Alteration of goat sperm ecto-phosphoprotein phosphatase activity and its distribution on the sperm surface during epididymal maturation

Receptor expression is essential for forward motility in the course of sperm cell maturation

Forward motility stimulating factor (FMSF) is a glycoprotein previously purified from buffalo blood serum that promotes progressive motility of caprine caudal spermatozoa. We have prepared a functionally active covalent conjugate of this factor with horseradish-peroxidase (HRP) to obtain an idea of its binding efficacy on maturing spermatozoa. Receptor-assay was performed using FMSF-HRP conjugate in saturating conditions to bind with spermatozoa isolated from different epididymal segments. Activity and binding profile of the motility stimulating factor coincided, suggesting both these parameters come into play only partially when spermatozoa reach the maturation state in the distal-corpus region and largely in caudal part (around 24% and 80% binding and 10% and 79% forward motility, respectively). Spermatozoa from caput up to mid-corpus regions neither displayed any substantial binding with FMSF nor exhibited significant induction in forward motility. Study of cell surface-bound FMSF on maturing spermatozoa in physiological milieu demonstrated their presence on anterior spermhead and suggests a nearly similar pattern of occurrence. Flow-cytometric analysis also implies analogous presence of this receptor. The factor was also immunodetected in uterine fluids of cattle species. This study displays a maturation-dependent expression of FMSF-receptor and consequential stimulation of forward motility that may be crucial for its journey to meet the ovum.

Experimental varicocoele in rats affects mechanisms that control expression and function of the androgen receptor

Varicocoele is an important cause of male infertility. Normal male reproductive function and fertility depends on a delicate balance between androgen receptor (AR) and the classic oestrogen receptors ESR1 (ERα) and ESR2 (ERβ). Using a model of surgically induced varicocoele in rats, this study aimed to investigate the effects of varicocoele on the expression of AR, ESR1, ESR2 and G-protein coupled oestrogen receptor (GPER). Varicocoele did not affect the mRNA and protein expression of ESR1 and ESR2 in both testes. Varicocoele did not affect the mRNA and protein expression of GPER in the right testis, but slightly reduced the mRNA and increased the protein levels in the left testis. Varicocoele did not affect the mRNA for AR, but reduced the protein levels in both testes. A proteomic approach was used in an attempt to find differentially expressed targets with possible correlation with AR downregulation. Varicocoele caused the differential expression of 29 proteins. Six proteins were upregulated, including the receptor for activated C kinase 1 (RACK1), and 23 were downregulated, including dihydrolipoamide dehydrogenase, alpha-enolase and pyrophosphatase 1. Western blot analysis confirmed that varicocoele upregulated the expression of RACK1, a protein involved with tyrosine phosphorylation and regulation of AR transcriptional activity, AR metabolism and dynamics of the blood-testis barrier. In conclusion, this study suggests that varicocoele affects mechanisms that control AR expression and function. This regulation of AR may play an important role in the varicocoele-induced testicular dysfunction. Furthermore, varicocoele downregulates several other proteins in the testis that may be useful markers of spermatozoa function and male infertility.

A novel membrane protein-specific serine/threonine kinase: tissue distribution and role in sperm maturation

Our recent studies have described for the first time the purification of an ectoprotein kinase to apparent homogeneity using caprine sperm as the model. Purified ectokinase (CIK) is a novel membrane protein-specific kinase that phosphorylates serine and threonine residues of ectophosphoproteins. This study, using ELISA based on ecto-CIK antibody demonstrates that ecto-CIK level is remarkably higher in the sperm membrane than in the cytosol. The epididymal sperm maturational event as well as sperm vertical velocity is associated with a significant increase in the ecto-CIK level. Ecto-CIK, the membrane protein-specific kinase, is also present in all the tissues tested and is predominantly localized in the cell membrane. Ubiquitous localization of the novel kinase on the mammalian cell membrane suggests that the kinase may play pivotal role in gamete as well as somatic cell regulation by modulating membrane biology through serine/threonine phosphorylation of specific membrane proteins located in the ectodomains.

