Rat sperm AS-A: subcellular localization in testis and epididymis and surface distribution in epididymal sperm

Ligands and Receptors Involved in the Sperm-Zona Pellucida Interactions in Mammals

Sperm-zona pellucida (ZP) interaction, involving the binding of sperm surface ligands to complementary carbohydrates of ZP, is the first direct gamete contact event crucial for subsequent gamete fusion and successful fertilization in mammals. It is a complex process mediated by the coordinated engagement of multiple ZP receptors forming high-molecular-weight (HMW) protein complexes at the acrosomal region of the sperm surface. The present article aims to review the current understanding of sperm-ZP binding in the four most studied mammalian models, i.e., murine, porcine, bovine, and human, and summarizes the candidate ZP receptors with established ZP affinity, including their origins and the mechanisms of ZP binding. Further, it compares and contrasts the ZP structure and carbohydrate composition in the aforementioned model organisms. The comprehensive understanding of sperm-ZP interaction mechanisms is critical for the diagnosis of infertility and thus becomes an integral part of assisted reproductive therapies/technologies.

Reciprocal surface expression of arylsulfatase A and ubiquitin in normal and defective mammalian spermatozoa

Defective mammalian spermatozoa are marked on their surface by proteolytic chaperone ubiquitin. To identify potential ubiquitinated substrates in the defective spermatozoa, we resolved bull sperm protein extracts on a two-dimensional gel and isolated a 64-65-kDa spot (p64) corresponding to one of the major ubiquitin-immunoreactive bands observed in the one-dimensional Western blots. Immune serum raised against this protein recognized a prominent, possibly glycosylated band/spot in the range of 55-68 kDa, consistent with the original spot used for immunization. Internal sequences obtained by Edman degradation of this spot matched the sequence of arylsulfatase A (ARSA), the sperm acrosomal enzyme thought to be important for fertility. By immunofluorescence, a prominent signal was detected on the acrosomal surface (boar and bull) and on the sperm tail principal piece (bull). A second immune serum raised against a synthetic peptide corresponding to an immunogenic internal sequence (GTGKSPRRTL) of the porcine ARSA also labeled sperm acrosome and principal piece. Both sera showed diminished immunoreactivity in the defective bull spermatozoa co-labeled with an anti-ubiquitin antibody. Western blotting and image-based flow cytometry (IBFC) confirmed a reduced ARSA immunoreactivity in the immotile sperm fraction rich in ubiquitinated spermatozoa. Larger than expected ARSA-immunoreactive bands were found in sperm protein extracts immunoprecipitated with anti-ubiquitin antibodies and affinity purified with matrix-bound, recombinant ubiquitin-binding UBA domain. These bands did not show the typical pattern of ARSA glycosylation but overlapped with bands preferentially binding the Lens culinaris agglutinin (LCA) lectin. By both epifluorescence microscopy and IBFC, the LCA binding was increased in the ubiquitinated spermatozoa with diminished ARSA immunoreactivity. ARSA was also found in the epididymal fluid suggesting that in addition to intrinsic ARSA expression in the testis, epididymal spermatozoa take up ARSA on their surface during the epididymal passage. We conclude that sperm surface ARSA is one of the ubiquitinated sperm surface glycoproteins in defective bull spermatozoa. Defective sperm surface thus differs from normal sperm surface by increased ubiquitination, reduced ARSA binding, and altered glycosylation.

Localization of cathepsin D in mouse reproductive tissues and its acquisition onto sperm surface during epididymal sperm maturation

Sperm maturation in the epididymis involves multiple complex events, that include the adsorption of epididymal secretory proteins, re-organization and removal of sperm surface ligands. In this study, we investigated the existence and distribution of cathepsin D (CAT-D) transcripts and proteins in mouse reproductive tissues and proposed a transfer mechanism of CAT-D to the sperm surface. CAT-D transcripts were highly expressed in cultured Sertoli cells, but not in germ cells. The transcriptional level was relatively higher in the caput epididymis (CP) than in the cauda epididymis (CD). At the translational level, CAT-D was detected in testicular somatic cells and in the principal and basal cells in the CP. The expression of CAT-D was fairly specific to the clear cells in the CD. All forms of CAT-D were detected in ultracentrifuged epididymosomes. In conjunction with the expression levels in epididymal epithelium and epididymosomes, CAT-D expression level on the sperm surface was relatively high in CP sperm, but gradually declined toward the CD. Overall, our results indicated that CAT-D was not inherent to sperm themselves, but rather of epididymal origin and was presumably transported to the sperm surface via epididymosomes.

Cell-surface arylsulfatase A and B on sinusoidal endothelial cells, hepatocytes, and Kupffer cells in mammalian livers

Arylsulfatase A (ARSA) and B (ARSB) have been regarded as lysosomal enzymes because of their hydrolytic activity on synthetic aromatic substrates and the lysosomal localization of their enzymatic activity. Using sea urchin embryos, we previously demonstrated that the bulk of ARS is located on the cell surface of the epithelium, colocalizing with sulfated polysaccharides, and that it does not exhibit enzymatic activity. To examine whether ARSA and ARSB exist on the cell surface in mammalian tissues, we raised antibodies against ARSA and ARSB and examined immunohistochemically their localization in the liver using light and electron microscopy. Here we show that mammalian ARSA and ARSB exist on the cell surface of sinusoidal endothelial cells, hepatocytes, and sinusoidal macrophages (Kupffer cells), as well as in the lysosome. They are also colocalized with heparan sulfate proteoglycan. These results suggest that ARSA and ARSB also may function in the cell surface of mammals. This is the first report to show cell-surface localization of ARS in mammalian somatic cells. The extracellular localization of ARS will provide new insight for human ARS deficiency disorders, such as metachromatic leukodystrophy and mucopolysaccharidosis VI.

Changes in the activity of soluble arylsulphatase during the post-hatch development and regression after light reduction of Japanese quail testes and epididymides

This study demonstrates that specific activity of soluble arylsulphatase (AS) during post-hatch development of Japanese quail testes is the highest for testes weighing from 20 to 200mg, and then decreases as the weight of testes increases, while AS activity per g of wet tissue decreases steadily for testes weighing over 20 to 30 mg. Total AS activity showed a steady increase with the increasing weight of testes. The highest increments in the enzyme activity concerned testes weighing up to 30 mg and those weighing from 30 to 150 mg. Mature animals with testes weighing from 2 to 4 g showed an equal level of total AS activity. Based on this data it is suggested that the changes found in the enzyme activity concern mainly arylsulphatase from Sertoli cells. Specific activity of AS in epididymides remains low until testes reach a weight of approximately 1g and then increases, reaching maximal values for epididymides from the testes of sexually mature animals. Testicular and epididymal regression induced by a short photoperiod (6L:18D) after 30 days of the experiment increases AS activity in the testes and reduces its activity in the epididymides to the values found in the early stages of development. Testes and epididymides in the earliest stage of post-hatch development are characterized by an elution profile of AS in which the form of the enzyme bound to the strong anion exchanger at pH 6.0 is predominant, while in mature animals the form of the enzyme unbound to the anion exchanger predominates in the testes and epididymides. After 30-day regression of the testes and epididymides, the form bound to the anion exchanger did not increase, which suggests that the organs do not return exactly to the stage before sexual maturity.