Genetic Variants of Plateins (Alveolar Plate Proteins) Among and Within Species of Euplotes1

Abstract

ABSTRACT. In the ciliate Euplotes, each of the sub‐plasmalemmal membranous sacs (the cortical alveoli) encloses a thin polygonal scale or alveolar plate (AP). Adjoining alveoli and their contained plates are tightly integrated into a confluent monolayer that appears to strengthen and help define the shape of the cell cortex. Recently the major proteins making up the AP have been identified. Monoclonal antibodies (MAb) prepared against the AP proteins (termed plateins) of E. aediculatus show reactivity by immunofluorescence with the plates of a wide variety of Euplotes species (including E. eurystomus, E. harpa, E. woodruffi, and E. patella). However, each species tested shows a different pattern of platein bands on immunoblots, in terms of the number and apparent molecular weights (Mr) of the reactive polypeptides. One species (E. gracilis) did not show reactivity with these MAb. Intraspecific platein variants were found within the E. woodruffi complex and among strains of different geographic origin in E. aediculatus. To study the heritability of these platein variants, we used two E. aediculatus clones of different mating type, collected at the same site, that show reproducible differences in the electrophoretic mobility of their lowest Mr platein. Both share common platein bands at 125 kDa and 99 kDa. One clone has its third platein band at 97 kDa, the other clone at 95 kDa. Fourteen F1 clones from matings of these two parental strains have been tested by immunoblotting (using anti‐platein MAb). Each F1 clone has the lower Mr plateins of both parents, and hence displays (in addition to the 125‐kDa band) a triplet of bands (99, 97 and 95 kDa) in this region of the gel/blot, rather than one of the alternative doublets exhibited by either parent clone. The simplest interpretation of these results is that the two lowest Mr plateins represent Mendelian allelic variants, co‐dominant at this level of analysis. No phenotypic differences in cortical structure or properties have yet been noted that might correlate with the identified platein variants.