Knockout of cyclin dependent kinases 8 and 19 leads to depletion of cyclin C and suppresses spermatogenesis and male fertility in mice
CDK8 and CDK19 are regulatory kinases associated with the transcriptional Mediator complex. We have generated mice with the systemic deletion of both Cdk19 (constitutive knockout) and Cdk8 (inducible knockout). Cdk8/19 double knockout (DKO), in contrast to the deletion of Cdk8 or Cdk19 alone or treatment with a CDK8/19 kinase inhibitor, led to depletion of cyclin C (CcnC), the binding partner of CDK8/19 that has been implicated in CDK8/19-independent functions. DKO males were infertile. The DKO males lacked postmeiotic spermatids and spermatocytes after meiosis I pachytene. Testosterone levels were decreased whereas the amounts of the luteinizing hormone were unchanged. Single cell RNA sequencing showed marked differences in the expression of steroidogenic genes (such as Cyp17a1, Star and Fads) in Leydig cells concomitant with alterations in Sertoli cells and spermatocytes likely associated with impaired synthesis of steroids. Star and Fads were also downregulated in cultivated Leydig cells after DKO. In contrast to DKO, the treatment of Leydig cells with a CDK8/19 inhibitor did not induce the same changes in gene expression, prolonged treatment of mice with a CDK8/19 inhibitor did not affect the size of testis, suggesting that the observed phenotype was likely mediated through kinase-independent activities of CDK8/19, such as CcnC stabilization.