Isolation and characterization of the activated B-cell factor 1 homolog in Caenorhabditis elegans

Members of the basic helix–loop–helix (bHLH) family of transcription factors regulate a wide array of developmental processes in many cell types, including cell fate specification, differentiation and morphogenesis. Our studies describe the cloning of a gene from the nematode Caenorhabditis elegans that is closely related to the vertebrate-activated B-cell factor (ABF) gene. The nematode gene product CeABF-1 was detected by northern blot analysis from RNA isolated from pooled nematodes representing different developmental stages. The developmental expression profile of CeABF-1 was shown by RT–PCR analysis to be predominantly expressed in the larval stages L3 and L4, with lower levels observed in the L2 larval stage and adult. We also show that CeABF-1 is capable of forming heterodimers with E2A proteins and binding E-box target sites. Mammalian cells transfected with CeABF-1 expression plasmids were capable of blocking E2A-mediated gene transcription, but full repression activity required the presence of two conserved amino acid residues found within the first helix of the CeABF-1 bHLH domain. These results suggest a conserved mechanism of gene repression between certain class II bHLH and class I bHLH proteins found in vertebrates and invertebrates.