Identification and developmental expression of Dec2 in zebrafish.

The involvement of Dec2, a member of the basic helix-loop-helix (bHLH) family, in cellular differentiation, hypoxia response, and circadian regulation has been investigated. Here we report the previously unknown spatiotemporal expression of Dec2 in zebrafish embryogenesis. Dec2 is dynamically expressed in zebrafish pineal gland, tract of the postoptic commissure, brain, notochord, heart, common cardinal vein (CCV), axial vein, pronephric duct, swim bladder, and early somites during embryogenesis, which implies that Dec2 is involved in zebrafish central nervous system development, cardiogenesis, and internal organs and somites formation. The embryonic expression patterns of zebrafish Dec2 and its homolog Dec1 partially overlap, but are distinct from each other. The Dec2 expression level was lower than that of Dec1 during zebrafish embryogenesis. Although Dec1 also contributed to zebrafish somites formation, cardiogenesis, and internal organs and central nervous system development, the two Dec genes were not likely to be simply redundant during zebrafish embryogenesis. Our results imply that Dec2, like its homolog Dec1, is involved in zebrafish cardiogenesis, central nervous system development, and internal organs and somites formation with distinct developmental roles.