Sperm-associated antigen 11A is expressed exclusively in the principal cells of the mouse caput epididymis in an androgen-dependent manner

Abstract

BackgroundEpididymal sperm maturation occurs via interactions between sperm and proteins secreted by the epididymal epithelium. Although this is an important process, the genes that encode the involved proteins remain largely uncharacterized. Previous studies have demonstrated that the genes involved in sperm maturation are regulated by androgen. Spag11a is an epididymal gene that is influenced by androgen. However, little is known about the putative role of this gene in the sperm maturation process. The objective of this study was to characterize Spag11a in the mouse epididymis.MethodsIn silico analyses were performed to predict signal peptides and functional domains. Spag11a expression was measured by quantitative real-time RT-PCR. Western blots and immunocytochemistry were performed to determine protein expression.ResultsSPAG11A is a member of the beta defensin protein family and constitutes a secretory protein. Spag11a was expressed exclusively in the epididymis. Moreover, it exhibited region-specific expression in the caput, which is typical for genes that are involved in creating a suitable microenvironment for sperm maturation. Mouse Spag11a was regulated by androgen. A significant decrease of Spag11a expression was observed at third day following a gonadectomy (P < 0.001). Interestingly, testosterone replacement therapy was able to maintain the expression almost at the normal level, indicating a dependency on androgen. Besides androgen, testicular factors influenced Spag11a expression in a different way. This was revealed by efferent duct ligation in which Spag11a was transiently up-regulated at the third day following the ligation before returning to the normal level at day 5. Spag11a regional expression was also observed at protein level detected by western immunoblotting which revealed a clear band in the caput but not in other regions. The prediction that SPAG11A is a secretory protein was confirmed by immunocytochemical analyses indicating cell-specific expression mainly in the caput principal cells and detection of the protein in epididymal luminal fluid and spermatozoa.ConclusionsBased on the characteristics of Spag11a, it is likely that this gene has a specific role in epididymal sperm maturation. Further studies using functional assays are necessary to confirm this finding.

Major protein alterations in spermatozoa from infertile men with unilateral varicocele

“… [ 61 ] P61916 NPC2 Epididymal secretory protein E1 precursor ↑ Plays important role in exit of cholesterol from endosomal/ lysosomal compartment. [ 62 , 63 ] P78540 ARG2 Arginase-2, mitochondrial precursor Unilateral varicocele group only Arginase activity negatively associated to sperm concentration and positively with sperm motility. [ 64 - 66 ] Q13733 ATP1A4 Sodium/potassium-transporting ATPase subunit alpha-4 isoform 1 ↓ Essential for germ cell gene expression; sperm with deficiency show bent in the tail, abnormal ion regulation and reduced motility.…”

“…Patients with varicocele are at a disadvantage as the absence of NME 5 signifies the lack of protection from apoptosis and the increase in antioxidants levels [ 61 ], which will contribute to oxidative stress and poor sperm parameters in varicocele patients. NPC precursor is an intracellular cholesterol transporter that acts in concert with Niemann-Pick disease, type C (NPC2) and plays an important role in the exit of cholesterol from the endosomal/lysosomal compartment [ 62 , 63 ]. Our data indicates that NPC2 was overexpressed with medium abundance in the unilateral varicocele group suggesting alterations in membrane fluidity, capacitation and acrosome reaction in these patients.…”

The epididymal amyloid matrix: structure and putative functions

“…This is supported by the fact that cystatins and the well‐established cathelicidin family of AMPs are both cysteine protease inhibitors and based on structure belongs to the same superfamily (Zhu, ). In addition to cystatins and cathelicidin hCAP‐18, the epididymal lumen is particularly rich in other AMPs including over 40 β‐defensins and HE2/SPAG11 (Malm et al ., ; Patil et al ., ; Hall et al ., ; Pujianto et al ., ). It is possible these AMPs may also be a part of the amyloid matrix.…”

β-defensins and the epididymis: contrasting influences of prenatal, postnatal, and adult scenarios

“… 22 35 44 45 46 47 In different species, the epididymis from castrated animals presents down-regulation of different β-defensin transcripts that is reversed in tissues from testosterone-treated castrated animals, suggesting their positive androgen regulation. 16 22 35 38 45 46 47 48 49 50 51 More recently, we discovered a down-regulation in the β-defensin Spag11c mRNA levels in the caput, but not in the cauda epididymidis from castrated adult rats, demonstrating that influence of androgens on β-defensin expression is dependent on the epididymal region analyzed. 44 In addition, mouse Spag11a ( Bin1b ) 50 and Spag11c mRNA levels 44 were not fully maintained at normal levels in the caput epididymidis from testosterone-treated castrated rats, suggesting that their expression is not only dependent on androgens, but also on luminal testicular factors.…”