Deficiency in the Omega-3 Fatty Acid Pathway Results in Failure of Acrosome Biogenesis in Mice1

Abstract

An omega-3 fatty acid, docosahexaenoic acid (DHA), is enriched in testicular membrane phospholipids, but its function is not well understood. The Fads2 gene encodes an enzyme required for the endogenous synthesis of DHA. Using Fads2-null mice (Fads2-/-), we found in our preceding studies that DHA deficiency caused the arrest of spermiogenesis and male infertility, both of which were reversed by dietary DHA. In this study, we investigated a cellular mechanism underlying the DHA essentiality in spermiogenesis. Periodic acid-Schiff staining and acrosin immunohistochemistry revealed the absence of acrosomes in Fads2-/- round spermatids. Acrosin, an acrosomal marker, was scattered throughout the cytoplasm of the Fads2-/- spermatids, and electron microscopy showed that proacrosomal granules were formed on the trans-face of the Golgi. However, excessive endoplasmic reticulum and vesicles were present on the cis-face of the Golgi in Fads2-/- spermatids. The presence of proacrosomal vesicles but lack of a developed acrosome in Fads2-/- spermatids suggested failed vesicle fusion. Syntaxin 2, a protein involved in vesicle fusion, colocalized with acrosin in the acrosome of wild-type mice. In contrast, syntaxin 2 remained scattered in reticular structures and showed no extensive colocalization with acrosin in the Fads2-/- spermatids, suggesting failed fusion with acrosin-containing vesicles or failed transport and release of syntaxin 2 vesicles from Golgi. Dietary supplementation of DHA in Fads2-/- mice restored an intact acrosome. In conclusion, acrosome biogenesis under DHA deficiency is halted after release of proacrosomal granules. Misplaced syntaxin 2 suggests an essential role of DHA in proper delivery of membrane proteins required for proacrosomal vesicle fusion.

t-SNARE Syntaxin2 (STX2) Is Implicated in Intracellular Transport of Sulfoglycolipids During Meiotic Prophase in Mouse Spermatogenesis

“…In wild-type germ cells, perinuclear STX2 localization suggested its presence in the Golgi apparatus or endoplasmic reticulum of spermatocytes, and in the acrosomal vesicle/acrosome of spermatids. This is consistent with a previous report [40]. We did not observe definitive localization of STX2 in the interstitial tissue, such as Leydig cells, in contrast with a previous report [9].…”

Biogenesis of sperm acrosome is regulated by pre-mRNA alternative splicing of Acrbp in the mouse

“…We next examined the acrosomal status of Acrbp −/− spermatogenic cells, using Alexa Fluor 568-conjugated peanut agglutinin (PNA) capable of binding mainly the outer acrosomal membrane (19). Consistent with already published reports (1,(20)(21)(22), a single, sphere acrosomal granule was formed in the center of the acrosomal vesicle of Acrbp +/+ spermatids by assembly of proacrosomal vesicles at steps 2 and 3 (Golgi phase) of spermiogenesis ( Fig. 2A).…”

Both maternal and offspring Elovl2 genotypes determine systemic DHA levels in perinatal mice

“…Previous studies have revealed that FADS2-ablation or dietary DHA deficiency affects fertility of both genders, as well as breeding outcomes in general (45)(46)(47)(48). In contrast to this, we observed that Elovl2 / mothers fed a DHA-enriched diet had a lower level of successful pregnancies (Table 3).…”