Physiological sperm modifications prior to fertilization

KRAPF, D.; VISCONTI, P.; ARRANZ, SILVIA EDA; CABADA, M.

Rosario

Congreso; XLII Reunión anual SAIB; 2006

Mammalian sperm acquire fertilizing capacity after residing in the female tract, where physiological changes named capacitation take place. In animals with external fertilization as amphibians, gamete interactions are first established between sperm and molecules of the egg jelly coat (JC). Since dejellied oocytes are not normally fertilized, the aim of this study was to determine if the JC of the toad promotes a “capacitating” activity on homologous sperm. We found that preincubation of sperm in Egg Water (diffusible substances of JC, named EW) for 90-180 sec is sufficient to render sperm transiently capable of fertilizing dejellied oocytes. The fertilizing state was related to an increase of tyrosine phosphorylation in sperm proteins from 50 to 200 kDa. Incubation of sperm with Tyrphostin A25 20 µM for 30 min prior to insemination, which inhibited phosphorylation at IC50 of 2 μM, significantly decreased fertilization rates (3.79±2.76%) compared with controls (28.1±3.83%) (p<0.001). Moreover, after incubation of sperm in EW for 15 min, the sperm cholesterol content decreased to 78.9 ± 3.8 %, and preincubation of gametes in cholesterol-3-sulfate 200 nM for 90 min significantly decreased fertilization rates (12.6±2.45%) compared with controls (64.8±0.74%) (p<0.001). The acquisition of sperm fertilizing capacity was shown to be, as in mammals, related to physiological modifications.