Chemical Characterization of N-Linked Oligosaccharide As the Antigen Epitope Recognized by an Anti-Sperm Auto-Monoclonal Antibody, Ts4

The fluid factor OVGP1 provides a significant oviductal microenvironment for the reproductive process in golden hamster†

The mammalian oviductal lumen is a specialized chamber that provides an environment that strictly regulates fertilization and early embryogenesis, but the regulatory mechanisms to gametes and zygotes are unclear. We evaluated the oviductal regulation of early embryonic development using Ovgp1 (encoding an oviductal humoral factor, OVGP1)-knockout golden hamsters. The experimental results revealed the following: (1) female Ovgp1-knockout hamsters failed to produce litters; (2) in the oviducts of Ovgp1-knockout animals, fertilized eggs were sometimes identified, but their morphology showed abnormal features; (3) the number of implantations in the Ovgp1-knockout females was low; (4) even if implantations occurred, the embryos developed abnormally and eventually died; and (5) Ovgp1-knockout female ovaries transferred to wild-type females resulted in the production of Ovgp1-knockout egg-derived OVGP1-null litters, but the reverse experiment did not. These results suggest that OVGP1-mediated physiological events are crucial for reproductive process in vivo, from fertilization to early embryonic development. This animal model shows that the fate of the zygote is determined not only genetically, but also by the surrounding oviductal microenvironment.

Role of the Glycosylphosphatidylinositol-Anchored Protein TEX101 and Its Related Molecules in Spermatogenesis

Glycosylphosphatidylinositol (GPI)-anchored proteins (APs) on the plasma membrane are involved in several cellular processes, including sperm functions. Thus far, several GPI-APs have been identified in the testicular germ cells, and there is increasing evidence of their biological significance during fertilization. Among GPI-APs identified in the testis, this review focuses on TEX101, a germ cell-specific GPI-AP that belongs to the lymphocyte antigen 6/urokinase-type plasminogen activator receptor superfamily. This molecule was originally identified as a glycoprotein that contained the antigen epitope for a specific monoclonal antibody; it was produced by immunizing female mice with an allogenic testicular homogenate. This review mainly describes the current understanding of the biochemical, morphological, and physiological characteristics of TEX101. Furthermore, future avenues for the investigation of testicular GPI-Aps, including their potential role as regulators of ion channels, are discussed.

NMR and Molecular Recognition of N-Glycans: Remote Modifications of the Saccharide Chain Modulate Binding Features

Glycans play a key role as recognition elements in the communication of cells and other organisms. Thus, the analysis of carbohydrate–protein interactions has gained significant importance. In particular, nuclear magnetic resonance (NMR) techniques are considered powerful tools to detect relevant features in the interaction between sugars and their natural receptors. Here, we present the results obtained in the study on the molecular recognition of different mannose-containing glycans by Pisum sativum agglutinin. NMR experiments supported by Corcema-ST analysis, isothermal titration calorimetry (ITC) experiments, and molecular dynamics (MD) protocols have been successfully applied to unmask important binding features and especially to determine how a remote branching substituent significantly alters the binding mode of the sugar entity. These results highlight the key influence of common structural modifications in natural glycans on molecular recognition processes and underscore their importance for the development of biomedical applications.

Identification of an anti-sperm auto-monoclonal antibody (Ts4)-recognized molecule in the mouse sperm acrosomal region and its inhibitory effect on fertilization in vitro

We previously established an anti-mouse sperm auto-monoclonal antibody, Ts4, which shows immunoreactivity against several kinds of glycoproteins in the acrosomal region of epididymal spermatozoa, testicular germ cells, and early embryo, via binding to an epitope containing a common N-linked oligosaccharide (OS) chain on the molecules. In mice, we have already demonstrated that the OS chain in the epitope for Ts4 is a fucosylated agalacto-complex-type biantennary glycan carrying bisecting N-acetylglucosamine. In the testis, one of the specific OS chain-conjugated molecules is TEX101, a germ cell-marker glycoprotein, which is expressed in spermatocytes, spermatids, and testicular spermatozoa, but not in epididymal spermatozoa. In this study, we identified a Ts4-reactive glycoprotein in mouse cauda epididymal sperm. An immunoprecipitation method together with liquid chromatography-tandem mass spectrometry showed that alpha-N-acetylglucosaminidase (Naglu; a degradation enzyme of heparan sulfate) is one of the glycoproteins recognized by Ts4 in the epididymal spermatozoa. Western blot and immunohistochemical analyses revealed that mouse Naglu exists in two forms (82 and 77kDa) and is expressed in the acrosomal region and the flagellum of cauda epididymal sperm. Of the two Naglu-forms expressed in sperm, Ts4 immunoreacted against only the 82-kDa form located on the acrosomal region. The Ts4 mAb and anti-Naglu pAb negatively affected mouse fertilization in vitro. In addition, Ts4 inhibited sperm acrosome reaction induced by heparan sulfate. The Ts4-recognized fucosylated agalactobiantennary complex-type glycan with bisecting N-acetylglucosamine and Naglu on cauda epididymal spermatozoa may play a role in the process of fertilization.