A large transcribed enhancer region regulates C. elegans bed-3 and the development of egg laying muscles

Gene expression is regulated by the interaction of the RNA polymerase with various transcription factors at promoter and enhancer elements. Transcriptome analyses found that many non-protein-coding regions are transcribed to produce long non-coding RNAs and enhancer-associated RNAs. Production of these transcripts is associated with activation of nearby protein-coding genes, and at least in some cases, the transcripts themselves mediate this activation. Non-coding transcripts are also reported from large enhancers or clusters of enhancers. However, not much is known about the function of large transcribed enhancer regions during organismal development. Here we investigated a transcribed 10.6 kb intergenic region located upstream of the C. elegans bed-3 gene. We found that parts of this region exhibit tissue-specific promoter and enhancer activities. Deletion of the region disrupts egg laying, a phenotype also observed in bed-3 mutants, but with the severity correlating with the size of the deletion. This phenotype is not caused by overall reduction in bed-3 expression. Rather, deletions reduce bed-3 expression specifically in the mesoderm lineage. We found that bed-3 has a previously unknown function in the generation of sex myoblast (SM) cells from the M lineage, and deletions cause loss of SM cells leading to loss of vulval muscles required for egg laying. Furthermore, injection of dsRNA targeting non-coding transcripts from this region disrupted egg laying in the wild type but not in RNAi-defective mutants. Therefore, the region upstream of bed-3 is required for robust expression of bed-3 in a specific tissue, and non-coding transcripts may mediate this interaction.