Galnt3 deficiency disrupts acrosome formation and leads to oligoasthenoteratozoospermia

Abstract

Galnt3 belongs to the GalNAc transferase gene family involved in the initiation of mucin-type O-glycosylation. Male Galnt3-deficient (Galnt3(-/-)) mice were infertile, as previously reported by Ichikawa et al. (2009). To investigate the involvement of Galnt3 in spermatogenesis, we examined the differentiation of germ cells in Galnt3(-/-) mice. Galnt3 mRNA was most highly expressed in testis, and Galnt3 protein was localized in the cis-medial parts of the Golgi stacks of spermatocytes and spermatids in the seminiferous tubules. Spermatozoa in Galnt3(-/-) mice were rare and immotile, and most of them had deformed round heads. They exhibited abnormal acrosome and disturbed mitochondria arrangement in the flagella. At the cap phase, proacrosomal vesicles of various sizes, which had not coalesced to form a single acrosomal vesicle, were attached to the nucleus in Galnt3(-/-) mice. TUNEL-positive cells were increased in the seminiferous tubules. The binding of VVA lectin, which recognizes the Tn antigen (GalNAc-O-Ser/Thr), in the acrosomal regions of spermatids and spermatozoa in Galnt3(-/-) mice was drastically reduced. Equatorin is a N, O-sialoglycoprotein localized in the acrosomal membrane and is suggested to be involved in sperm-egg interaction. Immunohistochemical and Western blot analyses showed a drastic reduction in the reactivity with MN9 antibody, which recognizes the O-glycosylated moiety of equatorin and inhibits sperm-egg interaction. These findings indicate that deficiency of Galnt3 results in a severe reduction of mucin-type O-glycans in spermatids and causes impaired acrosome formation, leading to oligoasthenoteratozoospermia, and suggest that Galnt3 may also be involved in the process of fertilization through the O-glycosylation of equatorin.

Influenza A Virus-Induced Expression of a GalNAc Transferase, GALNT3, via MicroRNAs Is Required for Enhanced Viral Replication

“…The posttranslational glycosylation of FGF23 by GALNT3 results in the prevention of FGF23 proteinase processing (52), suggesting that GALNT3 is important for controlling the pathophysiological level of FGF23 (53,54). Although galnt3-KO mice exhibit testicular calcifications and male infertility (30), it is unlikely that FGF23 is directly involved in the replication of IAV due to the fact that the expression of FGF23 has not been demonstrated in respiratory epithelial cells. However, a recent study revealed that GALNT3 suppression results in the up-or downregulation of numerous genes associated with the pathways involved in transcriptional regulation, signal transduction, cell proliferation, immune and inflammatory responses, and mucin O-glycosylation modification in epithelial ovarian cancer cells, demonstrating that GALNT3 contributes to various cellular processes through the O-glycosylation of many unknown substrates (55).…”

The Acrosomal Matrix

“…Mutations affecting SEC23IP, a phospholipase A1-like protein that interacts with Sec23, also cause male subfertility by interfering with acrosome biogenesis and leading to round-headed spermatozoa (Arimitsu et al 2011). Spermatids of infertile male mice lacking GalNAc transferase 3 (GALNT3) produce proacrosomal vesicles of various sizes, which attach to the nuclear envelope but do not coalesce to form a single acrosomal vesicle, apparently causing oligoasthenoteratozoospermia through a severe reduction of mucin-type O-glycans, impaired acrosome formation, and increased apoptosis (Miyazaki et al 2012). Acrosomal dysplasia does occur in cases where certain acrosomal matrix components such as zona pellucida-binding protein 1 (ZPBP) or 2 (ZPBP2) are missing (Lin et al 2007).…”

Equatorin-Related Subcellular and Molecular Events During Sperm Priming for Fertilization in Mice

“…Galnt3-null mouse homozygotic testicular germ cells exhibit drastically reduced reactivity with the MN9 antibody, and the mice are infertile because of oligoashthenoteratozoospermia (Miyazaki et al 2013 ). In these mutant mice, spermatozoa are rare in the cauda epididymides, most of which exhibit deformed rounded heads.…”

“…Galnt3 is a GalNAc transferase family protein involved in the initiation of mucin-type O -glycosylation (Bennett et al 1996 ). The VVA ( Vicia villosa agglutinin) lectin, which can recognize the Tn antigen (GalNAc-O-Ser/Thr) generated by GalNac transferase, also recognizes the acrosomal regions of spermatids and spermatozoa, whereas VVA binding is drastically reduced in Galnt3-null mice (Miyazaki et al 2013 ). Thus, GlcNAcβ1-3-GalNAcα1-Ser/Thr mediated by Galnt3 (GalNAc transferase) is involved in the formation of the equatorin epitope region recognized by the MN9 antibody.…”