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 (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.
Westbrook
V A
VA
Department of Cell Biology, Center for Research in Contraceptive and Reproductive Health, University of Virginia, Charlottesville, VA 22908, USA.
Schoppee
P D
PD
Vanage
G R
GR
Klotz
K L
KL
Diekman
A B
AB
Flickinger
C J
CJ
Coppola
M A
MA
Herr
J C
JC
D000177:Acrosome / Q000648:ultrastructure; D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D000818:Animals; D002451:Cell Compartmentation; D041321:Chromosomes, Human, X / Q000235:genetics; D016384:Consensus Sequence; D022041:Euchromatin / Q000648:ultrastructure; D019143:Evolution, Molecular; D019084:Fluorescent Antibody Technique, Indirect; D020440:Gene Duplication; D018507:Gene Expression Regulation, Developmental; D006801:Humans; D007206:Individuality; D008297:Male; D008540:Meiosis; D008854:Microscopy, Electron; D008969:Molecular Sequence Data; D009024:Morphogenesis / Q000235:genetics; D009363:Neoplasm Proteins / Q000096:biosynthesis / Q000235:genetics*; D009685:Nuclear Envelope / Q000378:metabolism* / Q000648:ultrastructure; D009687:Nuclear Proteins / Q000096:biosynthesis / Q000235:genetics* / Q000378:metabolism; D002679:Pan troglodytes / Q000378:metabolism*; D010802:Phylogeny; D011323:Primates / Q000378:metabolism; D017434:Protein Structure, Tertiary; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D013045:Species Specificity; D013087:Spermatids / Q000378:metabolism* / Q000648:ultrastructure; D013091:Spermatogenesis / Q000235:genetics*; D014158:Transcription, Genetic; D014960:X Chromosome / Q000235:genetics
D022041:Euchromatin; D009363:Neoplasm Proteins; D009687:Nuclear Proteins; C414403:SPANXA1 protein, human; C521014:SPANXA2 protein, human; C518957:SPANXB1 protein, human; C403097:SPANXC protein, human; C521016:SPANXD protein, human