Spam1 (PH-20) expression in the extratesticular duct and accessory organs of the mouse: a possible role in sperm fluid reabsorption

SPAM1/HYAL5 double deficiency in male mice leads to severe male subfertility caused by a cumulus-oocyte complex penetration defect

The glycosylphosphatidylinositol-anchored sperm hyaluronidases (Hyals), sperm adhesion molecule 1 (SPAM1) and HYAL5, have long been believed to assist in sperm penetration through the cumulus-oocyte complex (COC), but their role in mammalian fertilization remains unclear. Previously, we have shown that mouse sperm devoid of either Spam1 or Hyal5 are still capable of penetrating the COC and that the loss of either Spam1 or Hyal5 alone does not cause male infertility in mice. In the present study, we found that Spam1/Hyal5 double knockout (dKO) mice produced significantly fewer offspring compared with wild-type (WT) mice, and this was due to defective COC dispersal. A comparative analysis between WT and Spam1/Hyal5 dKO epididymal sperm revealed that the absence of these 2 sperm Hyals resulted in a marked accumulation of sperm on the outside of the COC. This impaired sperm activity is likely due to the deficiency in the sperm Hyals, even though other somatic Hyals are expressed normally in the dKO mice. The fertilization ability of the Spam1/Hyal5 dKO sperm was restored by adding purified human sperm Hyal to the in vitro fertilization medium. Our results suggest that Hyal deficiency in sperm may be a significant risk factor for male sterility.-Park, S., Kim, Y.-H., Jeong, P.-S., Park, C., Lee, J.-W., Kim, J.-S., Wee, G., Song, B.-S., Park, B.-J., Kim, S.-H., Sim, B.-W., Kim, S.-U., Triggs-Raine, B., Baba, T., Lee, S.-R., Kim, E. SPAM1/HYAL5 double deficiency in male mice leads to severe male subfertility caused by a cumulus-oocyte complex penetration defect.

Detection of extracellular vesicles in the mouse vaginal fluid: Their delivery of sperm proteins that stimulate capacitation and modulate fertility

Extracellular vesicles (EVs) were isolated by ultracentrifugation of vaginal luminal fluid (VLF) from superovulated mice and identified for the first time using transmission electron microscopy. Characterized by size and biochemical markers (CD9 and HSC70), EVs were shown to be both microvesicular and exosomal and were dubbed as "Vaginosomes" (VGS). Vaginal cross-sections were analyzed to visualize EVs in situ: EVs were present in the lumen and also embedded between squamous epithelial and keratinized cells, consistent with their endogenous origin. Western blots detected Plasma membrane Ca²⁺ -ATPase 1 (PMCA1) and tyrosine-phosphorylated proteins in the VGS cargo and also in uterosomes. Flow cytometry revealed that following coincubation of caudal sperm and VLF for 30 min, the frequencies of cells with the highest Sperm adhesion molecule 1 (SPAM1), PMCA1/4, and PMCA1 levels increased 16.4-, 8.2-, and 27-fold, respectively; compared with control coincubated in phosphate buffered saline (PBS). Under identical conditions, sperm tyrosine-phosphorylated proteins were elevated ~3.3-fold, after VLF coincubation. Progesterone-induced acrosome reaction (AR) rates were significantly (p < 0.001) elevated in sperm coincubated with VGS for 10-30 min, compared with PBS. Sperm artificially deposited in the vaginas of superovulated females for these periods also showed significant (p < 0.01) increases in AR rates, compared with PBS. Thus in vitro and in vivo, sperm acquire from the vaginal environment factors that induce capacitation, explaining recent findings for their acrosomal status in the isthmus. Overall, VGS appear to deliver higher levels of proteins involved in preventing premature capacitation and AR than those promoting them. Our findings which have implications for humans open the possibility of new approaches to infertility treatment with exosome therapeutics.

Junctional adhesion molecule A: expression in the murine epididymal tract and accessory organs and acquisition by maturing sperm

STUDY QUESTION

Is junctional adhesion molecule A (JAM-A), a sperm protein essential for normal motility, expressed in the murine post-testicular pathway and involved in sperm maturation?

SUMMARY ANSWER

JAM-A is present in the prostate and seminal vesicles and in all three regions of the epididymis where it is secreted in epididymosomes in the luminal fluid and can be delivered to sperm in vitro.

