, Abdul, et al.
(författare)
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A Tree Ortholog of APETALA1 Mediates Photoperiodic Control of Seasonal Growth
- 2014
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Ingår i: Current Biology. - : Elsevier BV. - 0960-9822 .- 1879-0445. ; 24, s. 717-724
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Tidskriftsartikel (refereegranskat)abstract
- Background: Photoperiodic control of development plays a key role in adaptation of plants to seasonal changes. A signaling module consisting of CONSTANS (CO) and FLOWERING LOCUS T (FT) mediates in photoperiodic control of a variety of developmental transitions (e. g., flowering, tuberization, and seasonal growth cessation in trees). How this conserved CO/FT module can mediate in the photoperiodic control of diverse unrelated developmental programs is poorly understood.Results: We show that Like-AP1 (LAP1), a tree ortholog of Arabidopsis floral meristem identity gene APETALA1 (AP1), mediates in photoperiodic control of seasonal growth cessation downstream of the CO/FT module in hybrid aspen. Using LAP1 overexpressors and RNAi-suppressed transgenic trees, we demonstrate that short day (SD)-mediated downregulation of LAP1 expression is required for growth cessation. In contrast with AP1 targets in flowering, LAP1 acts on AINTEGUMENTA-like 1 transcription factor, which is implicated in SD-mediated growth cessation. Intriguingly, unlike AP1 in Arabidopsis, ectopic expression of LAP1 fails to induce early flowering in hybrid aspen trees.Conclusions: These results indicate that AP1 ortholog in trees has acquired a novel function in photoperiodic regulation of seasonal growth. Thus, photoperiodic signaling pathway may have diverged downstream of AP1/LAP1 rather than the CO/FT module during evolution. Moreover, control of flowering by the CO/FT module can be uncoupled from its role in photoperiodic control of seasonal growth in trees. Thus, our findings can explain mechanistically how a conserved signaling module can mediate in the control of a highly diverse set of developmental transitions by a similar input signal, namely photoperiod.
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| 2. |
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| 3. |
- Bach, Dominik R., et al.
(författare)
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Human Hippocampus Arbitrates Approach-Avoidance Conflict
- 2014
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Ingår i: Current Biology. - : Elsevier BV. - 0960-9822 .- 1879-0445. ; 24:5, s. 541-547
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Tidskriftsartikel (refereegranskat)abstract
- Animal models of human anxiety often invoke a conflict between approach and avoidance [1, 2]. In these, a key behavioral assay comprises passive avoidance of potential threat and inhibition, both thought to be controlled by ventral hippocampus [2-6]. Efforts to translate these approaches to clinical contexts [7, 8] are hampered by the fact that it is not known whether humans manifest analogous approach-avoidance dispositions and, if so, whether they share a homologous neurobiological substrate [9]. Here, we developed a paradigm to investigate the role of human hippocampus in arbitrating an approach-avoidance conflict under varying levels of potential threat. Across four experiments, subjects showed analogous behavior by adapting both passive avoidance behavior and behavioral inhibition to threat level. Using functional magnetic resonance imaging (fMRI), we observe that threat level engages the anterior hippocampus, the human homolog of rodent ventral hippocampus [10]. Testing patients with selective hippocampal lesions, we demonstrate a causal role for the hippocampus with patients showing reduced passive avoidance behavior and inhibition across all threat levels. Our data provide the first human assay for approach-avoidance conflict akin to that of animal anxiety models. The findings bridge rodent and human research on passive avoidance and behavioral inhibition and furnish a framework for addressing the neuronal underpinnings of human anxiety disorders, where our data indicate a major role for the hippocampus.
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| 4. |
- Breton, Gwenna, et al.
(författare)
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Lactase Persistence Alleles Reveal Partial East African Ancestry of Southern African Khoe Pastoralists
- 2014
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Ingår i: Current Biology. - : Elsevier BV. - 0960-9822 .- 1879-0445. ; 24:8, s. 852-858
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Tidskriftsartikel (refereegranskat)abstract
- The ability to digest milk into adulthood, lactase persistence (LP), as well as specific genetic variants associated with LP, is heterogeneously distributed in global populations [1-4]. These variants were most likely targets of selection when some populations converted from hunter-gatherer to pastoralist or farming lifestyles [5-7]. Specific LP polymorphisms are associated with particular geographic regions and populations [1-4, 8-10]; however, they have not been extensively studied in southern Africa. We investigate the LP-regulatory region in 267 individuals from 13 southern African populations (including descendants of hunter-gatherers, pastoralists, and agropastoralists), providing the first comprehensive study of the LP-regulatory region in a large group of southern Africans. The "East African" LP single-nucleotide polymorphism (SNP) (14010G>C) was found at high frequency (>20%) in a strict pastoralist Khoe population, the Nama of Namibia, suggesting a connection to East Africa, whereas the "European" LP SNP (13910C>T) was found in populations of mixed ancestry. Using genome-wide data from various African populations, we identify admixture (13%) in the Nama, from an Afro-Asiatic group dating to >1,300 years ago, with the remaining fraction of their genomes being from San hunter-gatherers. We also find evidence of selection around the LCT gene among Khoe-speaking groups, and the substantial frequency of the 14010C variant among the Nama is best explained by adaptation to digesting milk. These genome-local and genome-wide results support a model in which an East African group brought pastoralist practices to southern Africa and admixed with local hunter-gatherers to form the ancestors of Khoe people.
