Stk33 is required for spermatid differentiation and male fertility in mice.

Spermiogenesis is the final phase during sperm cell development in which round spermatids undergo dramatic morphological changes to generate spermatozoa. Here we report that the serine/threonine kinase Stk33 is essential for the differentiation of round spermatids into functional sperm cells and male fertility. Constitutive Stk33 deletion in mice results in severely malformed and immotile spermatozoa that are particularly characterized by disordered structural tail elements.