WHAT IS KNOWN ALREADY

JAM-A shares with the plasma membrane Ca2+ATPase 4 (PMCA4, the major Ca2+ efflux pump in murine sperm) a common interacting partner, CASK (Ca2+/CaM-dependent serine kinase). JAM-A, like PMCA4, plays a role in Ca2+ regulation, since deletion of Jam-A results in significantly elevated intracellular Ca2+ levels and reduced sperm motility. Recently, PMCA4 was reported to be expressed in the epididymis and along with CASK was shown to be in a complex on epididymosomes where it was transferred to sperm. Because of the association of JAM-A with CASK in sperm and because of the presence of PMCA4 and CASK in the epididymis, the present study was performed to determine whether JAM-A is expressed in the epididymis and delivered to sperm during their maturation.

STUDY DESIGN, SIZE, DURATION

The epididymides, prostate and seminal vesicles were collected from sexually mature C57BL/6J and Institute for Cancer Research mice and antibodies specific for JAM-A and Ser285 -phosphorylated JAM-A (pJAM-A) were used for the analysis. Tissues, sperm and epididymal luminal fluid (ELF) were studied. Epididymosomes were also isolated for study. Caput and caudal sperm were co-incubated with ELF individually to determine their abilities to acquire JAM-A in vitro.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Sections of all three regions of the epididymis were subjected to indirect immunofluorescence analysis. Epididymal tissues, fluid, sperm, prostate and seminal vesicle tissues were analyzed for JAM-A and/or pJAM-A via western blotting analysis. The relative amounts of JAM-A and pJAM-A among epididymal tissues, ELF and sperm were detected by western blot via quantification of band intensities. Epididymosomes were isolated by ultracentrifugation of the ELF after it was clarified to remove cells and tissue fragments, and the proteins western blotted for JAM-A and pJAM-A, and exosomal biochemical markers. FACS analysis was used to quantify the amount of JAM-A present on caput and caudal sperm, as well as the amount of JAM-A acquired in vitro after their co-incubation with ELF.

MAIN RESULTS AND THE ROLE OF CHANCE

Western blots revealed that JAM-A is expressed in all three regions of the epididymis, the prostate and seminal vesicles. As confirmed by indirect immunofluorescence, a western blot showed that JAM-A has a higher expression in the corpus and caudal regions, where it is significantly (P < 0.01) more abundant than in the caput. Both JAM-A and Ser285-phosphorylated JAM-A (pJAM-A) are secreted into the ELF where it is highest in the distal regions. In the ELF, both JAM-A and pJAM-A were detected in epididymosomes. Western blotting of sperm proteins showed a significant (P < 0.01) increase of JAM-A and pJAM-A in caudal, compared with caput, sperm. Flow-cytometric analysis confirmed the increase in JAM-A in caudal sperm where it was 1.4-fold higher than in caput ones. Co-incubation of caput and caudal sperm with ELF demonstrated ~2.3- and ~1.3-fold increases, respectively, in JAM-A levels indicating that epididymosomes transfer more JAM-A to caput sperm that are less saturated with the protein than caudal ones.

LARGE SCALE DATA

Not applicable.

LIMITATIONS, REASONS FOR CAUTION

First, although the ELF was clarified prior to ultracentrifugation for epididymosome isolation, we cannot rule out contamination of the epididymosomal proteins by those from epididymal epithelial cells. Second, the JAM-A detected in the prostate and seminal vesicles might not necessarily be secreted from those organs and may only be present within the tissues, where it would be unable to impact sperm in the ejaculate.

WIDER IMPLICATIONS OF THE FINDINGS

Although performed in the mouse the study has implications for humans, as the highly conserved JAM-A is a signaling protein in human sperm. There is physiological significance to the finding that JAM-A, which regulates sperm motility and intracellular Ca2+, exists in elevated levels in the cauda where sperm gain motility and fertilizing ability. The study suggests that the acquisition of JAM-A in the epididymal tract is involved in the mechanism by which sperm gain their motility during epididymal maturation. This increased understanding of sperm physiology is important for aspects of ART.

STUDY FUNDING AND COMPETING INTEREST(S)

The work was supported by NIH-RO3HD073523 and NIH-5P20RR015588 grants to P.A.M.-D. The authors declare there are no conflicts of interests.

