E2f4 and E2f5 are essential for the development of the male reproductive system

The E2F transcription factors are primarily implicated in the regulation of entry and exit from the cell cycle. However, <i>in vivo</i> studies have established additional roles for E2Fs during organ development and homeostasis. With the goal of addressing the intestinal requirements of <i>E2f4</i> and <i>E2f5</i>, we crossed mice carrying <i>Vil-cre, E2f4</i> conditional and <i>E2f5</i> germline alleles. <i>E2f4</i> deletion had no detectable effect on intestinal development. However, <i>E2f4f/f;E2f5+/−;Vil-cre</i> males, but not <i>E2f4f/f;Vil-cre</i> littermates, were unexpectedly sterile. This defect was not due to defective spermatogenesis. Instead, the seminiferous tubules and rete testes showed significant dilation, and spermatozoa accumulated aberrantly in the rete testis and efferent ducts. Our data show that these problems result from defective efferent ducts, a tissue whose primary function is to concentrate sperm through fluid absorption. First, <i>Vil-cre</i> expression, and consequent E2F4 loss, was specific to the efferent ducts and not other reproductive tract tissues. Second, the <i>E2f4f/f;E2f5+/−;Vil-cre</i> efferent ducts had completely lost multiciliated cells and greatly reduced levels of critical absorptive cell proteins: aquaporin1, a water channel protein, and clusterin, an endocytic marker. Collectively, the observed testis phenotypes suggest a fluid flux defect. Remarkably, we observed rete testis dilation prior to the normal time of seminiferous fluid production, arguing that the efferent duct defects promote excessive secretory activity within the reproductive tract. Finally, we also detect key aspects of these testis defects in <i>E2f5</i>−/− mice. Thus, we conclude that <i>E2f4</i> and <i>E2f5</i> display overlapping roles in controlling the normal development of the male reproductive system.