However, the role of other three mouse c-lysozymes in the reproductive tract is not yet clear. Unlike the human and mouse counter parts, the rat Lyzl genes are not characterized. In the rat genome available at GenBank, of the four c-type lysozymes, Lyzl4 sequence is predicted, whereas the other three were annotated using the whole genome shot gun analyses. Except for their gene identification, the functional role is not reported till now. Absence of Lyzl transcripts in the epididymides obtained from 20–60 day old rats, suggests that their expression pattern is not androgen MK-1775 dependent in this organ system. Testicular androgen variation during development in the rat was reported to be significantly different from the epididymis. A steady increase in testosterone levels occurs in the rete testis of 30-130 day old rats. In this study, the presence of Lyzl1, 3 and 6 mRNA transcripts was observed in the testes starting from 30 day post natal development, whereas Lyzl4 was expressed in all the age groups, though minimally during 10-30 days. The expression pattern of Lyzl transcripts analysed in this study seem to correlate with the minimal androgen levels from day 20 to day 40 and increased androgen in the adult, suggesting that Lyzl expression may be androgen dependent during development in the testis. Androgen dependent expression of Lyzl4 during development was reported in the mouse. Further studies are required to determine the molecular mechanisms that operate in controlling the expression of Lyzl transcripts during development. To demonstrate whether Lyzl4 mRNA expression correlates with the protein expression, immunohistochemistry was performed on testicular sections. LYZL4 protein expression in the testes was observed in the germinal epithelium and on the maturing spermatozoa. It is possible that LYZL4 secreted into the lumen could bind to the sperm and aid in their development. Region specific gene expression of a wide variety of testicular and epididymal proteins on the sperm are reported. The presence of LYZL4 specifically on the sperm tail suggests that it is involved in contributing to sperm motility. However, it is intriguing to note that though it is not expressed in the epididymis it is localized on the sperm tail. It is possible that LYZL4 is added on to the surface in the testis and this protein may continue to be present in the tail region in the epididymis. The catalytic mechanism of c-type lysozymes involves the interaction of Glu-35 and Asp-52 of the active site with beta-1,4 glycosidic bond of the substrate. In this study, rat LYZL4 did not exhibit any muramidase and isopeptidase activity at the concentrations tested. This could be due to the replacement of aspartate by glycine in the catalytic site. Such loss of activity due to “changed” amino acids was reported for human SLLP1 and mouse LYZL4 Epididymal proteins secreted into the lumen play a key role in sperm maturation.