Spectrin and Ankyrin-like Proteins in the Egg of Discoglossus pictus (Anura): Their Identification and Localization in the Site of Sperm Entrance versus the Rest of the Egg: (spectrin/ankyrin/anuran eggs/fertilization).

The Discoglossus pictus egg has a specific site of sperm-egg interaction, the dimple, which has a well-defined cytoskeleton. We studied whether there are cytoskeletal and cytoskeleton-related proteins typically involved in the polarization of plasma membrane proteins. The identity and the localization of the molecules cross-reacting with antispectrin, antifodrin and antiankyrin antiobodies were investigated by immunofluoresecence and immunoblotting of the proteins of the dimple (D) and of the rest of the egg (dimple-less-egg; DLE). Two polypeptides of about 254-and 246-kD were detected in the D and DLE, and localized in the egg cortex. A third molecule, weakly cross-reacting with antispectrin and antifodrin, was found in the subcortical cytoplasm. The 246-kD polypeptide was labile in samples prepared for SDS-PAGE; a mild prefixation of eggs prevented its dispersion. Mild fixation was also needed to retain antispectrin reactivity in cryostat sections of the DLE cortex, while this is not necessary in D. A molecule of about 204-kD, cross-reacting with antiankyrin, was detected in the cortex of the whole egg. These data and the finding that the concentrations of both the 254-kD polypeptide and ankyrin are about 12-fold higher in D than in the DLE, suggest that, in D, spectrin has a specific organization.