Periodic Reporting for period 3 - EVOCELFATE (Evolution of cell fate specification modes in spiral cleavage)
Période du rapport: 2022-02-01 au 2023-07-31
Spiral cleavage is a conserved mode of development ancestral to one of the largest groups of animals–Spiralia. During spiral cleavage, embryos can specify their cell fates (i.e. the progenitor cell of posterodorsal structures) in two ways, either conditionally –via cell interactions– or autonomously –via segregation of molecules deposited in the oocyte by the mother. This variation occurs naturally, even between closely related species, and has been related to the precocious formation of adult characters in larvae of autonomous spiral-cleaving species. How spiralian lineages repeatedly shifted between these two cell fate specification modes is largely unexplored, because the mechanisms controlling spiral cleavage are still poorly characterized.
This project tests the hypothesis that maternal chromatin and transcriptional regulators differentially incorporated in oocytes with autonomous spiral cleavage explain the evolution of this mode of cell fate specification. Through a comparative approach, we will combine bioinformatics, live imaging, and molecular and experimental techniques to: (i) Comprehensively identify differentially supplied maternal factors among spiral cleaving oocytes with distinct cell fate specification modes using comparative RNA-seq and proteomics; (ii) Uncover the developmental mechanisms driving conditional spiral cleavage, which is the ancestral embryonic mode; and (iii) Investigate how maternal chromatin and transcriptional regulators define early cell fates, and whether these factors account for the repeated evolution of autonomous specification modes.
Our results will fill a large knowledge gap in our understanding of spiral cleavage and its evolution. In a broader context, this project will deliver fundamental insights into two core questions in evo-devo: how early embryonic programs evolve, and how they contribute to phenotypic change.
This project tests the hypothesis that maternal chromatin and transcriptional regulators differentially incorporated in oocytes with autonomous spiral cleavage explain the evolution of this mode of cell fate specification. Through a comparative approach, we will combine bioinformatics, live imaging, and molecular and experimental techniques to: (i) Comprehensively identify differentially supplied maternal factors among spiral cleaving oocytes with distinct cell fate specification modes using comparative RNA-seq and proteomics; (ii) Uncover the developmental mechanisms driving conditional spiral cleavage, which is the ancestral embryonic mode; and (iii) Investigate how maternal chromatin and transcriptional regulators define early cell fates, and whether these factors account for the repeated evolution of autonomous specification modes.
Our results will fill a large knowledge gap in our understanding of spiral cleavage and its evolution. In a broader context, this project will deliver fundamental insights into two core questions in evo-devo: how early embryonic programs evolve, and how they contribute to phenotypic change.
Reached the midst of this project, our team has made progress in all three proposed objectives. We have generated transcriptomic and proteomic data for oocytes of annelid species with distinct modes of spiral cleavage, and we are now investigating how differences in the maternal determinants might account for changes in the timing of specification of the progenitor cells. We have also made good progress in characterising the mechanisms controlling conditional spiral cleavage in the annelid Owenia fusiformis, which we are establishing as a tractable model species for developmental biology. We have characterised the regulatory networks controlling the specification of the embryonic organiser (manuscript under review) and we have characterised the genome-wide transcriptomic and regulatory dynamics underpinning conditional spiral cleavage (manuscript in preparation). This has allowed us to demonstrate that conserved molecular mechanisms control conditional spiral cleavage, and that autonomous specification evolved repeatedly through the loss of an ERK1/2-mediated embryonic organiser in annelids. Lastly, we have established cutting-edge approaches for epigenomic profiling in annelid embryos, which we are currently exploiting to investigate how differences in chromatin accessibility, DNA methylation and histone post-translational modifications impact the evolution and control of cell-fate specification dynamics in annelid species.
Our work so far is generating unprecedented datasets for the study of spiral cleavage in annelid embryos and spiralians in general. Our data in Owenia fusiformis is transforming current views on spiral cleavage, demonstrating that conserved, ancient molecular mechanisms control spiral cleavage, which have subsequently diverged to generate the diversity of developmental modes observed today in Spiralia. Our progress on establishing epigenomic profiling methods in spiralian embryos combined with new high-quality genomic data that my lab is generating is also providing fresh views on how spiral cleavage is controlled, from changes in genome sequence and genome regulation to distinct dynamics of gene expression and cell behaviour. In the future, our team will leverage these tools and datasets to generate a more functional and mechanistic understanding of the exact role of differentially deployed maternal determinants during early spiral cleavage.