Hominoid-specific SPANXA/D genes demonstrate differential expression in individuals and protein localization to a distinct nuclear envelope domain during spermatid morphogenesis.

Human sperm protein associated with the nucleus on the X chromosome consists of a five-member gene family and clustered at Xq27.1. Evolved from an ancestral gene family (at Xq27 and Xp11) present in all primates as well as in rats and mice, the family is present only in humans, bonobos, chimpanzees and gorillas. Among hominoid-specific genes, the duanyu1842NXA/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 duanyu1842NXA/D genes are expressed in humans, differences are evident. In particular, duanyu1842NXC is expressed only in a subset of men. The 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 domain migrated into the base of the head as the redundant nuclear envelope that protrudes into the residual cytoplasm. Post-testicular modification of the duanyu1842NXa/d proteins was noted, as were PEST (proline, glutamic acid, serine, and threonine rich regions) domains. It is concluded that the duplication of the duanyu1842NX-N gene family that occurred 6-11 MYA resulted in a new gene family, that plays a role during spermiogenesis. The duanyu1842NXa/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.

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