Acrosome markers of human sperm

Molecular biomarkers that can assess sperm acrosome status are very useful for evaluating sperm quality in the field of assisted reproductive technology. In this review, we introduce and discuss the localization and function of acrosomal proteins that have been well studied. Journal databases were searched using keywords, including "human acrosome", "localization", "fertilization-related protein", "acrosomal membrane", "acrosomal matrix", "acrosome reaction", "knockout mouse", and "acrosome marker".

Acidic hyaluronidase activity is present in mouse sperm and is reduced in the absence of SPAM1: evidence for a role for hyaluronidase 3 in mouse and human sperm

The molecular mechanisms underlying sperm penetration of the physical barriers surrounding the oocyte have not been completely delineated. Although neutral-active or "reproductive" hyaluronidases (hyases), exemplified by Sperm Adhesion Molecule 1 (SPAM1), are thought to be responsible for hyaluronan digestion in the egg vestments and for sperm-zona binding, their roles in mouse sperm have been recently questioned. Here we report that acidic "somatic" Hyaluronidase 3 (HYAL3), a homolog of SPAM1 with 74.6% structural similarity, exists in two isoforms in human ( approximately 47 and approximately 55 kDa) and mouse ( approximately 44 and approximately 47 kDa) sperm, where it resides on the plasma membrane over the head and midpiece. Mouse isoforms are differentially distributed in the soluble (SAP), membrane (MBP), and acrosome-reacted (AR) fraction where they are most abundant. Comparisons of zymography of Hyal3 null and wild-type (WT) AR and MBP fractions show significant HYAL3 activity at pH 3 and 4, and less at pH 7. At pH 4, a second acid-active hyase band at approximately 57 kDa is present in the AR fraction. HYAL3 activity was confirmed using immunoprecipitated HYAL3 and spectrophotometry. In total proteins, hyase activity was higher at pH 6 than at 4, where Spam1 nulls had significantly (P < 0.01) diminished activity implicating an acidic optima for murine SPAM1. Although fully fertile, Hyal3 null sperm showed delayed cumulus penetration and reduced acrosomal exocytosis. HYAL3 is expressed in epididymal tissue/fluid, from where it is acquired by caudal mouse sperm in vitro. Our results reveal concerted activity of both neutral- and acid-active hyaluronidases in sperm.

Mammalian hyaluronidase induces ovarian granulosa cell apoptosis and is involved in follicular atresia

During ovarian folliculogenesis, the vast majority of follicles will undergo atresia by apoptosis, allowing a few dominant follicles to mature. Mammalian hyaluronidases comprise a family of six to seven enzymes sharing the same catalytic domain responsible for hyaluronan hydrolysis. Interestingly, some of these enzymes have been shown to induce apoptosis. In the ovary, expression of three hyaluronidases (Hyal-1, Hyal-2, and Hyal-3) has been documented. However, their precise cellular localization and role in ovarian regulation have not yet been defined. We herein investigated the possible involvement of these enzymes in ovarian atresia. First, we established a mouse model for ovarian atresia (gonadotropin withdrawal by anti-equine chorionic gonadotropin treatment) and showed that the mRNA levels of Hyal-1, Hyal-2, and Hyal-3 were significantly increased in apoptotic granulosa cells as well as in atretic follicles. Second, using ovaries of normally cycling mice, we demonstrated the correlation of Hyal-1 mRNA and protein expression with cleavage of caspase-3. In addition, we showed that expression of all three hyaluronidases induced apoptosis in transfected granulosa cells. Significantly, the induction of apoptosis by hyaluronidases was independent of catalytic activity, because enzymatically inactive Hyal-1 mutant (D157A/E159A) was as efficient as the wild-type enzyme in apoptosis induction. The activation of the extrinsic apoptotic signaling pathway was involved in this induction, because increased levels of cleaved caspase-8, caspase-3, and poly-ADP-ribose polymerase (PARP) were observed upon hyaluronidase ectopic expression. Our present findings provide a better understanding of the role of hyaluronidases in ovarian functions, showing for the first time their involvement in follicular atresia.

