Expression and localization of PMCA4 in rat testis and epididymis

PMCA4 gene expression is regulated by the androgen receptor in the mouse testis during spermatogenesis

The present study aimed to investigate the expression of ATPase Ca⁺⁺ transporting plasma membrane 4 (PMCA4) in mouse testis and to determine its role in spermatogenesis. Reverse transcription-quantitative PCR, western blotting and immunofluorescence were performed to evaluate the expression levels of PMCA4 in mouse testes at various weeks postnatal in wild type mice, and in testes from Sertoli cell-specific androgen receptor knockout and androgen receptor knockout (ARKO) mice. Luciferase assay, androgen receptor (AR) overexpression and AR antagonist experiments were used to confirm that AR regulated the expression of PMCA4. The results demonstrated that PMCA4 was highly expressed in mouse testes at 3–8 weeks postnatal. PMCA4 expression levels in ARKO mouse testes were decreased compared with wild type. In addition, activation of AR by testosterone administration resulted in an increase in the activity of the PMCA4 promoter. Cells transfected with an AR-overexpressing plasmid exhibited increased expression levels of the PMCA4 protein. Finally, the increase in PMCA4 protein levels induced by testosterone was prevented by pre-treatment with the AR antagonist flutamide. The present results confirmed that PMCA4 was upregulated during mouse testis development and that PMCA4 mRNA and protein expression levels were regulated by androgens and AR. The present findings suggest that PMCA4 may be involved in the regulation of spermatogenesis.

Epididymosomes: transfer of fertility-modulating proteins to the sperm surface

A variety of glycosylphosphatidylinositol (GPI)-linked proteins are acquired on spermatozoa from epididymal luminal fluids (ELF) during sperm maturation. These proteins serve roles in immunoprotection and in key steps of fertilization such as capacitation, acrosomal exocytosis and sperm-egg interactions. Their acquisition on sperm cells is mediated both by membrane vesicles (epididymosomes, EP) which were first reported to dock on the sperm surface, and by lipid carriers which facilitate the transfer of proteins associated with the membrane-free fraction of ELF. While the nonvesicular fraction is more efficient, both pathways are dependent on hydrophobic interactions between the GPI-anchor and the external lipid layer of the sperm surface. More recently proteomic and hypothesis-driven studies have shown that EP from several mammals carry transmembrane (TM) proteins, including plasma membrane Ca 2 + -ATPase 4 (PMCA4). Synthesized in the testis, PMCA4 is an essential protein and the major Ca 2 + efflux pump in murine spermatozoa. Delivery of PMCA4 to spermatozoa from bovine and mouse EP during epididymal maturation and in vitro suggests that the docking of EP on the sperm surface precedes fusion, and experimental evidence supports a fusogenic mechanism for TM proteins. Fusion is facilitated by CD9, which generates fusion-competent sites on membranes. On the basis of knowledge of PMCA4's interacting partners a number of TM and membrane-associated proteins have been identified or are predicted to be present, in the epididymosomal cargo deliverable to spermatozoa. These Ca 2 + -dependent proteins, undetected in proteomic studies, play essential roles in sperm motility and fertility, and their detection highlights the usefulness of the hypothesis-driven approach.

Plasma membrane Ca2+-ATPase 4 in murine epididymis: secretion of splice variants in the luminal fluid and a role in sperm maturation

