Identification and localization of α- and β-spectrins in oocytes of three Antarctic teleosts:: Trematomus bernacchii, Trematomus newnesi (Nototheniidae) and Chionodraco hamatus (Channichthyidae)

The presence and localization of alpha- and beta-spectrins and of the spectrin cross-linking protein actin were investigated, in previtellogenic oocytes of three species of Antarctic teleosts: the two red-blooded nototheniids, Trematomus bernacchii and Trematomus newnesi, and the channichthyid, the ice fish Chionodraco hamatus. Analyses by western blotting indicated that these species had an unusual abundance of spectrin isoforms and that they were characterized by rather low molecular masses. The immunocytochemistry in situ demonstrated that alpha- and beta-spectrins showed a variable pattern of localization that clearly depended on both the species considered and the stage of oocyte differentiation. In particular, the two Trematomus spp. showed a distribution of spectrins absolutely comparable and rather different from that of C. hamatus. The evidences collected confirmed that channichthyids have isolated early from the group of red-blooded species and suggest that in notothenioids significant changes might have occurred in spectrin genes and in their protein products.