Identification of differentially expressed proteins between bull X and Y spermatozoa.

Differential expression of genes leads to variation in phenotypes of X and Y sperm, even though some differential gene products are shared through an intercellular bridge. Differentially expressed proteins between X and Y sperm sorted from semen of nine bulls were compared using two-dimensional electrophoresis (2-DE) coupled with mass spectrometry (MS) analysis. Overall, 663±12 and 647±22 protein spots were detected in X sperm and Y sperm, respectively, and 42 significant protein spots were differentially expressed between them (P<0.05). Sixteen of these protein spots were successfully identified by MS and tandem MS and were found to be closely relevant to energy metabolism, stress resistance, cytoskeletal structure and the activity of serine proteases. Expression levels of two of these proteins, CAPZB and UQCRC1, were verified by Western blot. We propose that these differentially expressed proteins may affect the phenotype of X and Y sperm, binding and fusion of sperm/oocyte and development of the zygotic embryo. Our preliminary results provide an overview of differential expression in total protein levels between X and Y spermatozoa. Identification of these altered proteins may provide a theoretical basis for understanding the biological differences between the two types of sperm.