A glycolytic product is obligatory for initiation of the sperm acrosome reaction and whiplash motility required for fertilization in the mouse

Abstract

The substrate requirements for capacitation of epididymal mouse spermatozoa, initiation of the acrosome reaction and support of fertilization of mouse eggs in vitro were examined by assessing not only fertilization rates, but also the stages of egg activation and sperm head decondensation in fertilized eggs to monitor the temporal aspects of these processes. Although early events of capacitation did not require exogenous substrates, the fertilization process was effectively blocked at the terminal stages of capacitation in the absence of a glycolysable sugar, and addition of glucose was obligatory to initiate both the acrosome reaction and the whiplash motility associated with fertilizing ability. Once the spermatozoa had been primed by glucose, however, the removal of exogenous glucose did not block fertilization. The need for oxidative metabolism was excluded because successful fertilization could be achieved with glucose as the sole exogenous substrate under strictly anaerobic conditions or in the presence of 2.5 μM-oligomycin. We suggest, therefore, that epididymal mouse spermatozoa can be almost completely capacitated in the absence of metabolic processes simply by release into substrate-free medium. They require exposure to glucose to permit induction of the acrosome reaction and motility changes, necessary prerequisites for fertilization; such exposure is followed by rapid and synchronous penetration of eggs.