Qualitative and quantitative analysis of protein expression in the caput and cauda regions of the rat epididymis

Background: The aim of this study was to identify the differentially expressed proteins in the sperm isolated from the caput and the cauda region of the rat epididymis. This is the first study on the quantitative nongel-based proteomics to have identified differentially expressed proteins in the cauda epididymal sperm. Material and Methods: This was achieved by isolation of sperm from the caput and the cauda of the rat epididymis followed by the tryptic digestion of the proteins and the resulted peptides were subjected to isobaric tags for relative and absolute quantitation-label and mass spectrometry (MS)/MS analysis. With the help of quantitative proteomics, we have been able to elucidate some of the major proteins involved in the process of sperm maturation. Results: In total, 999 proteins from the spermatozoa of caput and cauda region of the epididymis were identified. We have reported about 10 downregulated proteins and 15 upregulated proteins that have been in the sperm from the cauda region of the epididymis. HongrES1, the membrane of the SERPIN family specifically expressed in the principal cells of the cauda epididymis, have been found to be expressed three-fold higher. Conclusion: This study contributes to the understanding of the importance of different proteins at the different stages of the maturation during the transit of the spermatozoa. The higher and lower expression of different proteins in the epididymal region depicts their roles in priming the spermatozoa for normal fertilizing ability. Thus, the target proteins can be further studied for the possible development of male contraception.