Differential distribution of ganglioside GM3 in seminiferous tubule and epididymis of adult rats

Role of sphingolipid metabolites in the homeostasis of steroid hormones and the maintenance of testicular functions

With the acceleration of life pace and the increase of work pressure, the problem of male infertility has become a social problem of general concern. Sphingolipids are important regulators of many cellular processes like cell differentiation and apoptosis, which are ubiquitously expressed in all mammalian cells. Various sphingolipid catabolic enzymes can generate multiple sphingolipids like sphingosine-1-phosphate and sphingomyelin. Present studies have already demonstrated the role of steroid hormones in the physiological processes of reproduction and development through hypothalamus-pituitary-gonad axis, while recent researches also found not only sphingolipids can modulate steroid hormone secretion, but also steroid hormones can control sphingolipid metabolites, indicating the role of sphingolipid metabolites in the homeostasis of steroid hormones. Furthermore, sphingolipid metabolites not only contribute to the regulation of gametogenesis, but also mediate damage-induced germ apoptosis, implying the role of sphingolipid metabolites in the maintenance of testicular functions. Together, sphingolipid metabolites are involved in impaired gonadal function and infertility in males, and further understanding of these bioactive sphingolipids will help us develop new therapeutics for male infertility in the future.

Lipid Signaling During Gamete Maturation

Cell lipids are differentially distributed in distinct organelles and within the leaflets of the bilayer. They can further form laterally defined sub-domains within membranes with important signaling functions. This molecular and spatial complexity offers optimal platforms for signaling with the associated challenge of dissecting these pathways especially that lipid metabolism tends to be highly interconnected. Lipid signaling has historically been implicated in gamete function, however the detailed signaling pathways involved remain obscure. In this review we focus on oocyte and sperm maturation in an effort to consolidate current knowledge of the role of lipid signaling and set the stage for future directions.

Effects of Gangliosides on Spermatozoa, Oocytes, and Preimplantation Embryos

Gangliosides are sialic acid-containing glycosphingolipids, which are the most abundant family of glycolipids in eukaryotes. Gangliosides have been suggested to be important lipid molecules required for the control of cellular procedures, such as cell differentiation, proliferation, and signaling. GD1a is expressed in interstitial cells during ovarian maturation in mice and exogenous GD1a is important to oocyte maturation, monospermic fertilization, and embryonic development. In this context, GM1 is known to influence signaling pathways in cells and is important in sperm-oocyte interactions and sperm maturation processes, such as capacitation. GM3 is expressed in the vertebrate oocyte cytoplasm, and exogenously added GM3 induces apoptosis and DNA injury during in vitro oocyte maturation and embryogenesis. As a consequence of this, ganglioside GT1b and GM1 decrease DNA fragmentation and act as H2O2 inhibitors on germ cells and preimplantation embryos. This review describes the functional roles of gangliosides in spermatozoa, oocytes, and early embryonic development.

Histochemical identification of sialylated glycans in Xenopus laevis testis

Carbohydrate chains of glycoprotein and glycosphingolipids are highly diverse molecules involved in many cell functions, including cell recognition, adhesion and signalling. Sialylated glycans are of special interest because the terminal position of sialic acid (NeuAc) in glycans linked by different ways to subterminal monosaccharides has been shown to be involved in several biological processes, as occurs with gangliosides, which have been reported as being essential in spermatogenesis in mammals. Some glycan-binding proteins, the lectins, which specifically recognize glycan sequences, have been extensively used to characterize tissue and cell carbohydrates by means of cytochemical techniques. The aim of the present work was to determine the presence of NeuAc by means of histochemical techniques in the testis of Xenopus laevis, an animal model widely used in cell and molecular biology research. However, considering that some NeuAc-binding lectins are capable of binding to N-acetylglucosamine (GlcNAc), other GlcNAc-binding lectins were also assayed. The results showed that NeuAc is mainly expressed in the interstitium, and only a weak labelling in the male germ cells was observed. Most NeuAc was located in O-linked oligosaccharides, but some masked NeuAc in N-glycans were identified in primary and secondary spermatogonia and spermatocytes. By contrast, GlcNAc was widely expressed in all germ cell types. Deglycosylative pre-treatments suggest that both N- and O-glycans and/or glycolipids could be responsible for this labelling. In addition, GlcNAc in O-linked oligosaccharides has been identified in spermatogonial cells. The acrosome of spermatids was always negative. Variations of glycan expression have been found in different cell types, suggesting that glycosylation is modified during spermatogenetic development.