Plasma membrane Ca(2+)-ATPase isoform 4 (PMCA4) is the primary Ca(2+) efflux pump in murine sperm, where it regulates motility. In Pmca4 null sperm, motility loss results in infertility. We have shown that murine sperm PMCA4b interacts with Ca(2+)/CaM-dependent serine kinase (CASK) in regulating Ca(2+) homeostasis and motility. However, recent work indicated that the bovine PMCA4a splice variant (missing in testis) is epididymally expressed, along with 4b, and may be transferred to sperm. Here we show, via conventional and in situ RT-PCR, that both the splice variants of Pmca4 mRNA are expressed in murine testis and throughout the epididymis. Immunofluorescence localized PMCA4a to the apical membrane of the epididymal epithelium, and Western analysis not only confirmed its presence but showed for the first time that PMCA4a and PMCA4b are secreted in the epididymal luminal fluid (ELF), from which epididymosomes containing PMCA4a were isolated. Flow cytometry indicated the presence of PMCA4a on mature caudal sperm where it was increased ~5-fold compared to caput sperm (detected by Western blotting) and ~2-fold after incubation in ELF, revealing in vitro uptake and implicating PMCA4a in epididymal sperm maturation. Coimmunoprecipitation using pan-PMCA4 antibodies, revealed that both variants associate with CASK, suggesting their presence in a complex. Because they have different kinetic properties for Ca(2+) transport and different abilities to bind to CASK, our study suggests a mechanism for combining the functional attributes of both PMCA4 variants, leading to heightened efficiency of the pump in the maintenance of Ca(2+) homeostasis, which is crucial for normal motility and male fertility.

Dephosphorylated NSSR1 is induced by androgen in mouse epididymis and phosphorylated NSSR1 is increased during sperm maturation

NSSR1 (Neural salient serine/arginine rich protein 1, alternatively SRp38) is a newly identified RNA splicing factor and predominantly expressed in neural tissues. Here, by Western blot analysis and immunofluorescent staining, we showed that the expression of dephosphorylated NSSR1 increased significantly during development of the caput epididymis. In adult mice, phosphorylated NSSR1 was mainly expressed in the apical side of epithelial cells, and dephosphorylated NSSR1 in caput epididymis was upregulated in a testosterone dependent manner. In addition, subcellular immunoreactive distribution of NSSR1 varied in different regions of the epididymis. With respect to the sperm, phosphorylated NSSR1 was detected in the mid-piece of the tail as well as the acrosome. Furthermore, NSSR1 was released from the sperm head during the capacitation and acrosome reaction. These findings for the first time provide the evidence for the potential roles of NSSR1 in sperm maturation and fertilization.

Epididymal lithiasis in roosters: in the middle of the way there was a stone

The epididymal region plays an important role in the reproduction of roosters, as it is the site of functions important in the maintenance of fertility, including fluid and calcium reabsorption and sperm surface modifications. About 10 years ago, a reproductive dysfunction characterized by the formation of luminal calcium stones in the epididymal region of roosters was described. This anomaly, known as epididymal lithiasis, is associated with a significant decrease in the fertility of affected roosters. This reproductive anomaly has been observed in multiple countries and is thought to negatively impact the poultry industry; however, the cause of epididymal lithiasis has not been fully determined. Several hypotheses have been proposed to explain the origin of epididymal lithiasis, including the presence of an infectious agent within the epididymal region, an autoimmune response, increased dietary calcium and vitamin D3 intake and the presence of genetic susceptibility factors; however, none of these has been proven to be the primary cause of the calcium stone formation. Nonetheless, considerable evidence suggests that regardless of the primary cause of epididymal lithiasis, this anomaly could result from a hormonal imbalance or a local impairment of calcium homeostasis in the epididymal region. The objectives of this mini-review are to 1) summarize the reproductive alterations observed in animals affected by epididymal lithiasis, 2) discuss the hypotheses proposed to explain the cause of luminal stone formation and 3) provide perspectives for future studies of this reproductive disorder.

