Pescoids and chimeras to probe early evo-devo in the fishAstyanax mexicanus

The fish speciesAstyanax mexicanuswith its sighted and blind eco-morphotypes has become an original model to challenge vertebrate developmental evolution. Recently, we demonstrated that phenotypic evolution can be impacted by early developmental events starting from the production of oocytes in the fish ovaries.A. mexicanusoffers an amenable model to test the influence of maternal effect on cell fate decisions during early development, yet the mechanisms by which the information contained in the eggs is translated into specific developmental programs remain obscure due to the lack of specific tools in this emergent model. Here we describe methods for the generation of gastruloids from yolkless-blastoderm explants to test the influence of embryonic and extraembryonic properties on cell fate decisions, as well as the production of chimeric embryos obtained by intermorph cell transplantations to probe cell autonomous or non-autonomous processes. We show thatAstyanaxgastruloids have the potential to recapitulate the main ontogenetic events observed in intact embryos, including the internalization of mesodermal progenitors and eye development, as followed withZic:GFPreporter lines. In addition, intermorph cell grafts resulted in proper integration of exogenous cells into the embryonic tissues, with lineages becoming more restricted from mid-blastula to gastrula. The implementation of these approaches inA. mexicanuswill bring new light on the cascades of events, from the maternal pre-patterning of the early embryo to the evolution of brain regionalization.