Asthenozoospermia in Mice with Targeted Deletion of the Sperm Mitochondrion-Associated Cysteine-Rich Protein (Smcp) Gene

Abstract

The sperm mitochondria-associated cysteine-rich protein (SMCP) is a cysteine-and proline-rich structural protein that is closely associated with the keratinous capsules of sperm mitochondria in the mitochondrial sheath surrounding the outer dense fibers and axoneme. To investigate the function of SMCP, we generated mice with a targeted disruption of the gene Smcp by homologous recombination. Homozygous mutant males on a mixed genetic background (C57BL/6J ؋ 129/Sv) are fully fertile, while they are infertile on the 129/Sv background, although spermatogenesis and mating are normal. Homozygous Smcp ؊/؊ female mice are fertile on both genetic backgrounds. Electron microscopical examination demonstrated normal structures of sperm head, mitochondria, and tail. In vivo experiments with sperm of Smcp ؊/؊ 129/Sv mice revealed that the migration of spermatozoa from the uterus into the oviduct is reduced. This result is supported by the observation that sperm motility as determined by the computer-assisted semen analysis system (CASA) is significantly affected as compared to wild-type spermatozoa. In vitro fertilization assays showed that Smcpdeficient spermatozoa are able to bind to the oocyte but that the number of fertilized eggs is reduced by more than threefold relative to the wild-type control. However, removal of the zona pellucida resulted in an unaffected sperm-egg fusion which was monitored by the presence of pronuclei and generation of blastocyts. These results indicate that the infertility of the male Smcp ؊/؊ mice on the 129/Sv background is due to reduced motility of the spermatozoa and decreased capability of the spermatozoa to penetrate oocytes.Mitochondria are confined to a structure known as the mitochondrial sheath in the midpiece of mammalian spermatozoa. The mitochondria in the sheath are elongated, crescent shaped, and aligned end-to-end in helices wrapped around the outer dense fibers which in turn surround the flagellar axoneme (21). Pallini et al. (22) purified sonication-and sodium dodecyl sulfate (SDS)-resistant structures from sperm mitochondria, known as capsules, that retain the size and shape of the outer membranes of sperm mitochondria. The integrity of capsules is maintained by disulfide bridges, and purified capsules from bull sperm contain three proteins, including a peculiar hydrophilic protein containing a large amount of proline (26%) and cysteine (18%), the sperm mitochondria-associated cysteine-rich protein (SMCP). For many years, SMCP was thought to be a 20-kDa selenoprotein and the predominant capsular protein (7), but recent work demonstrates that those attributes belong to phospholipid hydroxide glutathione peroxidase, which functions as a cytosolic enzyme in somatic cells and an enzymatically inactive structural protein in the mitochondrial capsule (33). Electron microscope immunocytochemistry localizes mouse SMCP to the outer mitochondrial membranes and intermitochondrial spaces of the mitochondrial sheath (8). Since SMCP is neither a selenoprotein nor the major capsule protein...

The expression of the testis-specific Dyrk4 kinase is highly restricted to step 8 spermatids but is not required for male fertility in mice

“…2001), Acr (Baba, Azuma et al 1994) and Smcp (Nayernia, Adham et al 2002) on head morphology (Wu, Ribar et al 2000). Recently, similar observations were made in mice with targeted disruption of the small serine/threonine kinase (SSTK) gene (Spiridonov, Wong et al 2005) which is a member of the testis-specific serine/threonine kinase (TSSK) family.…”

A multitude of genes expressed solely in meiotic or postmeiotic spermatogenic cells offers a myriad of contraceptive targets

“…These results, coupled with a search of the literature for other genes in the five clusters, show that 17 of 19 germ cell-specific genes eliminated by homologous recombination are essential for normal male fertility (Table 6, which is published as supporting information on the PNAS web site). The genes include proteases or proteins that interact with proteases (14-17), protein kinases, or proteins that interact with protein kinases (18), transcription factors (19), proteins associated with chromatin (20)(21)(22), channels or transporters (1, 23), mitochondrial-associated proteins (24,25), adhesion proteins (26), RNA polymerases (27), and genes involved in the interaction between spermatids and Sertoli cells (28). More than 50% of these genes result in a complete loss of fertility when disrupted.…”

Transcriptome profiling of the developing postnatal mouse testis using next-generation sequencing

“…The transition nuclear proteins (TNP) constitute 90% of the chromatin basic proteins, replacing the histones temporarily, and are then switched by protamines (PRM) during spermiogenesis [52]. Smcp and Ropn1l affect sperm motility [53,54], while genes such as Tnp1, Tnp2, Prm1, Prm2, and Smcp are transcribed in round spermatids, but when spermatids undergo nuclear condensation and elongation, their mRNAs are stored in a translationally repressed state in early elongating spermatids [55][56][57][58]. Therefore, these genes can be detected as early as PN2, before elongating spermatids appear.…”