Novel Aspects of the Sperm-Associated Antigen 11 (SPAG11) Gene Organization and Expression in Cattle (Bos taurus)1

Abstract

Beta-defensins are small cationic peptides exhibiting broad spectrum antimicrobial properties. In humans, many beta-defensin genes are located within a cluster on chromosome 8p23. The sperm associated antigen 11 (SPAG11) gene is contained in this cluster and is unusual among the human beta-defensins due to its complex genomic structure and mRNA splicing pattern. Here we report the genomic organization of the Bos taurus SPAG11 gene located on chromosome 27q1.2, within a cluster of beta-defensin genes. The exon structures of the fused bovine SPAG11 gene and of the mosaic transcripts initiated at both A and B promoters were established, including identification of novel exons and transcripts not previously found in primate or rodent. Evolutionary analysis against primate, rodent, canine, and porcine orthologs was performed. In adult bulls SPAG11C, SPAG11E, and SPAG11U mRNAs were detected predominantly in the male reproductive tract, while SPAG11D transcript was detected in reproductive and nonreproductive tissues and SPAG11V and SPAG11W mRNAs were confined to testis. Differential expression of all six transcripts was observed in tissues from fetal and adult bulls, suggesting that similar mRNA splicing mechanisms govern SPAG11 gene expression during pre- and postnatal development. Immunolocalization of SPAG11C and SPAG11D/E was demonstrated in the epithelium of the epididymis and testis, and SPAG11D in association with epididymal spermatozoa. Recombinant full-length SPAG11D protein was strongly antibacterial, while the SPAG11E C-terminal peptide that contains the beta-defensin motif in its structure was somewhat less potent. Taken together, the results suggest that SPAG11 isoforms perform both immune and reproductive functions in cattle.

Expression of Avian β-Defensin 3, an Antimicrobial Peptide, by Sperm in the Male Reproductive Organs and Oviduct in Chickens: An Immunohistochemical Study

“…In human testes, immunoreactive β-defensin-1 was localized in the Leydig cells and early and elongated spermatids, whereas discrete immunolabeling occurred in pachytene spermatids (Com et al, 2003). Sperm associated antigen II (SPAG II), the gene of which is included in the β-defensin cluster, was immunolocalized in late stage spermatids and in Sertoli cells in cattle testes (Avellar et al, 2007). Therefore, it is suggested that late stage of spermatids produce AvBD-3 in the chicken testes as some of the mammalian spermatids.…”

“…These defensins may play roles not only in innate immunity but also in male fertility, sperm survival in male reproductive tract, and sperm-egg interaction in mammals (Com et al, 2003;Palladino et al, 2003;Yudin et al, 2003;Zhou et al, 2004). Sperm associated antigen (SPAG11), known as epididymal protein 2 (EP2) in monkey, human epididymis 2 (HE2), and rat spag 11, are antimicrobial peptides attached on the sperm surface (Hamil et al, 2000;Yenugu et al, 2004Yenugu et al, , 2006aAvellar et al, 2007). It has not been reported whether avian sperm express antimicrobial peptides.…”

Novel Partners of SPAG11B Isoform D in the Human Male Reproductive Tract1

“…The conserved R 60 [1,5] site of cleavage by TPSAB1 and prohormone convertase suggests an important function. Cleavage at R 60 was suggested to activate SPAG11B/D [48,49] similar to the tightly regulated cleavage activation of alphadefensin human defensin 5 [54] and other defensins [55].…”

“…Human spermatozoa were fixed and stained as previously described [5]. Surplus swim-up spermatozoa were obtained after approval by the University of North Carolina at Chapel Hill Human Subjects Committee and with informed consent and were provided by the Assisted Reproductive Technology Clinic, University of North Carolina at Chapel Hill.…”

“…Their exons are 97%-100% identical. Alternative splicing generates mRNAs encoding more than 20 SPAG11 protein isoforms, designated A through W [3][4][5]. The C-terminal domain (G 72 -I 133 ) of human SPAG11B isoform D (designated SPAG11B/D), containing an antibacterial cationic defensin-like six-cysteine array highly similar to that of human beta-defensin 4 (DEFB4) (previously known as human beta-defensin 2 [hBD2] [6]), places SPAG11B/D in the beta-defensin protein family.…”