GIV/Girdin Regulates Spatiotemporal Signaling during Sperm Capacitation and is Required for Male Fertility

For a sperm to successfully fertilize an egg, it must first undergo capacitation in the female reproductive tract, and later undergo acrosomal reaction (AR) upon encountering an egg. How premature AR is avoided despite rapid surges in signaling cascades during capacitation remains unknown. Using a combination of KO mice and cell-penetrating peptides, here we show that GIV (CCDC88A), a guanine nucleotide-exchange factor (GEM) for trimeric GTPases, is highly expressed in spermatocytes and is required for male fertility. GIV is rapidly phosphoregulated on key tyrosine and serine residues in human and murine sperms. These phosphomodifications enable GIV-GEM to orchestrate two distinct compartmentalized signaling programs in the sperm tail and head; in the tail, GIV enhances PI3K→Akt signals, sperm motility and survival, whereas in the head it inhibits cAMP surge and premature AR. Furthermore, GIV transcripts are downregulated in the testes and semen of infertile men. These findings exemplify the spatiotemporally segregated signaling programs that support sperm capacitation and the etiology of infertility in men. Eight-week-old conditional GIV-KO mice (Girdin fl/fl-UBC-Cre-ERT2; n = 4) or WT littermate controls (Girdin fl/fl; n = 3) were injected with Tamoxifen (i.p, 5 consecutive days), followed by co-housing with females for assessing the total number of live births over time and litter sizes. Testes were harvested at the end of study and analyzed by RNA Seq.