Creatine kinase isozymes in pipid frogs: Their genetic bases, gene expressional differences, and evolutionary implications

Abstract

AbstractPipid frogs possess a creatine kinase isozyme repertory with a complexity paralleled only by teleostean fish. The effects of allelic polymorphism on their isozymes as well their differential solubility and resistance to heat denaturation suggest that species of Xenopus have at least four different CK loci. Each locus has its own tissue pattern of expression. CK‐I isozymes are found only in the eye and stomach of Xenopus, in the stomach but not the eyes of Pipa and Hymenochirus, and the latter appears to have this isozyme in the liver also. The tissue expression of CK‐II and CK‐IV, respectively, resembles that of CK‐A and CK‐C of fish and that of CK‐M (muscle) and CK‐B (brain) of higher vertebrates. CK‐III shows a striking developmental transition. In Xenopus heart muscle, additional CK isozymes are present that do not appear to be heterodimers. These may represent the contributions of additional creatine kinase genes or of epigenetic modification of other isozymes.The general tissue patterns of isozyme expression are similar but unique for each Xenopus species. The presumed allotetraploid species have essentially the same number of CK isozymes as the diploid X. tropicalis, suggesting a loss of duplicate gene expression or a cryptic expression due to coincident isozyme mobilities. It is possible that certain double banded isozymes in X. borealis and X. gilli represent the expressions of genes from a past polyploidization event.Two other genera of Pipidae, Hymenochirus and Pipa, differ from Xenopus in that they lack the CK‐III isozyme, and that the relative electrophoretic mobilities of the CK‐II and CK‐IV isozymes are reversed.