Synchronous modulation of cell surface lectin and its receptor in a homologous cell population: a novel mechanism of cellular regulation.

Testicular immotile sperm undergo maturation during epididymal transit when these cells pass through caput, corpus, and cauda-epididymal regions. Maturing goat spermatozoa specifically at the distal corpus epididymal stage show head-to-head autoagglutination when incubated in vitro in a modified Ringer's solution. Here, we show the biochemical mechanism of autoagglutination event and its functional significance. A lectin-like molecule located on sperm surface specifically interacts with its receptor of the neighboring homologous cells to cause autoagglutination. Lectin is a Ca++-dependent galactose-specific protein. Failure of the pre- and post-distal corpus sperm to show autoagglutination is due to lack of lectin-like molecule and its receptors, respectively. Maturing sperm at distal corpus stage acquire lectin-like molecule followed by sharp disappearance of its receptor, and this event is synchronously associated with the initiation of sperm forward motility that is essential for fertilization in vivo. Lectin and its receptor isolated from sperm plasma membrane showed high efficacy for blocking autoagglutination phenomenon. The data are consistent with the view that synchronous modulation of homologous cell surface lectin and their receptors constitutes a novel mechanism for cellular regulation by generating waves of signals by manipulating lectin-sugar-dependent "self-talk" and cell-cell "cross-talk".