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Meiotic Expression of the Cyclin H/Cdk7 Complex in Male Germ Cells of the Mouse¹

^a Department of Cell Biology & Biochemistry, Texas Tech University Health Sciences Center, Lubbock, Texas 79430

ABSTRACT

Cell division requires that cyclin-dependent kinases (Cdks) be activated by phosphorylation. In mitotic cells, this is accomplished by the Cdk-activating-kinase (CAK), which is a complex of cyclin H and Cdk7. There are currently no data on the role of CAK in meiotic cells. Previously, we have shown that cyclin A1 is meiosis-specific and forms an active kinase with Cdk2. Because cyclin A1 is required for meiosis, and its associated kinase must be phosphorylated (activated), we propose that cyclin H/Cdk7 function to activate cyclin A1/Cdk2 in meiotic cells. Here, we show that cyclin H and Cdk7 are present during meiosis. Using reverse transcription-polymerase chain reaction and in situ hybridization, we show that the mRNAs encoding cyclin H and Cdk7 are abundant in spermatocytes. Immunohistochemistry localized cyclin H and Cdk7 to the nucleus of spermatocytes in stages IV to XII of the spermatogenic cycle, overlapping the same stages that express cyclin A1-associated kinases. Finally, immunoprecipitation and histone H1-kinase assays of cyclin H and Cdk7 from testicular extracts show that these proteins interact to form an active kinase. We conclude that cyclin H/Cdk7 complexes are present and during meiosis, form active complexes in testicular cells and are strong candidates for the activating kinase for cyclin A1-associated kinase.

FOOTNOTES

First decision: 12 October 2000.

¹ These studies were supported by grants from the South Plains Foundation, TTUHSC Seed Research Grant program, and National Institutes of Health HD36285 to S.E.R. Additional support to J.M.K., J.T.M., and R.K.B. was provided, in part, by a grant from the Howard Hughes Medical Institute through the Undergraduate Biological Sciences Education Program at Texas Tech University.

² Correspondence. FAX: 806 743 2990; cbbser{at}ttuhsc.edu

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