E2f5 is a versatile transcriptional activator required for spermatogenesis and multiciliated cell differentiation in zebrafish.

E2f5 is a member of the E2f family of transcription factors that play essential roles during many cellular processes. E2f5 was initially characterized as a transcriptional repressor in cell proliferation studies through its interaction with the Retinoblastoma (Rb) protein for inhibition of target gene transcription. However, the precise roles of E2f5 during embryonic and post-embryonic development remain incompletely investigated. Here, we report that zebrafish E2f5 plays critical roles during spermatogenesis and multiciliated cell (MCC) differentiation. Zebrafish e2f5 mutants develop exclusively as infertile males. In the mutants, spermatogenesis is arrested at the zygotene stage due to homologous recombination (HR) defects, which finally leads to germ cell apoptosis. Inhibition of cell apoptosis in e2f5;tp53 double mutants rescued ovarian development, although oocytes generated from the double mutants were still abnormal, characterized by aberrant distribution of nucleoli. Using transcriptome analysis, we identified dmc1, which encodes an essential meiotic recombination protein, as the major target gene of E2f5 during spermatogenesis. E2f5 can bind to the promoter of dmc1 to promote HR, and overexpression of dmc1 significantly increased the fertilization rate of e2f5 mutant males. Besides gametogenesis defects, e2f5 mutants failed to develop MCCs in the nose and pronephric ducts during early embryonic stages, but these cells recovered later due to redundancy with E2f4. Moreover, we demonstrate that ion transporting principal cells in the pronephric ducts, which remain intercalated with the MCCs, do not contain motile cilia in wild-type embryos, while they generate single motile cilia in the absence of E2f5 activity. In line with this, we further show that E2f5 activates the Notch pathway gene jagged2b (jag2b) to inhibit the acquisition of MCC fate as well as motile cilia differentiation by the neighboring principal cells. Taken together, our data suggest that E2f5 can function as a versatile transcriptional activator and identify novel roles of the protein in spermatogenesis as well as MCC differentiation during zebrafish development. Author summary E2f family of transcription factors play essential roles during many cellular processes by activating or inhibiting target gene expression. E2F5 is recognized as a transcriptional repressor during cell-cycle progression. However, the role of E2f5 during embryonic development has not been fully investigated. Here, we show that E2f5 is required both for spermatogenesis and multiciliated cell differentiation in zebrafish. Specifically, E2f5 regulates homologous recombination, a central event in meiosis, by transactivating the expression of dmc1. Loss of E2f5 leads to spermatogenesis defects due to meiosis arrest. In addition, E2f5 plays an essential role during the differentiation of multiciliated cells and ion transporting principal cells in the pronephric ducts (embryonic zebrafish kidney). We showed that principal cells were devoid of cilia in the proximal straight tubule of pronephric ducts, while ectopic cilia developed in these cells due to lateral inhibition defects in the absence of E2f5 protein. Our data suggest that E2f5 functions as a versatile transcriptional activator during vertebrate development.