SPAG8

The correlation of anti-sperm antibodies with cases of unexplained infertility implicates a role for these antibodies in blocking fertilization. Improved diagnosis and treatment of immunologic infertility, as well as identification of proteins for targeted contraception, are dependent on the identification and characterization of relevant sperm antigens. The protein encoded by this gene is recognized by sperm agglutinating antibodies from an infertile woman. This protein is localized in germ cells of the testis at all stages of spermatogenesis and is localized to the acrosomal region of mature spermatozoa. Alternatively spliced variants that encode different protein isoforms have been described but the full-length sequences of only two have been determined. [provided by RefSeq]

Full Name

sperm associated antigen 8

Function

Plays a role in spermatogenesis by enhancing the binding of CREM isoform tau to its coactivator FHL5 and increasing the FHL5-regulated transcriptional activation of CREM isoform tau (By similarity).
Involved in the acrosome reaction and in binding of sperm to the zona pellucida (By similarity).
Plays a role in regulation of the cell cycle by controlling progression through the G2/M phase, possibly by delaying the activation of CDK1 which is required for entry into mitosis (PubMed:19548270).
May play a role in fertility and microtubule formation through interaction with RANBP9 (PubMed:10500252).

Biological Process

Biological Process cell cycleIEA:UniProtKB-KW
Biological Process cell differentiationIEA:UniProtKB-KW
Biological Process positive regulation of protein bindingIEA:Ensembl
Biological Process positive regulation of transcription by RNA polymerase IIManual Assertion Based On ExperimentIBA:GO_Central
Biological Process single fertilizationIEA:UniProtKB-KW
Biological Process spermatogenesisIEA:UniProtKB-KW

Cellular Location

Cytoplasm
Nucleus
Cytoplasmic vesicle, secretory vesicle, acrosome
Cytoplasm, cytoskeleton, microtubule organizing center
Cytoplasm, cytoskeleton, spindle
Cytoplasm, cytoskeleton, cilium axoneme
In mature sperm cells, detected in the acrosomal region of the head and in the middle piece of the tail (By similarity).
Localized to the nucleus and cytoplasm of spermatocytes and round spermatids while, in elongating spermatids, expressed in the cytoplasm but not in the nucleus (By similarity).
During the cell cycle, localized on the microtubule-organizing center (MTOC) during prophase. In metaphase, extends along spindle microtubules. In anaphase, detected on the astral microtubules and mid-zone. In telophase, remains at the mid-zone. After cytokinesis, returns to the MTOC (PubMed:19548270).
Microtubule inner protein (MIP) part of the dynein-decorated doublet microtubules (DMTs) in cilia axoneme (By similarity).