Mouse sperm capacitation assessed by kinetics and morphology of fertilization in vitro

Publisher Website
Google Scholar
Abstract
Epididymal mouse spermatozoa were preincubated for periods of 5-120 min and then tested for their ability to penetrate freshly ovulated eggs synchronously and rapdily. When zona-intact eggs were used, only suspensions preincubated for 120 min gave consistently high rates of fertilization, but suspensions preincubated for 30 min were functionally equivalent to those incubated for 120 min when used with zona-free eggs; the only major observable differences were a 15 min lag in sperm-egg interaction and an increased incidence of asynchrony with multiple sperm [polyspermy] penetrations. A morphological study of sperm-egg interactions using zona-intact eggs indicated that, within 35 min of gamete mixing, egg microvilli could be detected by SEM [scanning electron microscopy] in association with the fertilizing sperm head. Using conventional light microscopic examination of fixed and stained preparations, initial stages of sperm head decondensation could be detected in the majority of eggs after 45-60 min and the process was essentially completed, with the egg at the telophase-2nd polar body stage of meiosis II, after 75 min. Similar kinetics were observed with sperm concentrations of 105 and 106/ml. The time required for penetration by capacitated sperm suspensions is therefore relatively short and the most accurate information regarding state of capacitation and rate of sperm penetration can be obtained by choosing and appropriately short interval for sperm-egg interaction before assessment.