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 PLOS GENETICS

Idiopathic scoliosis (IS) is the most common spinal deformity diagnosed in childhood or early adolescence, while the underlying pathogenesis of this serious condition remains largely unknown. Here, we report zebrafish ccdc57 mutants exhibiting scoliosis during late development, similar to that observed in human adolescent idiopathic scoliosis (AIS). Zebrafish ccdc57 mutants developed hydrocephalus due to cerebrospinal fluid (CSF) flow defects caused by uncoordinated cilia beating in ependymal cells. Mechanistically, Ccdc57 localizes to ciliary basal bodies and controls the planar polarity of ependymal cells through regulating the organization of microtubule networks and proper positioning of basal bodies. Interestingly, ependymal cell polarity defects were first observed in ccdc57 mutants at approximately 17 days postfertilization, the same time when scoliosis became apparent and prior to multiciliated ependymal cell maturation. We further showed that mutant spinal cord exhibited altered expression pattern of the Urotensin neuropeptides, in consistent with the curvature of the spine. Strikingly, human IS patients also displayed abnormal Urotensin signaling in paraspinal muscles. Altogether, our data suggest that ependymal polarity defects are one of the earliest sign of scoliosis in zebrafish and disclose the essential and conserved roles of Urotensin signaling during scoliosis progression.

Spinal cord injury (SCI) can cause long‐lasting disability in mammals due to the lack of axonal regrowth together with the inability to reinitiate spinal neurogenesis at the injury site. Deciphering the mechanisms that regulate the proliferation and differentiation of neural progenitor cells is critical for understanding spinal neurogenesis after injury. Compared with mammals, zebrafish show a remarkable capability of spinal cord regeneration. Here, we show that Rassf7a, a member of the Ras‐association domain family, promotes spinal cord regeneration after injury. Zebrafish larvae harboring a rassf7a mutation show spinal cord regeneration and spinal neurogenesis defects. Live imaging shows abnormal asymmetric neurogenic divisions and spindle orientation defects in mutant neural progenitor cells. In line with this, the expression of rassf7a is enriched in neural progenitor cells. Subcellular analysis shows that Rassf7a localizes to the centrosome and is essential for cell cycle progression. Our data indicate a role for Rassf7a in modulating spindle orientation and the proliferation of neural progenitor cells after spinal cord injury.