Full allogeneic fusion of embryos in a holothuroid echinoderm

• Published in: Proceedings of the Royal Society B: Biological Sciences
• Main Authors: Gianasi, Bruno L., Hamel, Jean-François, Mercier, Annie
• Other Authors: Canada Foundation for Innovation, Canadian Centre for Fisheries and Innovation, Department of Fisheries and Aquaculture (DFA) of Newfoundland and Labrador, Research and Development Corporation, Natural Sciences and Engineering Research Council of Canada
• Format: Article in Journal/Newspaper
• Language: English
• Published: The Royal Society 2018
• Subjects: Cucumaria frondosa
• Online Access: http://dx.doi.org/10.1098/rspb.2018.0339; https://royalsocietypublishing.org/doi/pdf/10.1098/rspb.2018.0339; https://royalsocietypublishing.org/doi/full-xml/10.1098/rspb.2018.0339

Whole-body chimaeras (organisms composed of genetically distinct cells) have been directly observed in modular/colonial organisms (e.g. corals, sponges, ascidians); whereas in unitary deuterostosmes (including mammals) they have only been detected indirectly through molecular analysis. Here, we document for the first time the step-by-step development of whole-body chimaeras in the holothuroid Cucumaria frondosa , a unitary deuterostome belonging to the phylum Echinodermata. To the best of our knowledge, this is the most derived unitary metazoan in which direct investigation of zygote fusibility has been undertaken. Fusion occurred among hatched blastulae, never during earlier (unhatched) or later (larval) stages. The fully fused chimaeric propagules were two to five times larger than non-chimaeric embryos. Fusion was positively correlated with propagule density and facilitated by the natural tendency of early embryos to agglomerate. The discovery of natural chimaerism in a unitary deuterostome that possesses large externally fertilized eggs provides a framework to explore key aspects of evolutionary biology, histocompatibility and cell transplantation in biomedical research.