Promotion of oogenesis and embryogenesis in the C. elegans gonad by EFL-1/DPL-1 (E2F) does not require LIN-35 (pRB)

In Caenorhabditis elegans, EFL-1 (E2F), DPL-1 (DP) and LIN-35 (pRb) act coordinately in somatic tissues to inhibit ectopic cell division, probably by repressing the expression of target genes. EFL-1, DPL-1 and LIN-35 are also present in the germline, but do not always act together. Strong loss-of-function mutations in either efl-1 or dpl-1 cause defects in oogenesis that result in sterility, while lin-35 mutants are fertile with reduced broods. Microarray-based expression profiling of dissected gonads from efl-1, dpl-1 and lin-35 mutants reveals that EFL-1 and DPL-1 promote expression of an extensively overlapping set of target genes, consistent with the expectation that these two proteins function as a heterodimer. Regulatory regions upstream of many of these target genes have a canonical E2F-binding site, suggesting that their regulation by EFL-1/DPL-1 is direct. Many EFL-1/DPL-1 responsive genes encode proteins required for oogenesis and early embryogenesis, rather than cell cycle components. By contrast, LIN-35 appears to function primarily as a repressor of gene expression in the germline, and the genes that it acts on are for the most part distinct from those regulated by EFL-1 and/or DPL-1. Thus, in vivo, C. elegans E2F directly promotes oogenesis and embryogenesis through the activation of a tissue-specific transcriptional program that does not require LIN-35.