A genome-wide survey on basic helix-loop-helix transcription factors in rat and mouse

The basic helix-loop-helix (bHLH) proteins play essential roles in a wide range of developmental processes in higher organisms. bHLH family members have been identified in over 20 organisms, including nematode, fruit fly, and human. Our study identified 114 rat and 14 additional mouse bHLH members in rat and mouse genomes, respectively. Phylogenetic analyses revealed that both rat and mouse had 49, 26, 15, 4, 12, and 4 bHLH members in groups A, B, C, D, E, and F, respectively. Only the rat Mxi1 gene has two copies in the genome. All other rat bHLH genes and all mouse bHLH genes are single-copy genes. The chromosomal distribution pattern of mouse, rat, and human bHLH genes suggests the emergence of some bHLH genes through gene duplication, which probably happened at least before the divergence of vertebrates from invertebrates. The present study provides useful information for future studies using rat as a model animal for mammalian development. X. Zheng and Y. Wang are jointly first authors. An erratum to this article can be found at