A missense mutation in the Capza3 gene and disruption of F-actin organization in spermatids of repro32 infertile male mice

Abstract

Males homozygous for the repro32 ENU-induced mutation produced by the Reproductive Genomics program at The Jackson Laboratory are infertile, have low epididymal sperm concentrations, and produce sperm with abnormally shaped heads and poor motility. The purpose of the present study was to identify the mutated gene in repro32 mice and to define the structural and functional changes causing infertility and the aberrant sperm phenotype. In repro32/repro32 mice, we discovered a failure to shed excess cytoplasm and disorganization of the middle piece of the flagellum at spermiation, resulting in the outer dense fibers being wrapped around the sperm head within a bag of cytoplasm. Using a candidate-gene approach, a mutation was identified in the spermatid-specific “capping protein (actin filament) muscle Z-line, alpha 3” gene (Capza3). CAPZA3 protein localization was altered in spermatids concurrent with altered localization of a unique CAPZB variant isoform and disruption of the filamentous actin (F-actin) network. These observations strongly suggest the missense mutation in Capza3 is responsible for the mutant phenotype of repro32/repro32 sperm and regulation of F-actin dynamics by a spermatogenic cell-specific CAPZ heterodimer is essential for removal of the cytoplasm and maintenance of midpiece integrity during spermiation in the mouse.

PLCζ sequence, protein levels, and distribution in human sperm do not correlate with semen characteristics and fertilization rates after ICSI

“…The role of this long noncoding RNA is unknown, although it is located at 5′ UTR of CAPZA3 (capping protein (actin filament) muscle Zline, alpha 3), which is localized in the sperm acrosome and plays a role in maintaining polymerized actin during spermatogenesis [36]. Although disruptions in the CAPZA3 protein have been clearly linked to male infertility in mice [37], where the report32 mutated mice, identified in the course of an ENU mutagenesis screen, present disruption of F-actin, the role of lncCAPZA3-1.1 and its SNP variants has not been evaluated yet in male infertility and deserves further exploration. Both samples from low fertilization cycles (<20 %) and TFF cycles displayed the presence of the same SNPs.…”

Spermiation

“…The retention and phagocytosis of spermatids within Sertoli cells has not been described in these mice, however, there is evidence to suggest that spermatids with abnormal cytoplasm persist longer in the epithelium, into stage IX, before eventually being released. 106 This fascinating phenotype points to two novel concepts: (1) that a delay of disengagement may be possible, as the Sertoli cell tries unsuccessfully to remodel the abnormal spermatid (contradicting earlier reviews stating that such a delay is unlikely 1 ) and (2) that the spermatid may influence its own ability to undergo successful spermiation.…”

“…For example, a missense mutation in the Capza3 gene in mice results in infertility due to abnormal sperm morphology and a failure to shed excess cytoplasm during spermiation. 106 Capza3 is localized in elongated spermatid cytoplasm and is an actin-capping protein involved in the regulation of F-actin dynamics. Spermatids within the Capza3 mutant epididymis have a "bag" of excess cytoplasm around their heads, together with other flagellar and structural abnormalities that likely arose earlier in the spermiogenic process.…”

Mouse models in male fertility research

“…45 Such programs have revealed many critical genes for human diseases, including male infertility. [46][47][48][49] …”