Partial characterization of an intra-acrosomal protein, human acrin1 (MN7).

Acrin1 (MN7), a 90-kd glycoprotein, is localized in the sperm acrosome of several rodents. The purpose of this study was to determine the molecular size and subcellular localization of acrin1 (MN7) in human sperm, and its organization in spermatids during spermiogenesis. Immunocytochemical and biochemical analyses revealed that acrin1 (MN7) is localized in the anterior acrosome and its molecular size is 90 kd, the same as in rodents. Based on molecular size, acrin1 (MN7) is likely to be a novel human acrosomal protein. During spermiogenesis, acrin1 (MN7) is initially localized in the head-cap portion of spermatids from the cap phase to the end of the acrosomal phase, and then relocates from the posterior to the anterior region of the acrosome in the maturation phase in spermatids. Such a morphological organization mechanism is also basically the same as that in rodents. Thus, acrin1 (MN7) is a common acrosomal protein of 90 kd in rodents and humans.