Abstract
BackgroundSperm binding proteins and their C-terminal peptides of the Sperm Associated Antigen 11 (SPAG11) family were found to play an important role in epididymal innate immunity in addition to their role in sperm maturation. However, the expression of Spag11 transcripts in rodents is not well documented.MethodsComputational analysis was employed to identify novel Spag11 isoforms in the rat. RT-PCR analyses were carried out on RNAs isolated from the male reproductive tract tissues of rat using gene specific primers for Spag11c and Spag11t. The identities of PCR products were confirmed by sequencing. Tissue distribution, developmental expression and androgen regulation of Spag11t and Spag11c were studied using RT-PCR. The antimicrobial activities of recombinant Spag11t and Spag11c were tested against E coli in a colony forming unit assay.ResultsIn this study, we identified two novel Spag11 transcripts, namely, Spag11t and Spag11c derived from the long arm of chromosome 16 in the rat (Rattus norvegicus), using both in silico and molecular biology approaches. Spag11c is expressed in all three regions of the epididymis, in testis and in ovary but is absent from the seminal vesicle. Spag11t expression is confined to the caput and it is not expressed in the testis, seminal vesicle or ovary. Age dependent expression of Spag11t and Spag11c was observed in the epididymides of rats (10–60 day old). Their expression was found to be most abundant in the adult rat (60 day) suggesting roles in mature reproductive function. Further, both Spag11t and Spag11c expression was down regulated in castrated rat epididymides and the expression was maintained in the testosterone replaced castrated rats. SPAG11C is a potent antibacterial agent. SPAG11T also displayed bactericidal capacity although weaker than SPAG11C and SPAG11E.ConclusionThe abundant expression of Spag11t and Spag11c in the male reproductive tract suggests an important role in male reproductive tract immunity. Their expression is developmentally regulated and androgen dependent. Characterization of novel SPAG11 isoforms will contribute to our understanding of the role of epididymal proteins in sperm maturation and innate immunity.
Highlights
Spermatozoa leaving the testis are immature and lack fertilizing ability
Two copies of the Spag11 A component encoding Spag11c were discovered in a β-defensin-rich region of rat chromosome 16q12.5 using a homology search strategy
The distant Spag11 A component is located within a genomic segment that includes a copy of ab initio gene model hmm24586 and is at least 250 kb long
Summary
Spermatozoa leaving the testis are immature and lack fertilizing ability During their passage through the epididymis, which provides the environment for sperm maturation and storage, the spermatozoa acquire fertilizing ability and forward motility after interacting with proteins secreted by the epididymal epithelial cells. These secreted proteins are thought to be involved in a range of general and specific reproductive activities including the initiation of sperm maturation [1], sperm-oocyte recognition [2] and the acrosome reaction [3]. The expression of Spag transcripts in rodents is not well documented
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