C. elegans LET-381/FoxF and DMD-4/DMRT control development of the mesodermal HMC endothelial cell

Endothelial cells form the inner layer of blood vessels and play key roles in circulatory system development and function. A variety of endothelial cell types have been described through gene expression and transcriptome studies; nonetheless, the transcriptional programs that specify endothelial cell fate and maintenance are not well understood. To uncover such regulatory programs, we studied the C. elegans Head Mesodermal Cell (HMC), a non-contractile mesodermal cell bearing molecular and functional similarities to vertebrate endothelial cells. Here, we demonstrate that a Forkhead transcription factor, LET-381/FoxF, is required for HMC fate specification and maintenance of HMC gene expression. DMD-4, a Dmrt transcription factor, acts downstream of and in conjunction with LET-381 to mediate HMC fate specification and gene expression maintenance. DMD-4, independently of LET-381, also represses the expression of genes associated with a different, non-HMC, mesodermal fate. Our studies uncover essential roles for FoxF transcriptional regulators in endothelial cell development, and suggest that the identity of FoxF co-functioning target transcription factors promotes specific non-contractile mesodermal fates.