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| 5. |
- Cannon, Johanna, 1982-, et al.
(författare)
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Phylogenomic Resolution of the Hemichordate and Echinoderm Clade
- 2014
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Ingår i: Current Biology. - : Elsevier. - 0960-9822 .- 1879-0445. ; 24, s. 2827-2832
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Tidskriftsartikel (refereegranskat)abstract
- Ambulacraria, comprising Hemichordata and Echinodermata, is closely related to Chordata, making it integral to understanding chordate origins and polarizing chordate molecular and morphological characters. Unfortunately, relationships within Hemichordata and Echinoder- mata have remained unresolved, compromising our ability to extrapolate findings from the most closely related molecular and developmental models outside of Chordata (e.g., the acorn worms Saccoglossus kowalevskii and Ptychodera flava and the sea urchin Strongylocentrotus purpuratus). To resolve long-standing phylogenetic issues within Ambulacraria, we sequenced transcriptomes for 14 hemichordates as well as 8 echinoderms and complemented these with existing data for a total of 33 ambulacrarian operational taxonomic units (OTUs). Examination of leaf stability values revealed rhabdopleurid pterobranchs and the enteropneust Stereobalanus canadensis were unstable in placement; therefore, analyses were also run without these taxa. Analyses of 185 genes resulted in reciprocal monophyly of Enteropneusta and Pterobranchia, placed the deep-sea family Torquaratoridae within Ptychoderidae, and confirmed the position of ophiuroid brittle stars as sister to asteroid sea stars (the Asterozoa hypothesis). These results are consistent with earlier perspectives concerning plesiomorphies of Ambulacraria, including pharyngeal gill slits, a single axocoel, and paired hydrocoels and somatocoels. The resolved ambulacrarian phylogeny will help clarify the early evolution of chordate characteristics and has implications for our understanding of major fossil groups, including graptolites and somasteroideans.
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| 6. |
- Chen, Hwei-yen, 1983-, et al.
(författare)
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Condition dependence of male mortality drives the evolution of sex differences in longevity
- 2014
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Ingår i: Current Biology. - : Elsevier BV. - 0960-9822 .- 1879-0445. ; 24:20, s. 2423-2427
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Tidskriftsartikel (refereegranskat)abstract
- Males and females age at different rates and have different life expectancies across the animal kingdom, but what causes the longevity "gender gaps" remains one of the most fiercely debated puzzles among biologists and demographers [1-7]. Classic theory predicts that the sex experiencing higher rate of extrinsic mortality evolves faster aging and reduced longevity [1]. However, condition dependence of mortality [8, 9] can counter this effect by selecting against senescence in whole-organism performance [5, 10]. Contrary to the prevailing view but in line with an emerging new theory [7-9, 11], we show that the evolution of sex difference in longevity depends on the factors that cause sex-specific mortality and cannot be predicted from the mortality rate alone. Experimental evolution in an obligately sexual roundworm, Caenorhabditis remanei, in which males live longer than females, reveals that sexual dimorphism in longevity erodes rapidly when the extrinsic mortality in males is increased at random. We thus experimentally demonstrate evolution of the sexual monomorphism in longevity in a sexually dimorphic organism. Strikingly, when extrinsic mortalityis increased in a way that favors survival of fast-moving individuals, males evolve increased longevities, thereby widening the gender gap. Thus,sex-specific selection on whole-organism performance in males renders them less prone to the ravages of old age than females, despite higher rates of extrinsic mortality. Our results reconcile previous research with recent theoretical breakthroughs [8, 9] by showing that sexual dimorphism inlongevity evolves rapidly and predictably as a result of the sex-specific interactions between environmental hazard and organism's condition.
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| 7. |
- Diard, Médéric, et al.
(författare)
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Antibiotic treatment selects for cooperative virulence of Salmonella typhimurium.
