Epididymal maturation – a crucial step in the post-testicular sperm development

Mammalian spermatozoa after their development in testis undergo the post-testicular maturation in epididymis where acquire their fertilization ability and competence of movement. The epididymis is tissue with very active fluid-absorbing and fluid-secreting activity. Epididymal fluid contains ions and small molecules, proteins, glycoproteins and enzymes. The surface of spermatozoa is exposed directly to the epididymal fluid, and the sperm plasma membrane is significantly changed. Some testicular proteins are altered, masked, or replaced by new proteins/glycoproteins of epididymal origin. Several proteins produced by epididymis have been described in various mammalian species and shown to be associated with spermatozoa suggesting a role in the sperm maturation and/or sperm-egg binding and fusion. We isolated proteins from fluid, tissue and sperm of boar epididymis, and separated them by chromatographic and electrophoretic methods. We searched for known proteins using panel of antibodies and tested proteins of epididymal fluid for binding abilities. In the epididymis, we found proteins described as proteins of seminal plasma and associated with the sperm surface, such as spermadhesins, beta-microseminoprotein and acrosin inhibitor. These proteins were detected in epididymal sperm, fluid and tissue. We showed that some epididymal proteins may bind the spermatozoa and change the binding sites on the sperm surface. We determined and identified some proteins from boar epididymal fluid with affinity to heparin, hyaluronan and zona pellucida glycoproteins. These phenomena indicate that epididymal fluid proteins bind to the sperm surface during epididymal maturation and might subsequently play role in the sperm capacitation or sperm-zona pellucida binding