Roles of cyclins in the progression of spermatogenesis

Spermatogenesis is a complex and precise process of differentiation of germ cells, which involves three stages: mitosis of spermatogonia, meiosis of spermatocytes and formation of spermatozoa. The process is controlled by many factors, including regulation of cyclins in spermatogenic cells, which plays a pivotal role. Cyclins form heterologous dimer compounds with protein kinase activity by binding to cyclin-dependent kinases, then phosphorylate multiple proteins and promote the orderly conduct of each phase of the cell cycle. In recent years, cyclins A, B, D and E have been found to play important roles in the regulation of spermatogenesis. This article presents an overview on the roles of these four cyclins in regulating the progression of spermatogenesis.