Calmodulin localization in mammalian spermatozoa.

The location of calmodulin in rabbit and guinea pig spermatozoa was determined by indirect immunofluorescence techniques. Spermatozoa that had not undergone the acrosome reaction exhibited four distinct regions of calmodulin-specific immunofluorescence: around the acrosome, in a band across the lower third of the head, and in two localized areas at the base and tip of the flagellum. In contrast, after the acrosome reaction, although other features of calmodulin distribution remained the same, the fluorescence associated with the anterior half of the head was notably absent. Instead, fluorescence was associated with the membranes that had separated from the sperm head. These findings suggest a potential role for calmodulin in the Ca2+-dependent control of sperm activation, in sperm-egg fusion, and in microtubule disassembly processes in the flagellum.