Locus-dependent profiles of the rescue of nonexcitable behavioral mutants during conjugation in Paramecium caudatum

Abstract

Non-excitable mutants of Paramecium caudatum, CNR (caudatum non-reversal) are unable to show the avoiding reaction due to the malfunction of voltage dependent Ca2+ channels. CNR mutants are divided into four complementation groups and are controlled by four genes at different loci: cnrA, cnrB, cnrC, and cnrD. When CNR mutants are mated with the wild type, the mutant cell temporarily expresses the wild-type phenotype (called conjugation rescue). Transfer of diffusible wild-type gene products to the mutant mate through cytoplasmic connections is thought to be the cause of this phenomenon. Excitability of mutant cells during conjugation with wild type or other mutants controlled by different loci, and immediately after pair separation was examined by K+ test solution. Restorations of excitability in CNR mutants show distinguishable characters depending upon the different loci. cnrC showed wild type character indistinguishable from wild-type cells soon after pair formation. cnrD showed clear conjugation rescue but never reached the level of wild-type cells. cnrA showed only slight conjugation rescue immediately after pair separation. cnrB never showed conjugation rescue.