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Mol. Hum. Reprod. Advance Access originally published online on September 29, 2006
Molecular Human Reproduction 2006 12(11):703-716; doi:10.1093/molehr/gal079
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© The Author 2006. Published by Oxford University Press on behalf of the European Society of Human Reproduction and Embryology. All rights reserved. For Permissions, please email: journals.permissions@oxfordjournals.org
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Hominoid-specific SPANXA/D genes demonstrate differential expression in individuals and protein localization to a distinct nuclear envelope domain during spermatid morphogenesis

V.A. Westbrook1,2, P.D. Schoppee1, G.R. Vanage1,3, K.L. Klotz1, A.B. Diekman1,4, C.J. Flickinger1, M.A. Coppola1 and J.C. Herr1,5

1Department of Cell Biology, Center for Research in Contraceptive and Reproductive Health, University of Virginia, Charlottesville, VA, USA

2 Present address: Department of Biochemistry and Molecular Genetics, University of Virginia, Box 800733, Charlottesville, VA 22908, USA

3 Present address: Institute for Research in Reproduction, Mumbai, India

4 Present address: Department of Biochemistry and Molecular Biology, University of Arkansas for Medical Sciences, 4301 West Markham Street, Slot 516, Little Rock, AR 72205, USA

5 To whom correspondence should be addressed at: Department of Cell Biology, Center for Research in Contraceptive and Reproductive Health, University of Virginia, Box 800732, 1300 Jefferson Park Avenue, Charlottesville, VA 22908, USA. E-mail: jch7k{at}virginia.edu

Human sperm protein associated with the nucleus on the X chromosome consists of a five-member gene family (SPANXA1, SPANXA2, SPANXB, SPANXC and SPANXD) clustered at Xq27.1. Evolved from an ancestral SPANX-N gene family (at Xq27 and Xp11) present in all primates as well as in rats and mice, the SPANXA/D family is present only in humans, bonobos, chimpanzees and gorillas. Among hominoid-specific genes, the SPANXA/D gene family is considered to be undergoing rapid positive selection in its coding region. In this study, RT–PCR of human testis mRNA from individuals showed that, although all SPANXA/D genes are expressed in humans, differences are evident. In particular, SPANXC is expressed only in a subset of men. The SPANXa/d protein localized to the nuclear envelope of round, condensing and elongating spermatids, specifically to regions that do not underlie the developing acrosome. During spermiogenesis, the SPANXa/d-positive domain migrated into the base of the head as the redundant nuclear envelope that protrudes into the residual cytoplasm. Post-testicular modification of the SPANXa/d proteins was noted, as were PEST (proline, glutamic acid, serine, and threonine rich regions) domains. It is concluded that the duplication of the SPANX-N gene family that occurred 6–11 MYA resulted in a new gene family, SPANXA/D, that plays a role during spermiogenesis. The SPANXa/d gene products are among the few examples of X-linked nuclear proteins expressed following meiosis. Their localization to non-acrosomal domains of the nuclear envelope adjacent to regions of euchromatin and their redistribution to the redundant nuclear envelope during spermiogenesis provide a biomarker for the redundant nuclear envelope of spermatids and spermatozoa.

Key words: cancer/hominoids/spermatozoa/spermiogenesis/testis


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