Direct and positive regulation of Caenorhabditis elegans bed-3 by PRDM1/BLIMP1 ortholog BLMP-1.

Caenorhabditis elegans BLMP-1 is the homolog of mammalian PRDM1/BLIMP1 transcriptional repressor and a component of the heterochronic pathway regulating developmental timing. We found that BLMP-1 positively and directly regulates the bed-3 gene required for vulval cell division and molting. blmp-1 mutation or RNAi reduces bed-3 reporter expression and causes phenotype similar to bed-3 mutations. We mapped an enhancer element responsible for bed-3 expression in the vulva and the hypodermis to a 200 bp region in the third intron. Using EMSA, we identified BLMP-1 binding sites within this region. Mutating these sites abolished both in vitro BLMP-1 binding and in vivo enhancer activity. Thus, BLMP-1 directly and positively regulates bed-3 transcription, connecting the heterochronic pathway to regulation of vulval cell division and molting. Recently, C. elegans blmp-1 was found to act as a transcriptional repressor. Thus, C. elegans BLMP-1 acts as a transcriptional activator or a repressor depending on the context.