Abstract: bHLH transcription factors play essential roles in the regulation of eukaryotic growth and development. Animal bHLH transcription factors comprise of 45 families. They are involved in regulating biological processes such as neurogenesis, myogenesis, gut development and response to environmental toxins. In the past two decades, extensive studies had been conducted on identification of bHLH family members and their biological functions in animals. Based on introduction of origin of the 45 animal bHLH family names, this article reviewed the progresses of studies on bHLH family members and functions of three model animals namely mouse, fruit fly and nematode. There are 114, 59 and 42 bHLH proteins in mouse, fruit fly and nematode, respectively. Among them, the functions of 108 mouse, 47 fruit fly and 20 nematode bHLH proteins have been well characterized. Among the 22 nematode bHLH proteins of unknown functions, 15 have not yet been assigned into certain families. This article also explained misused names of several bHLH family members, thus providing clear and overall background information for relevant researchers to conduct in-depth studies on structures and functions of bHLH transcription factors.

Key words: bHLH, Transcription factor, Family member, Regulatory function, Growth and development