HYAL2 is a germ cell hyaluronidase : its role in murine sperm function
Date
2012
Authors
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Journal ISSN
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Publisher
University of Delaware
Abstract
Hyaluronidases are enzymes which breakdown hyaluronan (HA) in the extracellular matrix. Five of the six mammalian hyaluronidases (hyases) are expressed in the testis. One of these hyases, the 57 kDa HYAL2 (Hyaluronidase 2), has been highly characterized to be acid-active in somatic tissues, but its expression in sperm has never been studied. This investigation was aimed at determining if HYAL2 is present in sperm and, if so, characterizing its role in sperm function. Immunocytochemistry revealed the presence of HYAL2 on the sperm plasma membrane over the acrosome as well as the midpiece and proximal principal piece of the flagellum. Its presence was confirmed by Western blot analysis which showed relatively high levels of HYAL2 on the inner acrosomal membrane and the soluble acrosomal fraction where acid-active hyases are known to function, and to a lesser extent on the plasma membrane where neutral hyases play a role in cumulus penetration. Western blot analysis also showed HYAL2 to be present throughout the epididymis as well as in the epididymal luminal fluid. In vitro uptake assays demonstrated that HYAL2 can be acquired on the plasma membrane of sperm from epididymal luminal fluid. A zona pellucida-binding assay demonstrated that HYAL2 does not play a major role in sperm-zona binding. While hyaluronic acid substrate gel electrophoresis (HASGE) at both pH 4.0 and 3.0 had earlier shown a 57 kDa sperm hyase to be present in sperm, immunoprecipitated HYAL2 showed no hyase activity at pH 4.0 or 7.0. It is proposed that HYAL2 in mouse sperm works in conjunction with other proteins in performing its catalytic activity in sperm, as it does in somatic tissues. Further, it is proposed to have a unique role in sperm in catabolizing megadalton HA to its 20 kDa intermediate which is a substrate for the neutral hyases, known to be present in sper m, to complete the degradation of HA. None of the other hyases in sperm, unlike somatic tissues where HYAL1 exists, has this ability which is necessary for the catabolism of hyaluronan
during fertilization.