ROLE OF OVIDUCTAL PARS RECTA EXTRACT ON INTERSPECIFIC FERTILIZATION BETWEEN ANURANS

During their journey through the oviductal pars recta, the vitelline e nvelope (VE) of Bufo arenarum oocytes encounter structural alterations that make them sensitive to attack by sperm lysin and thus to penetra tion by sperm cells. The role of pars recta (PR) on the specificity of fertilization between amphibians was analyzed by conditioning Bufo ar enarum oocytes with either homologous PR extract (PRE) or Leptodactylu s chaquencis PRE. The oocytes were thereafter exposed to sperm lysin p reparations from both species. Lysis of the VE only took place when th e oocytes were exposed to the homologous PRE. The pattern of protein c omposition of PRE of these species was strikingly different as shown b y Coomassie blue staining oi SDS-PAGE. Moreover, antibodies against PR fluid (PRF) of Bufo arenarum produced seven bands of immunoprecipitat ion in electrophoresed homologous PRE and only one faint band in Lepto dactylus chaquencis PRE. Here we show that: (i) the biological activit y of PR from Bufo arenarum and Leptodactylus chaquencis over the VE of Buio arenarum oocytes is species-specific; (ii) this specificity seem s to be based in differences in protein structure, which was indicated by the fact that proteins from PRE of Leptodactylus chaquencis and Bu fo arenarum were antigenically distinct; (iii) the specificity was sol ely related to PR activity and not to sperm lysin activity since sperm lysin preparations from both species showed comparable activity.