Early Activation of MAPK and Apoptosis in Nutritive Embryos of Calyptraeid Gastropods

Abstract

Investigation of alternative phenotypes, different morphologies produced by a single genome, has contributed novel insights into development and evolution. Yet, the mechanisms underlying developmental switch points between alternative phenotypes remain poorly understood. The calyptraeid snails Crepidula navicella and Calyptraea lichen produce two phenotypes: viable and nutritive embryos, where nutritive embryos arrest their development after gastrulation and are ingested by their viable siblings as a form of intracapsular nutrition. Here, we investigate the activity of mitogen-activated protein kinase (MAPK, ERK1/2) and apoptosis during early cleavage. MAPK and apoptosis, found in a previous transcriptomic study, are known to be involved in organization of other spiralian embryos and nutritive embryo development, respectively. In the model Crepidula fornicata, MAPK activation begins at the 16-cell stage. In contrast, we discovered in C. navicella and C. lichen that many embryos begin MAPK activation at the one-cell stage. A subset of embryos shows a similar pattern of MAPK activation to C. fornicata at later stages. In all stages where MAPK is detected, the activation pattern is highly variable, frequently occurring in all quadrants or in multiple tiers of cells. We also detected apoptosis in cleaving embryos, while C. fornicata and Crepidula lessoni, which do not produce nutritive embryos, show no signs of apoptosis during cleavage. Our results show that MAPK and apoptosis are expressed during early development in species with nutritive embryos, and raises the possibility that these processes may play a role and even interact with one another in producing the nutritive embryo phenotype.

Ancestral form and function of larval feeding structures are retained during the development of non-planktotrophic gastropods

“…Calyptraeid systematics has received recent detailed attention (Collin 2000;2001;Collin et al 2007;Véliz et al 2012;Collin 2019) and the phylogeny of the group is wellresolved (Collin 2003a, b). A variety of species are commonly used in developmental biology (e.g., Conklin 1897; Henry et al 2006;Hejnol et al 2007;Henry and Perry 2008;Henry et al 2010;Lesoway et al 2014Lesoway et al , 2016Lesoway et al 2017), and Crepidula atrasolea is on its way to becoming a model system for Evo-Devo research (Henry et al 2017;Lesoway and Henry 2019). (Collin 2004).…”