KINGSLEY, Evan P.; RABINOWITZ, Jeremy; LAMBERT, J. David*; University of Rochester; University of Rochester; University of Rochester: A Nanos ortholog is required for endomesoderm specification in the snail Ilyanassa

In the several animal phyla with spiralian development, most of the mesodermal structures are thought to derive from one particular cell, the 4d micromere. This cell is a prominent example of mesendoderm in animal development, and one of the most conserved aspects of spiralian development. The MAPK pathway is required for the differentiation of 4d derivatives in molluscs, and available evidence suggests that it plays the same role in annelids. We have now implicated another developmental regulatory molecule in 4d development: the nanos protein. Nanos is a conserved RNA-binding protein that has roles in germ cell specification and embryonic patterning. In a screen for localized mRNAs in the embryo of the mollusc Ilyanassa obsoleta, we found that a nanos orthologs (IoNanos) was highly enriched in the 3D macromere cell, then restricted to one of its daughter cells, the 4d cell. We have generated loss-of-function phenotypes for IoNanos with morpholino oligonucleotides, and also performed the first comprehensive analysis of the effects of 4d deletion. The IoNanos loss-of-function phenotypes are lacking the same set of 4d derived-structures as 4d deletion larvae, indicating that IoNanos is required for specification of the 4d cell lineage. We discuss the role of Nanos in embryonic patterning and mesendoderm specification.