Sperm-oocyte contact induces outside-in signaling via PYK2 activation

Abstract

Fertilization is a multi-step process that begins with plasma membrane interactions that enable sperm - oocyte binding followed by fusion of the sperm and oocyte plasma membranes. Once membrane fusion has occurred, sperm incorporation involves actin remodeling events within the oocyte cortex that allow the sperm head to penetrate the cortical actin layer and gain access to the ooplasm. Despite the significance for reproduction, the control mechanisms involved in gamete binding, fusion, and sperm incorporation are poorly understood. While it is known that proline - rich tyrosine kinase 2 (PYK2 or PTK2b) kinase activity plays an important role in fertilization, its specific function has not been addressed. The present study made use of a zona-free mouse oocyte fertilization assay to investigate the relationship between PYK2 activity and sperm - oocyte binding and fusion, as well as localized changes in actin polymerization and sperm incorporation. In this assay, the majority of bound sperm had no apparent effect on the oocyte and only a few became incorporated into the ooplasm. However, a subset of bound sperm were associated with a localized response in which PYK2 was recruited to the oocyte cortex where it frequently co-localized with a ring or disk of f-actin. The frequency of sperm-oocyte binding sites that exhibited this actin response was reduced in pyk2−/− oocytes and the pyk2−/− oocytes proved less efficient at incorporating sperm, indicating that this protein kinase may have an important role in sperm incorporation. The response of PYK2 to sperm-oocyte interaction appeared unrelated to gamete fusion since PYK2 was recruited to sperm - binding sites under conditions where sperm - oocyte fusion was prevented and since PYK2 suppression or ablation did not prevent sperm - oocyte fusion. While a direct correlation between the PYK2 response in the oocyte and the successful incorporation of individual bound sperm remains to be established, these findings suggest a model in which the oocyte is not a passive participant in fertilization, but instead responds to sperm contact by localized PYK2 signaling that promotes actin remodeling events required to physically incorporate the sperm head into the ooplasm.

Silencing Nogo-B receptor inhibits penile corpus cavernosum vascular smooth muscle cell apoptosis of rats with diabetic erectile dysfunction by down-regulating ICAM-1

“…[33] PYK2 plays an important role in sexual function such as sperm incorporation by being recruited to the oocyte cortex, incorporating the sperm head via actin and responding to sperm binding. [34] Allingham MJ et al . investigated the function of tyrosine phosphorylation in the mediation of junctions during leukocyte transendothelial migration and found that ICAM-1 is involved in the mediation of SRC- and PYK2-dependent vascular endothelial cadherin tyrosine phosphorylation.…”

Ptk2b deletion improves mice folliculogenesis and fecundity via inhibiting follicle loss mediated by Erk pathway

“…In females, it has also been reported to be localized to microtubule organizing center or concentrated in cortical cytoskeleton of the oocytes, and played important roles in spindle assembly (Meng et al, 2018) or oocyte maturation (Meng et al, 2006). Moreover, some other studies also found that Ptk2b functioned during fertilization (McGinnis, Luo, & Kinsey, 2013; Meng et al, 2016) and the Ptk2b disruption prevented the incorporation of sperm to the ooplasm (Luo, McGinnis, Carlton, Beggs, & Kinsey, 2014; Wang, Luo, Carlton, McGinnis, & Kinsey, 2017). However, all the studies above were performed in vitro, in vivo validation of its exact reproductive relative biological functions, especially in folliculogenesis is still missing.…”

“…Ptk2b disruption prevented the incorporation of sperm to the ooplasm (Luo, McGinnis, Carlton, Beggs, & Kinsey, 2014;Wang, Luo, Carlton, McGinnis, & Kinsey, 2017). However, all the studies above were performed in vitro, in vivo validation of its exact reproductive relative biological functions, especially in folliculogenesis is still missing.…”

Preventing polyspermy in mammalian eggs—Contributions of the membrane block and other mechanisms

“…In mammals, it is now known that the "fusion hypothesis" describes how egg activation occurs—sperm−egg fusion precedes and is required for egg activation, and leads to the release of PLCζ from the sperm into the egg cytoplasm (Hachem et al, 2017; Lawrence, Whitaker, & Swann, 1997). Although PLCζ‐initiated calcium transients appear to be the key trigger for nearly all egg activation responses, recent data suggest that sperm−egg adhesion can induce some cellular changes in the egg, including localized remodeling of actin in the egg cortex (Wang, Luo, Carlton, McGinnis, & Kinsey, 2017). The egg actomyosin cytoskeleton is a potential mediator of the membrane block, based on data from mice (Mackenzie et al, 2016; McAvey et al, 2002), and similarly, the surf clam Spisula has a persistent membrane block (in addition to a transient electrical block) that is impaired by actin perturbation and is not mediated by cortical granule exocytosis (Longo, 1976; Ziomek & Epel, 1975).…”