Preliminary characterization of multiple hyaluronidase forms in boar reproductive tract

Hyaluronidases play an important role in gamete interaction and fertility in mammals. The objectives of the present study were to investigate multiple forms of the enzyme in boar reproductive tract using electrophoretic methods. Two forms of hyaluronidase (EC 3.2.1.35) were detected in boar seminal plasma (relative molecular masses of 55,000 and 65,000) using hyaluronic acid-substrate polyacrylamide gel electrophoresis in the presence of SDS. These two forms can be separated by means of affinity chromatography on Heparin-Sepharose. They differ, besides their affinity to heparin, also in the pH optimum of their enzymatic activity. The form with relative molecular mass of 55,000 was active both at the acidic (pH 3.7) and the neutral pH (pH 7.4) and was bound to immobilized heparin. The second form (relative molecular mass 65,000) was active only at acidic pH and did not interact with heparin. The same acidic-active form (65,000) was found in seminal vesicle fluids. The hyaluronidase form which is active both at the acidic and the neutral pH (51,000) was detected in epididymal fluid. In the detergent extracts of boar sperm, three active forms of the enzyme were found (relative molecular masses 55,000, 70,000 and 80,000). The form of relative molecular mass 55,000 was active in a wide range of pH (pH 3-8). The forms of relative molecular masses 70,000 and 80,000 were active only at neutral pH.

Expression of SPAM1 (PH-20) in the Murine Kidney Is Not Accompanied by Hyaluronidase Activity: Evidence for Potential Roles in Fluid and Water Reabsorption

BACKGROUND

A role for Sperm Adhesion Molecule 1 (SPAM1) hyaluronidase in murine kidney, where Spam1 transcript levels have been reported to be higher in males, has not been clarified.

METHODS

Spam1 RNA and protein were studied using RT-PCR, in situhybridization, Western blotting, immunohistochemistry and hyaluronic acid substrate gel electrophoresis. Urine volume and osmolality were studied in wild-type and Spam1 null mice.

RESULTS

While RT-PCR supported a tendency of higher RNA expression in males, no sex difference for the protein was detectable in the cortex, medulla, and urine. Transcripts were predominantly localized in the proximal tubules and glomeruli, with lower levels in the medulla. Similarly, Western blotting and immunohistochemistry revealed that SPAM1 is more abundant in the cortex. Hyaluronidase activity was absent at neutral and acidic pH: suggesting non-enzymatic role(s) for SPAM1. Wild-type and Spam1 null mice given free access to water showed significantly reduced urine volumes (p < 0.01; n = 12) in the latter. Baseline urine osmolality was similar in both, leading to a significantly (p < 0.05) lower osmolar output in the nulls. After water deprivation (24 h), a significant (p < 0.01) increase in urine osmolality was seen only for wild-type mice.

CONCLUSION

SPAM1 is implicated in fluid reabsorption and urine concentration.

Murine Spam1 mRNA: involvement of AU-rich elements in the 3'UTR and antisense RNA in its tight post-transcriptional regulation in spermatids

Sperm adhesion molecule1 (SPAM1), the best characterized hyaluronidase gene, is abundantly expressed in the testis. We attempted to overexpress mouse Spam1 via transgenesis using either the endogenous promoter in a BAC or a heterologous Protamine1 promoter for a Spam1 cDNA transgene. Although transgene-copy numbers ranged from 2 to 15 and transgenic transcripts were expressed, there was a general failure of overexpression of the RNA and protein in the testis of all seven founders. Also, three transgenic lines showed a modest downregulation or co-suppression of the RNA for Spam1 and Hyal5, present on the BAC. We provide evidence for the potential involvement of two co-ordinating post-transcriptional regulatory processes in the failure of overexpression: abundant endogenous antisense RNA and adenosine-uridine (AU)-rich element-mediated regulation of RNA turnover. We demonstrate that AU-rich elements (AREs) in the 3'UTR of mRNAs, well-known to interact with trans-acting proteins to target the RNA for (in)stability, are present in Spam1 RNA and specifically bind to six testicular cytoplasmic proteins. These AU-binding proteins (AUBPs) were virtually absent from the kidney where transcripts are rare, and were shown to interact with the cytoskeleton, which modulates mRNA turnover. In addition to a role in the RNAi pathway, antisense RNA can also modulate ARE-mediated regulation of mRNA by hybridizing to the AREs and specifically silencing their function. This potentially links the two processes in the regulation of Spam1 expression. We hypothesize that testicular Spam1 RNA is regulated post-transcriptionally by cis-acting ARE(s) in the 3'UTR which recognize AUBPs and which are modulated by antisense transcripts.

