Complexin-I-deficient sperm are subfertile due to a defect in zona pellucida penetration

Abstract

Upon adhesion to the zona pellucida, sperm undergo regulated exocytosis of the acrosome. Although it is necessary for sperm to penetrate the zona pellucida and fertilize an egg, the acrosomal membrane fusion process is poorly understood. Complexins I and II are small, cytosolic proteins that bind to a complex of proteins termed the soluble N-ethylmaleimide-sensitive factor attachment protein receptor complex to regulate synaptic vesicle exocytosis. Complexin-II-deficient mice are fertile but the fertility of sperm from complexin-I-deficient male mice is unclear because the mice have ataxia and cannot mate. Here, we show that the genes encoding complexins I and II are expressed in primary spermatocytes and spermatids. Complexin proteins were found in/near the developing acrosome in spermatids and in or around the acrosome of mature sperm. Cell fractionation demonstrated that complexins I and II were predominantly found in the cytosolic fraction. Furthermore, sperm from complexin-I-deficient mice had normal morphology, number, and only small differences in motility, as assessed by computer-assisted semen analysis. Complexin-I-deficient sperm capacitated normally and bound to the zona pellucida. But when sperm from complexin-I-deficient mice were inseminated into females, a defect in fertility was observed, in concordance with previous data showing that in vitro fertilization rate was also reduced. If the zona pellucida was removed prior to in vitro fertilization, fertility was normal, demonstrating that zona pellucida penetration was defective, a step requiring acrosomal exocytosis. Therefore, complexin-I-deficient sperm are subfertile due to faulty zona pellucida penetration.

Sperm from Hyh Mice Carrying a Point Mutation in αSNAP Have a Defect in Acrosome Reaction

“…Enzymes present in the acrosomal granule must be released to facilitate sperm penetration through the zona pellucida. Hence, it would be expected that malfunctions in factors necessary for secretion would affect the fertilizing potential of sperm [24], [25]. However, since secretion is a key cellular function necessary for many survival mechanisms, most mutations in these factors render animals unable to survive to reproductive age.…”

Surfing the wave, cycle, life history, and genes/proteins expressed by testicular germ cells. Part 2: Changes in spermatid organelles associated with development of spermatozoa

“…Dynamin 2 may play a role during acrosome formation and/or acrosomal exocytosis (Zhao et al, 2007b). Complexin II-deficient mice are fertile, and while sperm from complexin I-deficient mice have normal morphology, numbers and small differences in motility, they are defective in zona pellucida penetration, a step requiring acrosomal exocytosis (Zhao et al, 2007a(Zhao et al, , 2008. CASK [ID: T2-268] is an adaptor protein regulating exocytosis.…”

Genome-Wide Association Study Implicates Testis-Sperm Specific FKBP6 as a Susceptibility Locus for Impaired Acrosome Reaction in Stallions

“…The process is known as regulated acrosomal exocytosis or acrosomal reaction (AR) and is triggered by egg's zona pellucida proteins which induce an influx of calcium in to the sperm. Acrosomal exocytosis facilitates the passage of the sperm through the zona and is obligatory for natural fertilization [1], [2], [3], [4], [5]. The AR is a one-time event during which the acrosome releases all its contents and loses structural integrity [2].…”