The genomic origin of the unique chaetognath body plan
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ABSTRACT:
PROVIDER: PRJNA1173127 | ENA |
REPOSITORIES: ENA
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Project description:The emergence of animal phyla, each with their unique body plan, was a rapid event in the history of animal life, yet its genomic underpinnings are still poorly understood. Here, we investigate at the genomic, regulatory, and cellular levels the origin of one of the most enigmatic animal phyla, the chaetognaths, whose distinctive organismal characteristics have historically complicated its phylogenetic placement. We show that some of these characteristics are reflected at the cell-type level by the expression of genes originating in the chaetognath lineage, contributing to adaptation to planktonic life at the sensory and structural levels. Chaetognaths belong to the gnathiferan lineage (also including rotifers and several other microscopic phyla), which is marked by accelerated genomic evolution with gene loss and chromosomal rearrangements. Chaetognaths further secondarily acquired thousands of newly duplicated genes, without evidence for a whole genome duplication, yielding, for instance, tandemly expanded Hox genes, as well as many phylum-specific genes. We also detected repeat-rich highly-methylated neocentromeres and a simplified DNA methylation toolkit, which is involved in mobile element repression rather than transcriptional control, a role inherited by trans-splicing. Consistent with fossil evidence, our observations suggest that chaetognaths emerged after a phase of morphological simplification through a reinvention of organ systems paralleled by massive genomic reorganisation, explaining the uniqueness of the chaetognath body plan.
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Project description:Gastrulation marks a landmark event in early embryogenesis, laying the foundation for the three germ layers and body plan formation. While transcriptional and epigenetic regulation during gastrulation has been extensively studied, post-transcriptional mechanisms remain underexplored, partly due to technical constraints and limited access to mammalian embryos. Here, we combine the scalability of gastruloids, an in vivo model of early embryonic development, with a single-cell CRISPR screening platform to systematically dissect post-transcriptional regulators of germ layer differentiation. Our screen uncovers previously unrecognized regulators of mesodermal and endodermal fate and enables cell-type-specific functional characterization with single-cell transcriptomic readout. Focusing on the de-adenylase Cnot8, we demonstrate that Cnot8-mediated poly(A) tail regulation is essential for mesodermal differentiation and proper body axis formation, underscoring the critical role of post-transcriptional control in early mammalian development. Together, our findings support a critical role of poly(A) tail regulation in the patterning of the mammalian embryo and establish gastruloid based single cell CRISPR screens as tool to uncover novel regulators and mechanisms of embryogenesis.
2026-07-13 | GSE302657 | GEO
Project description:While the vertebrate body plan is highly conserved amongst all species of this taxon, extreme variations thereof can be documented in snakes, which display both an absence of limbs and an unusually elongated trunk. As Hox genes are strong candidates both for the making and the evolution of this body plan, their comparative study in such a morphologically diverged group is informative regarding their potential causative importance in these processes. In this work we use an interspecies comparative approach where different aspects of regulation at the HoxD locus are investigated. We find that although spatial collinearity and associated epigenetic mark dynamics are conserved in the corn snake, other regulatory modalities have been largely restructured. A BAC transgenic approach indeed revealed that, while the majority of mesodermal enhancers in vertebrates appear to be mostly located outside of the cluster, the corn snake contains most mesodermal trunk enhancers within the HoxD cluster. We also find that, despite the absence of limbs and an altered Hoxd gene regulation in external genitalia, the bimodal chromatin structure at the corn snake HoxD locus is maintained. The analysis of particular enhancer sequences initially defined in the mouse and further isolated at the snake orthologous locus showed differences in their specificities for the limb and genital bud expression. Of particular interest, a snake counterpart of a mouse limb-only enhancer sequence evolved into a genital-only enhancer. Such a regulatory exaptation suggests that enhancer versatility may have been an important factor to accompany the transition towards the snake body plan. These results show that vertebrate morphological evolution is likely to have been associated with extensive reorganization at the HoxD regulatory landscapes while respecting a very conserved general regulatory framework.
2016-11-05 | GSE79045 | GEO
Project description:While the vertebrate body plan is highly conserved amongst all species of this taxon, extreme variations thereof can be documented in snakes, which display both an absence of limbs and an unusually elongated trunk. As Hox genes are strong candidates both for the making and the evolution of this body plan, their comparative study in such a morphologically diverged group is informative regarding their potential causative importance in these processes. In this work we use an interspecies comparative approach where different aspects of regulation at the HoxD locus are investigated. We find that although spatial collinearity and associated epigenetic mark dynamics are conserved in the corn snake, other regulatory modalities have been largely restructured. A BAC transgenic approach indeed revealed that, while the majority of mesodermal enhancers in vertebrates appear to be mostly located outside of the cluster, the corn snake contains most mesodermal trunk enhancers within the HoxD cluster. We also find that, despite the absence of limbs and an altered Hoxd gene regulation in external genitalia, the bimodal chromatin structure at the corn snake HoxD locus is maintained. The analysis of particular enhancer sequences initially defined in the mouse and further isolated at the snake orthologous locus showed differences in their specificities for the limb and genital bud expression. Of particular interest, a snake counterpart of a mouse limb-only enhancer sequence evolved into a genital-only enhancer. Such a regulatory exaptation suggests that enhancer versatility may have been an important factor to accompany the transition towards the snake body plan. These results show that vertebrate morphological evolution is likely to have been associated with extensive reorganization at the HoxD regulatory landscapes while respecting a very conserved general regulatory framework.
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