This paper reports a new member of the Ly-6/urokinase-type plasminogen activator receptor (uPAR) superfamily of receptors, SAMP14, which is retained on the inner acrosomal membrane of the human spermatozoan following the acrosome reaction; it may have a role in fertilization.
The hamster egg penetration assay performed in the study showed that antibody against SAMP14 significantly inhibited both the binding and fusion of sperm with zona free hamster eggs, which suggests that SAMP14 may have role in one or more events leading to fertilization. It is well known that the equatorial region of the sperm contacts the vitelline membrane prior to sperm internalization. Further, following the acrosome reaction, the inner acrosomal membrane is known to come directly in contact with the egg, leading to the later events of egg penetration. Considering that the concentrations of SAMP14 were highest in the posterior acrosome close to the equatorial region and that it is retained and localized in the inner acrosomal membrane, it is not surprising that the antibody to SAMP14 inhibited both sperm-egg binding and fusion. Recently, another acrosomal membrane protein SAMP32 also localized to the inner acrosomal membrane of the principal piece and equatorial segments. Further, anti-SAMP32 blocked the penetration of zona free hamster eggs by human sperm. The authors conclude that SAMP14 merits further evaluation as a GPI-linked receptor that is retained on the inner acrosomal membrane after acrosomal exocytosis. 8 figures and 44 references