Spam1-associated transmission ratio distortion in mice: elucidating the mechanism

BACKGROUND

While transmission ratio distortion, TRD, (a deviation from Mendelian ratio) is extensive in humans and well-documented in mice, the underlying mechanisms are unknown. Our earlier studies on carriers of spontaneous mutations of mouse Sperm Adhesion Molecule 1 (Spam1) suggested that TRD results from biochemically different sperm, due to a lack of transcript sharing through the intercellular cytoplasmic bridges of spermatids. These bridges usually allow transcript sharing among genetically different spermatids which develop into biochemically and functionally equivalent sperm.

OBJECTIVES

The goals of the study were to provide support for the lack of sharing (LOS) hypothesis, using transgene and null carriers of Spam1, and to determine the mechanism of Spam1-associated TRD.

METHODS

Carriers of Spam1-Hyal5 BAC transgenes were mated with wild-type female mice and the progeny analyzed for TRD by PCR genotyping. Sperm from transgene and Spam1 null carriers were analyzed using flow cytometry and immunocytochemistry to detect quantities of Spam1 and/or Hyal5. Transgene-bearing sperm with Spam1 overexpression were detected by fluorescence in situ hybridization. In wild-type animals, EM studies of in situ transcript hybridization of testis sections and Northern analysis of biochemically fractionated testicular RNA were performed to localize Spam1 transcript. Finally, AU-rich motifs identified in the 3' UTR of Spam1 RNA were assayed by UV cross-linking to determine their ability to interact with testicular RNA binding proteins.

RESULTS

The Tg8 line of transgene carriers had a significant (P < 0.001) TRD, due to reduced fertilizing ability of transgene-bearing sperm. These sperm retained large cytoplasmic droplets engorged with overexpressed Spam1 or Hyal5 protein. Caudal sperm from transgene carriers and caput sperm of null carriers showed a bimodal distribution of Spam1, indicating that the sperm in a male were biochemically different with respect to Spam1 quantities. Spam1 RNA was absent from the bridges, associated exclusively with the ER, and was shown to be anchored to the cytoskeleton. This compartmentalization of the transcript, mediated by cytoskeletal binding, occurs via protein interactions with 3' UTR AU-rich sequences that are likely involved in its stabilization.

CONCLUSION

We provide strong support for the LOS hypothesis, and have elucidated the mechanism of Spam1-associated TRD.

Identification of the bull sperm p80 protein as a PH-20 ortholog and its modification during the epididymal transit

We have identified an 80 kDa protein in ejaculated bull spermatozoa (p80) which is found in acrosomal and post-acrosomal areas of the head. It has a hyaluronidase activity and shares homologies with PH-20, a sperm surface glycoprotein involved in sperm-egg interaction. The aim of the present study was to characterize bull sperm p80 protein at the nucleic and amino acid levels to determine whether it is the bovine PH-20 ortholog. The complete nucleotide sequence determined by RT-PCR, 3' and 5' RACE show that bull p80, displays identity with the PH-20 nucleotide and amino acid sequences. Messenger RNA and protein expressions determined by Northern blot and immunohistochemistry revealed that the protein is testicular (expressed in spermatocytes and spermatids). The localization of p80 on spermatozoa, determined by indirect immunofluorescence using a monoclonal antibody, shows the protein in acrosomal and post acrosomal areas of the head with an increase in the signal intensity as sperm progress through the epididymis. Post-translational modifications of the protein were investigated during the epididymal maturation by Western blot on protein extracts from sperm collected in the caput, corpus and cauda portions of bull epididymis. Glycolysation status of sperm p80 protein on proteins from ejaculated and epididymidal sperm was investigated. Result show that the glycosylation status is modified as spermatozoa migrate through the epididymis. Hyaluronidase activity evaluated in protein extracts from spermatozoa of the three different epididymal sections revealed that the activity is higher at pH 7 than 4 and is not affected by epididymal maturation. These data strongly suggest that p80 is the bovine PH-20.