Switch of PMCA4 splice variants in bovine epididymis results in altered isoform expression during functional sperm maturation

Ca(2+) and Ca(2+)-dependent signals are essential for sperm maturation and fertilization. In mouse sperm the plasma membrane Ca(2+)-ATPase (PMCA) isoform 4 plays a crucial role in Ca(2+) transport. The two major splice variants of PMCA4 are PMCA4a and PMCA4b. PMCA4a differs from PMCA4b in the mechanism of calmodulin binding and activation. PMCA4a shows a much higher basal activity and is more effective than PMCA4b in returning Ca(2+) to resting levels. Knock-out mice carrying a PMCA4-null mutation are infertile because their sperm cannot achieve a hyperactivated state of motility. As sperm reach functional maturity during their transit through the epididymis, the expression of PMCA4a and 4b was assessed in bull testis and epididymis. Quantitative PCR revealed that PMCA4b is the major splice variant in testis, caput, and corpus epididymidis. In contrast, PMCA4a is the major splice variant in cauda epididymidis, whereas sperm are transcriptionally silent. Immunohistochemical staining using a new antibody against bovine PMCA4a located the PMCA4a to the apical membrane of the epithelium of cauda epididymidis, whereas testis, caput, and corpus epididymidis were negative. Western blotting of testis, epididymis, and sperm isolated from caput and cauda epididymidis showed a much higher level of PMCA4a in cauda epididymidis and sperm from cauda epididymidis compared with testis membranes and sperm from caput epididymidis. These findings suggest that PMCA4a is transferred to bovine sperm membranes in cauda epididymidis. This isoform switch may facilitate a higher calcium turnover in sperm necessary to traverse the female genital tract.

Surfing the wave, cycle, life history, and genes/proteins expressed by testicular germ cells. Part 5: intercellular junctions and contacts between germs cells and Sertoli cells and their regulatory interactions, testicular cholesterol, and genes/proteins associated with more than one germ cell generation

In the testis, cell adhesion and junctional molecules permit specific interactions and intracellular communication between germ and Sertoli cells and apposed Sertoli cells. Among the many adhesion family of proteins, NCAM, nectin and nectin-like, catenins, and cadherens will be discussed, along with gap junctions between germ and Sertoli cells and the many members of the connexin family. The blood-testis barrier separates the haploid spermatids from blood borne elements. In the barrier, the intercellular junctions consist of many proteins such as occludin, tricellulin, and claudins. Changes in the expression of cell adhesion molecules are also an essential part of the mechanism that allows germ cells to move from the basal compartment of the seminiferous tubule to the adluminal compartment thus crossing the blood-testis barrier and well-defined proteins have been shown to assist in this process. Several structural components show interactions between germ cells to Sertoli cells such as the ectoplasmic specialization which are more closely related to Sertoli cells and tubulobulbar complexes that are processes of elongating spermatids embedded into Sertoli cells. Germ cells also modify several Sertoli functions and this also appears to be the case for residual bodies. Cholesterol plays a significant role during spermatogenesis and is essential for germ cell development. Lastly, we list genes/proteins that are expressed not only in any one specific generation of germ cells but across more than one generation.

Extending the knowledge in histochemistry and cell biology

Central to modern Histochemistry and Cell Biology stands the need for visualization of cellular and molecular processes. In the past several years, a variety of techniques has been achieved bridging traditional light microscopy, fluorescence microscopy and electron microscopy with powerful software-based post-processing and computer modeling. Researchers now have various tools available to investigate problems of interest from bird's- up to worm's-eye of view, focusing on tissues, cells, proteins or finally single molecules. Applications of new approaches in combination with well-established traditional techniques of mRNA, DNA or protein analysis have led to enlightening and prudent studies which have paved the way toward a better understanding of not only physiological but also pathological processes in the field of cell biology. This review is intended to summarize articles standing for the progress made in "histo-biochemical" techniques and their manifold applications.

State-of-the-art technologies, current opinions and developments, and novel findings: news from the field of histochemistry and cell biology

Investigations of cell and tissue structure and function using innovative methods and approaches have again yielded numerous exciting findings in recent months and have added important data to current knowledge, inspiring new ideas and hypotheses in various fields of modern life sciences. Topics and contents of comprehensive expert reviews covering different aspects in methodological advances, cell biology, tissue function and morphology, and novel findings reported in original papers are summarized in the present review.