- 2014
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Ingår i: Current Biology. - : Elsevier BV. - 0960-9822 .- 1879-0445. ; 24:17
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Tidskriftsartikel (refereegranskat)abstract
- Antibiotics are powerful therapeutics but are not equally effective against all cells in bacterial populations. Bacteria that express an antibiotic-tolerant phenotype ("persisters") can evade treatment [1]. Persisters can cause relapses of the infection after the end of the therapy [2]. It is still poorly understood whether persistence affects the evolution of bacterial virulence. During infections, persisters have been found preferentially at particular sites within the host [3, 4]. If bacterial virulence factors are required to reach such sites, treatment with antibiotics could impose selection on the expression of virulence genes, in addition to their well-established effects on bacterial resistance. Here, we report that treatment with antibiotics selects for virulence and fosters transmissibility of Salmonella Typhimurium. In a mouse model for Salmonella diarrhea, treatment with the broad-spectrum antibiotic ciprofloxacin reverses the outcome of competition between wild-type bacteria and avirulent mutants that can spontaneously arise during within-host evolution [5]. While avirulent mutants take over the gut lumen and abolish disease transmission in untreated mice, ciprofloxacin tilts the balance in favor of virulent, wild-type bacteria. This is explained by the need for virulence factors to invade gut tissues and form a persistent reservoir. Avirulent mutants remain in the gut lumen and are eradicated. Upon cessation of antibiotic treatment, tissue-lodged wild-type pathogens reseed the gut lumen and thereby facilitate disease transmissibility to new hosts. Our results suggest a general principle by which antibiotic treatment can promote cooperative virulence during within-host evolution, increase duration of transmissibility, and thereby enhance the spread of an infectious disease.
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| 8. |
- Dublon, Ian A. N., et al.
(författare)
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Flying insect swarms
- 2014
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Ingår i: Current Biology. - 0960-9822 .- 1879-0445. ; 24:18, s. R828-R830
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)
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| 9. |
- Fuchs, B., et al.
(författare)
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Regulation of Polyp-to-Jellyfish Transition in Aurelia aurita
- 2014
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Ingår i: Current Biology. - : Elsevier BV. - 0960-9822. ; 24:3, s. 263-273
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Tidskriftsartikel (refereegranskat)abstract
- Background: The life cycle of scyphozoan cnidarians alternates between sessile asexual polyps and pelagic medusa. Transition from one life form to another is triggered by environmental signals, but the molecular cascades involved in the drastic morphological and physiological changes remain unknown. Results: We show in the moon jelly Aurelia aurita that the molecular machinery controlling transition of the sessile polyp into a free-swimming jellyfish consists of two parts. One is conserved and relies on retinoic acid signaling. The second, novel part is based on secreted proteins that are strongly upregulated prior to metamorphosis in response to the seasonal temperature changes. One of these proteins functions as a temperature-sensitive "timer" and encodes the precursor of the strobilation hormone of Aurelia. Conclusions: Our findings uncover the molecule framework controlling the polyp-to-jellyfish transition in a basal metazoan and provide insights into the evolution of complex life cycles in the animal kingdom.
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| 10. |
- He, Ding, et al.
(författare)
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An Alternative Root for the Eukaryote Tree of Life
- 2014
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Ingår i: Current Biology. - : Elsevier BV. - 0960-9822 .- 1879-0445. ; 24:4, s. 465-470
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Tidskriftsartikel (refereegranskat)abstract
- The root of the eukaryote tree of life defines some of the most fundamental relationships among species. It is also critical for defining the last eukaryote common ancestor (LECA), the shared heritage of all extant species. The unikont-bikont root has been the reigning paradigm for eukaryotes for more than 10 years but is becoming increasingly controversial. We developed a carefully vetted data set, consisting of 37 nuclear-encoded proteins of close bacterial ancestry (euBacs) and their closest bacterial relatives, augmented by deep sequencing of the Acrasis kona (Heterolobosea, Discoba) transcriptome. Phylogenetic analysis of these data produces a highly robust, fully resolved global phy- logeny of eukaryotes. The tree sorts all examined eukaryotes into three megagroups and identifies the Discoba, and potentially its parent taxon Excavata, as the sister group to the bulk of known eukaryote diversity, the proposed Neozoa (Amorphea + Stramenopila+Alveolata+Rhizaria+ Plantae [SARP]). All major alternative hypotheses are rejected with as little as w50% of the data, and this resolu- tion is unaffected by the presence of fast-evolving alignment positions or distant outgroup sequences. This ‘‘neozoan- excavate’’ root revises hypotheses of early eukaryote evolution and highlights the importance of the poorly stud- ied Discoba for understanding the evolution of eukaryotic diversity and basic cellular processes.
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