Stage-specific expression of testis-specific protein kinase 1 (TESK1) in rat spermatogenic cells.

TESK1 (testis-specific protein kinase 1) is a serine/threonine kinase, with a unique structure composed of an N-terminal protein kinase domain and a C-terminal proline-rich domain. Northern blot analysis revealed that TESK1 mRNA is predominantly expressed in testicular germ cells. We present here evidence that expression of TESK1 mRNA and protein in the rat testes is developmentally regulated and increases after 20-22 postnatal days. To identify cells which express TESK1 mRNA and protein during male germ cell differentiation, in situ hybridization and immunohistochemistry were done using frozen sections of adult rat testes. Prominent expression of TESK1 mRNA and protein was detected in testicular germ cells at stages of late pachytene spermatocytes to round spermatids, but not in somatic cells such as Sertoli and Leydig cells. Expression of TESK1 mRNA and protein at specific stages of testicular germ cells suggests a role for this kinase in spermatogenesis, particularly at stages of meiosis and/or early spermiogenesis.