The temporally regulated transcription factor sel-7 controls developmental timing in C. elegans.

The temporal sequence of cell division and differentiation is explicitly controlled for succession and synchrony of developmental events. In this study we describe how the Caenorhabditis elegans gene sel-7 specifies the L3 stage-specific fate of seam cells, which adopt temporal specificities at each of four larval stages. Loss of function of sel-7 causes reiteration of the L2 stage fate at the L3 stage. sel-7 is involved in regulating the temporal expression pattern of hbl-1, which is a key factor in specifying the L2/L3 progression. We also show that sel-7 functions redundantly with other retarded heterochronic genes, including lin-46, daf-12 and the let-7 family miRNAs, in preventing adoption of the L2 fate at later stages. Expression of sel-7 in seam cells is temporally regulated through an evolutionarily conserved regulatory element located in intron 4 of sel-7. We further demonstrate that reiteration of the L2 proliferative seam cell division at the L3 stage in sel-7 mutants requires activity of the transcriptional mediator complex. Our study reveals that sel-7 functions as a novel heterochronic gene in controlling temporal cell identities and also demonstrates a role of the transcriptional mediator complex in integrating temporal information to specify seam cell division patterns in C. elegans.