Soubigou, A. | Search bioRxiv

bioRxiv2023

An amphioxus neurula stage cell atlas supports a complex scenario for the emergence of vertebrate head mesoderm

The emergence of new structures can often be linked to the evolution of novel cell types that follows the rewiring of developmental gene regulatory subnetworks. Vertebrates are characterized by a complex body plan compared to the other chordate clades and the question remains of whether and how the emergence of vertebrate morphological innovations can be related to the appearance of new embryonic cell populations. We already proposed, by studying mesoderm development in the cephalochordate amphioxus, a scenario for the evolution of the vertebrate head mesoderm. To further test this scenario at the cell population level, we used scRNA-seq to construct a cell atlas of the amphioxus neurula, stage at which the main mesodermal compartments are specified. Our data allowed us to confirm the presence of a prechordal-plate like territory in amphioxus, and shows that cell populations of the anteriormost somites and of the ventral part of the somites present a transcriptomic profile supporting the homology with vertebrate cranial/pharyngeal and lateral plate mesoderm. Finally, our work provides evidence that the appearance of the specific mesodermal structures of the vertebrate head was associated to both segregation of pre-existing cell populations, and co-option of new genes for the control of myogenesis.

evolutionary biology↗

bioRxiv2020

Regeneration in sponge Sycon ciliatum mimics postlarval development

Somatic cells dissociated from an adult sponge can re-organize and develop into a functional juvenile. However, the extent to which regeneration recapitulates embryonic developmental signaling pathways has remained enigmatic for more than a century. To this end, we have standardized and established a sponge Sycon ciliatum regeneration protocol to achieve consistent regeneration in cell culture. From the morphological analysis, we demonstrated that dissociated sponge cells follow a series of morphological events resembling embryonic and postlarval development. Hence, we propose that sponge regeneration represents somatic development. To support our hypothesis, we performed high-throughput sequencing on regenerating samples and compared the data with regular embryonic and postlarval development of Sycon ciliatum. Our comparative transcriptomic analysis illuminates that sponge regeneration is equally as dynamic as embryogenesis. We find that sponge regeneration is orchestrated by complex regulatory mechanisms by recruiting signaling pathways like those utilized in embryonic development to organize into a functional juvenile. In the current study, we lay down the basic framework to study Sycon ciliatum regeneration. Since sponges are likely to be the first branch of extant multicellular animal and the sister lineage to nearly all animals, we suggest that this system can be explored to study the genetic features underlying the evolution of multicellularity and regeneration.

developmental biology↗