Cell surface phosphorylation by a novel ecto-protein kinase: a key regulator of cellular functions in spermatozoa

Since 1976 many studies have been reported on the occurrence and functional significance of ecto-protein kinases in a variety of cell types although their precise biochemical identity is largely unknown. This study reports for the first time purification to apparent homogeneity of an ecto-protein kinase (ecto-CIK) and some of its characteristics using caprine sperm as the cell model. The ecto-CIK is a unique membrane-specific serine/threonine protein kinase. It is a strongly basic 115 kDa protein made up of two subunits: 63 and 55 kDa. The ecto-kinase undergoes a remarkable lateral movement on the outer cell surface culminating in capping on the sperm acrosomal tip. MPS, its major protein substrate is also located on the acrosomal tip. Both ecto CIK and MPS serve as potential regulators of flagellar motility. This novel enzyme appears to be major kinase responsible for the reported regulation of mammalian cellular functions by modulating phosphorylation of the membrane-bound proteins.

Isolation and biochemical characteristics of a molecular form of epididymal acid phosphatase of boar seminal plasma

The fluid of boar epididymis is characterized by a high activity of acid phosphatase (AcP), which occurs in three molecular forms. An efficient procedure was developed for the purification of a molecular form of epididymal acid phosphatase from boar seminal plasma. We focused on the epididymal molecular form, which displayed the highest electrophoretic mobility. The purification procedure (dialysis, ion exchange chromatography, affinity chromatography and hydroxyapatite chromatography) used in this study gave more than 7000-fold purification of the enzyme with a yield of 50%. The purified enzyme was homogeneous by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE). The purified molecular form of the enzyme is a thermostable 50kDa glycoprotein, with a pI value of 7.1 and was highly resistant to inhibitors of acid phosphatase when p-nitrophenyl phosphate was used as the substrate. Hydrolysis of p-nitrophenyl phosphate by the purified enzyme was maximally active at pH of 4.3; however, high catalytic activity of the enzyme was within the pH range of 3.5-7.0. Kinetic analysis revealed that the purified enzyme exhibited affinity for phosphotyrosine (K(m)=2.1x10(-3)M) and was inhibited, to some extent, by sodium orthovanadate, a phosphotyrosine phosphatase inhibitor. The N-terminal amino acid sequence of boar epididymal acid phosphatase is ELRFVTLVFR, which showed 90% homology with the sequence of human, mouse or rat prostatic acid phosphatase. The purification procedure described allows the identification of the specific biochemical properties of a molecular form of epididymal acid phosphatase, which plays an important role in the boar epididymis.

Identification and characterization of a sperm motility promoting glycoprotein from buffalo blood serum

Early investigators reported the occurrence of unidentified protein factors in biological fluids that may regulate sperm motility essential for fertility potential. This study reports for the first time purification of a forward motility stimulating protein (FMSF-I), to apparent homogeneity, from a biological fluid (buffalo blood serum) and its characterization. FMSF-I is the major motility protein of buffalo serum: a rich source of the factor. FMSF showed high protein specificity and affinity for activating forward motility of goat cauda epididymal spermatozoa. The motility promoter at 0.5 microM level showed maximal activity when nearly 60%-70% of spermatozoa expressed forward motility. It is a 66 kDa monomeric acidic protein rich in aspartate, glutamate, and leucine with isoelectric point of 3.7. FMSF: a Mg2+ -dependent protein binds to concanavalin A-agarose and the glycoprotein nature of FMSF has been confirmed by PAS staining. The factor lost activity completely when treated with alpha-mannosidase showing that the sugar part of the protein is essential for its biological activity. FMSF has no species specificity for its motility-activating potential. Sperm surface has specific receptors of FMSF, which is strongly immunogenic. The factor is present in testis and epididymis although liver is its richest source. Motility promoting efficacy of FMSF is markedly higher than the well-known non-protein motility activators: theophylline and bicarbonate or their combination. FMSF is a physiological activator of sperm motility and as a slaughterhouse byproduct it has potentiality for solving some of the problems of animal breeding, conservation of endangered species, and human infertility: a global social problem.