Roles of gangliosides in mouse embryogenesis and embryonic stem cell differentiation

Gangliosides have been suggested to play important roles in various functions such as adhesion, cell differentiation, growth control, and signaling. Mouse follicular development, ovulation, and luteinization during the estrous cycle are regulated by several hormones and cell-cell interactions. In addition, spermatogenesis in seminiferous tubules of adult testes is also regulated by several hormones, including follicle-stimulating hormone (FSH) and luteinizing hormone (LH) and cell-cell interactions. The regulation of these processes by hormones and cell-cell interactions provides evidence for the importance of surface membrane components, including gangliosides. During preimplantation embryo development, a mammalian embryo undergoes a series of cleavage divisions whereby a zygote is converted into a blastocyst that is sufficiently competent to be implanted in the ma ternal uterus and continue its development. Mouse embryonic stem (mES) cells are pluripotent cells derived from mouse embryo, specifically, from the inner cell mass of blastocysts. Differentiated neuronal cells are derived from mES cells through the formation of embryonic bodies (EBs). EBs recapitulate many aspects of lineage-specific differentiation and temporal and spatial gene expression patterns during early embryogenesis. Previous studies on ganglioside expression during mouse embryonic development (including during in vitro fertilization, ovulation, spermatogenesis, and embryogenesis) reported that gangliosides were expressed in both undifferentiated and differentiated (or differentiating) mES cells. In this review, we summarize some of the advances in our understanding of the functional roles of gangliosides during the stages of mouse embryonic development, including ovulation, spermatogenesis, and embryogenesis, focusing on undifferentiated and differentiated mES cells (neuronal cells).

Localization of low-density detergent-resistant membrane proteins in intact and acrosome-reacted mouse sperm

Mammalian sperm become fertile after completing capacitation, a process associated with cholesterol loss and changes in the biophysical properties of the sperm membranes that prepares the sperm to undergo the acrosome reaction. Different laboratories have hypothesized that cholesterol efflux can influence the extent and/or movement of lipid raft microdomains. In a previous study, our laboratory investigated the identity of sperm proteins putatively associated with rafts. After extraction with Triton X-100 and ultracentrifugation in sucrose gradients, proteins distributing to the light buoyant-density fractions were cored from polyacrylamide gels and microsequenced. In this study, a subset of these proteins (TEX101, basigin, hexokinase 1, facilitated glucose transporter 3, IZUMO, and SPAM1) and other molecules known to be enriched in membrane rafts (caveolin 2, flotillin 1, flotillin 2, and the ganglioside GM3) were selected to investigate their localization in the sperm and their behavior during capacitation and the acrosome reaction. These molecules localize to multiple sperm domains, including the acrosomal cap (IZUMO, caveolin 2, and flotillin 2), equatorial segment (GM3), cytoplasmic droplet (TEX101), midpiece (basigin, facilitated glucose transporter 3, and flotillin 2), and principal piece (facilitated glucose transporter 3). Some of these markers modified their immunofluorescence pattern after sperm incubation under capacitating conditions, and these changes correlated with the occurrence of the acrosome reaction. While GM3 and caveolin 2 were not detected after the acrosome reaction, flotillin 2 was found in the equatorial segment of acrosome-reacted sperm, and IZUMO distributed along the sperm head, reaching the post- and para-acrosomal areas. Taking into consideration the requirement of the acrosome reaction for sperm to become fusogenic, these results suggest that membrane raft dynamics may have a role in sperm-egg membrane interaction.

Involvement of nitric oxide duringin vitro fertilization and early embryonic development in mice

Nitric oxide (NO) has emerged as an important intracellular and intercellular messenger, controlling many physiological processes and participating in the fertilization process via the autocrine and paracrine mechanisms. This study investigated whether nitric oxide synthase (NOS) inhibitior (L-NAME) and L-arginine could regulate in vitro fertilization and early embryonic development in mice. Mouse epididymal spermatozoa, oocytes, and embryos were incubated in mediums of variable conditions with and without L-NAME or L-arginine (0.5, 1, 5 and 10 mM). Fertilization rate and early embryonic development were significantly inhibited by treating sperms or oocytes with L-NAME (93. 8% vs 66.3%, 92.1% vs 60.3%), but not with L-arginine. In contrast, fertilization rate and early embryonic development were conspicuously reduced when L-NAME or L-arginine was added to the culture media for embryos. Early embryonic development was inhibited by microinjection of L-NAME into the fertilized embryos in a dose-dependent manner, but only by high concentrations of L-arginine. These results suggest that a moderate amount of NO production is essential for fertilization and early embryo development in mice.