The metazoan history of the COE transcription factors. Selection of a variant HLH motif by mandatory inclusion of a duplicated exon in vertebrates

<p>Abstract</p> <p>Background</p> <p>The increasing number of available genomic sequences makes it now possible to study the evolutionary history of specific genes or gene families. Transcription factors (TFs) involved in regulation of gene-specific expression are key players in the evolution of metazoan development. The low complexity COE (Collier/Olfactory-1/Early B-Cell Factor) family of transcription factors constitutes a well-suited paradigm for studying evolution of TF structure and function, including the specific question of protein modularity. Here, we compare the structure of <it>coe </it>genes within the metazoan kingdom and report on the mechanism behind a vertebrate-specific exon duplication.</p> <p>Results</p> <p>COE proteins display a modular organisation, with three highly conserved domains : a COE-specific DNA-binding domain (DBD), an Immunoglobulin/Plexin/transcription (IPT) domain and an atypical Helix-Loop-Helix (HLH) motif. Comparison of the splice structure of <it>coe </it>genes between cnidariae and bilateriae shows that the ancestral COE DBD was built from 7 separate exons, with no evidence for exon shuffling with other metazoan gene families. It also confirms the presence of an ancestral H1LH2 motif present in all COE proteins which partly overlaps the repeated H2d-H2a motif first identified in rodent EBF. Electrophoretic Mobility Shift Assays show that formation of COE dimers is mediated by this ancestral motif. The H2d-H2a α-helical repetition appears to be a vertebrate characteristic that originated from a tandem exon duplication having taken place prior to the splitting between gnathostomes and cyclostomes. We put-forward a two-step model for the inclusion of this exon in the vertebrate transcripts.</p> <p>Conclusion</p> <p>Three main features in the history of the <it>coe </it>gene family can be inferred from these analyses: (i) each conserved domain of the ancestral <it>coe </it>gene was built from multiple exons and the same scattered structure has been maintained throughout metazoan evolution. (ii) There exists a single <it>coe </it>gene copy per metazoan genome except in vertebrates. The H2a-H2d duplication that is specific to vertebrate proteins provides an example of a novel vertebrate characteristic, which may have been fixed early in the gnathostome lineage. (iii) This duplication provides an interesting example of counter-selection of alternative splicing.</p

Evolution of Axis Specification Mechanisms in Jawed Vertebrates: Insights from a Chondrichthyan

The genetic mechanisms that control the establishment of early polarities and their link with embryonic axis specification and patterning seem to substantially diverge across vertebrates. In amphibians and teleosts, the establishment of an early dorso-ventral polarity determines both the site of axis formation and its rostro-caudal orientation. In contrast, amniotes retain a considerable plasticity for their site of axis formation until blastula stages and rely on signals secreted by extraembryonic tissues, which have no clear equivalents in the former, for the establishment of their rostro-caudal pattern. The rationale for these differences remains unknown. Through detailed expression analyses of key development genes in a chondrichthyan, the dogfish Scyliorhinus canicula, we have reconstructed the ancestral pattern of axis specification in jawed vertebrates. We show that the dogfish displays compelling similarities with amniotes at blastula and early gastrula stages, including the presence of clear homologs of the hypoblast and extraembryonic ectoderm. In the ancestral state, these territories are specified at opposite poles of an early axis of bilateral symmetry, homologous to the dorso-ventral axis of amphibians or teleosts, and aligned with the later forming embryonic axis, from head to tail. Comparisons with amniotes suggest that a dorsal expansion of extraembryonic ectoderm, resulting in an apparently radial symmetry at late blastula stages, has taken place in their lineage. The synthesis of these results with those of functional analyses in model organisms supports an evolutionary link between the dorso-ventral polarity of amphibians and teleosts and the embryonic-extraembryonic organisation of amniotes. It leads to a general model of axis specification in gnathostomes, which provides a comparative framework for a reassessment of conservations both among vertebrates and with more distant metazoans

Molecular Characterization of the Gastrula in the Turtle Emys orbicularis: An Evolutionary Perspective on Gastrulation

Due to the presence of a blastopore as in amphibians, the turtle has been suggested to exemplify a transition form from an amphibian- to an avian-type gastrulation pattern. In order to test this hypothesis and gain insight into the emergence of the unique characteristics of amniotes during gastrulation, we have performed the first molecular characterization of the gastrula in a reptile, the turtle Emys orbicularis. The study of Brachyury, Lim1, Otx2 and Otx5 expression patterns points to a highly conserved dynamic of expression with amniote model organisms and makes it possible to identify the site of mesoderm internalization, which is a long-standing issue in reptiles. Analysis of Brachyury expression also highlights the presence of two distinct phases, less easily recognizable in model organisms and respectively characterized by an early ring-shaped and a later bilateral symmetrical territory. Systematic comparisons with tetrapod model organisms lead to new insights into the relationships of the blastopore/blastoporal plate system shared by all reptiles, with the blastopore of amphibians and the primitive streak of birds and mammals. The biphasic Brachyury expression pattern is also consistent with recent models of emergence of bilateral symmetry, which raises the question of its evolutionary significance

Molecular Characterization of the Gastrula in the Turtle Emys orbicularis: An Evolutionary Perspective on Gastrulation

Due to the presence of a blastopore as in amphibians, the turtle has been suggested to exemplify a transition form from an amphibian- to an avian-type gastrulation pattern. In order to test this hypothesis and gain insight into the emergence of the unique characteristics of amniotes during gastrulation, we have performed the first molecular characterization of the gastrula in a reptile, the turtle Emys orbicularis. The study of Brachyury, Lim1, Otx2 and Otx5 expression patterns points to a highly conserved dynamic of expression with amniote model organisms and makes it possible to identify the site of mesoderm internalization, which is a long-standing issue in reptiles. Analysis of Brachyury expression also highlights the presence of two distinct phases, less easily recognizable in model organisms and respectively characterized by an early ring-shaped and a later bilateral symmetrical territory. Systematic comparisons with tetrapod model organisms lead to new insights into the relationships of the blastopore/blastoporal plate system shared by all reptiles, with the blastopore of amphibians and the primitive streak of birds and mammals. The biphasic Brachyury expression pattern is also consistent with recent models of emergence of bilateral symmetry, which raises the question of its evolutionary significance

A922 Sequential measurement of 1 hour creatinine clearance (1-CRCL) in critically ill patients at risk of acute kidney injury (AKI)

Meeting abstrac

Differentiation of EpiLCs on micro-patterned substrates generated by micro-contact printing.

International audienceDuring the last decades, signaling pathways responsible for the initiation of gastrulation in mammalian embryos have been identified. However, the physical rules governing the tissue spatial patterning and the extensive morphogenetic movements occurring during that process are still elusive. Progress on these issues is slowed by the difficulty to record or perturb the patterning events in real time, especially in mammalian embryos that develop in utero. Because they permit easy observation and manipulation, in vitro model systems offer an exciting opportunity to dissect the rules governing the organization of the mammalian gastrula. For instance, it is sufficient to cultivate human Embryonic Stem Cells on micropatterned substrates to reveal their self-organization potential. We present here a method to obtain micropatterned mouse Epiblast Like Cells colonies, providing a convenient way to compare spatial organization of mouse and human pluripotent stem cells and to complement the characterization of mutant embryos in a controlled environment