Duplication of spiralian-specific TALE genes and evolution of the blastomere specification mechanism in the bivalve lineage.

These results suggest that, in addition to their ancestral role in quartet specification, certain SPILE genes in mussels contribute to the specification of the C and D quadrants. We suggest that the expansion of SPILE genes in the bivalve lineage contributed to the evolution of a unique cell fate specification pattern in bivalves.