Genome-wide identification and expression profiling of the Wnt gene family in three bivalve molluscs

Cellular signaling initiated by various secreted, cysteine-rich Wnt proteins plays essential roles in regulating animal development and cell sternness. By virtue of its functional diversity and importance, the Wnt gene family has received substantial research interests in a variety of animal species, from invertebrates to vertebrates. However, for bivalve molluscs, one of the ancient bilaterian groups with high morphological diversity, systematic identification and analysis of the Wnt gene family remain lacking. To shed some light on the evolutionary dynamics of this gene family and obtain a more comprehensive understanding, we analyzed the characteristics of the Wnt gene family in three bivalve molluscs, with both genome and extensive transcriptomic resources. Investigation of genomic signatures, functional domains as well as phylogenetic relationships was conducted, and 12, 11, 12 subfamilies were identified in Yesso scallop, Zhikong scallop and Pacific oyster respectively. Spatiotemporal expression profiling suggested that, some bivalve Wnts might coordinate and participate in adult organ/tissue morphogenesis and homeostasis as well as early embryonic development. The transcriptional regulation of oyster Wnt genes showed dynamic and responsive patterns under different environmental stresses, indicating that Writs may play a role in coping with challenging intertidal environments in bivalves. To our best knowledge, this study presents the first genome-wide study of Wnt gene family in bivalves, and our findings would assist in better understanding of Wnt function and evolution in bivalve molluscs.