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.