New evidence of anuran oviducal pars recta involvement on gamete interaction

Abstract

AbstractCoelomic oocytes of the toad Bufo arenarum are not fertilizable when inseminated in egg water that assures fertilization of dejellied uterine eggs. However, when coelomic oocytes were pretreated with an extract from oviducal pars recta (PRE) and inseminated in egg water, a high frequency of fertilization was obtained.In this study the effect of PRE on acrosome breakdown (AB) was studied by means of vitelline envelope (VE) lysis and fertility tests with B. arenarum sperm, and by direct observations with the light microscope of the AB with Leptodactylus chaquensis sperm. The coelomic envelope becomes sensitive to lysin solution only after PRE treatment. The addition of sperm to PR‐treated oocytes, in a medium containing egg water, resulted in a marked swelling and softening of the VE. But this lytic effect by sperm can be observed only when egg water was present in the medium. These results indicate that jelly‐molecules are necessary for the acrosome process to begin and that PR components engulfed in the VE are not capable of inducing AB by themselves. Likewise, incubation of B. arenarum sperm with PRE did not impair their fertilizing capacity and the supernatant of this incubation medium did not have typical VE lytic activity.Moreover, when the effect of PRE on AB was studied by direct observation of L. chaquensis sperm, it was found that PRE neither induces AB nor modifies its time‐course.