title: Meiotic expression of the cyclin H/Cdk7 complex in male germ cells of the mouse.
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.
authors.affiliation: Department of Cell Biology & Biochemistry, Texas Tech University Health Sciences Center, Lubbock, Texas 79430, USA.
authors.forename: J M
authors.initials: JM
authors.lastname: Kim
authors.forename: J T
authors.initials: JT
authors.lastname: McGaughy
authors.forename: R K
authors.initials: RK
authors.lastname: Bogle
authors.forename: S E
authors.initials: SE
authors.lastname: Ravnik
mesh_terms: D000818:Animals; D002467:Cell Nucleus / Q000737:chemistry; D003001:Cloning, Molecular; D056748:Cyclin H; D018844:Cyclin-Dependent Kinases; D016213:Cyclins / Q000032:analysis / Q000235:genetics* / Q000502:physiology; D015870:Gene Expression; D007150:Immunohistochemistry; D007163:Immunosorbent Techniques; D017403:In Situ Hybridization; D008297:Male; D008540:Meiosis; D051379:Mice; D008817:Mice, Mutant Strains; D017346:Protein Serine-Threonine Kinases / Q000032:analysis / Q000235:genetics* / Q000502:physiology; D012333:RNA, Messenger / Q000032:analysis; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012708:Sertoli Cells / Q000737:chemistry; D013091:Spermatogenesis; D013094:Spermatozoa / Q000737:chemistry* / Q000648:ultrastructure; D013737:Testis / Q000737:chemistry / Q000254:growth & development; D000095043:Cyclin-Dependent Kinase-Activating Kinase
chemical_list: D056748:Cyclin H; D018844:Cyclin-Dependent Kinases; D016213:Cyclins; D017346:Protein Serine-Threonine Kinases; D012333:RNA, Messenger; D000095043:Cyclin-Dependent Kinase-Activating Kinase; C534752:Ccnh protein, mouse; C090586:Cdk7 protein, mouse