Ca2+/calmodulin-dependent protein kinase IV (Camk4; also known as CaMKIV), a multifunctional serine/threonine protein kinase with limited tissue distribution, has been implicated in transcriptional regulation in lymphocytes, neurons and male germ cells1,2,3,4,5,6. In the mouse testis, however, Camk4 is expressed in spermatids and associated with chromatin and nuclear matrix7. Elongating spermatids are not transcriptionally active8, raising the possibility that Camk4 has a novel function in male germ cells. To investigate the role of Camk4 in spermatogenesis, we have generated mice with a targeted deletion of the gene Camk4. Male Camk4−/− mice are infertile with impairment of spermiogenesis in late elongating spermatids. The sequential deposition of sperm basic nuclear proteins on chromatin is disrupted, with a specific loss of protamine-2 and prolonged retention of transition protein-2 (Tnp2) in step-15 spermatids. Protamine-2 is phosphorylated by Camk4 in vitro, implicating a connection between Camk4 signalling and the exchange of basic nuclear proteins in mammalian male germ cells. Defects in protamine-2 have been identified in sperm of infertile men, suggesting that our results may have clinical implications for the understanding of human male infertility.
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We thank R. Balhorn for the protamine antibodies; S. Kistler for the Tnp2 antibody; C. Bock for the generation of the mutant mice; A. Nagy, R. Nagy and W. Abramow-Newerly for the use of R1 ES cells; and X.F. Wang, Y. Zhuang, E. Linney and E.M. Eddy for helpful discussions. This work was supported by an N.I.H. Medical Scientist Training Program award to J.Y.W. and N.I.H. grant HD07503 to A.R.M.
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Wu, J., Ribar, T., Cummings, D. et al. Spermiogenesis and exchange of basic nuclear proteins are impaired in male germ cells lacking Camk4. Nat Genet 25, 448–452 (2000). https://doi.org/10.1038/78153
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