Differential gene expression in multilocus isozyme systems of the developing green sunfish

The patterns of expression of eight multilocus isozyme systems were investigated in the differentiated adult tissues and the early embryonic stages (0‐210 hours after fertilization) of the green sunfish, Lepomis cyanellus. Enzymes encoded by approximately 23 gene loci were resolved by starch‐gel electrophoresis and detected by specific histochemical staining. The developmental patterns of these isozyme systems appear to be the result of the differential expression of the multiple gene loci. Isozymic forms of glucosephosphate isomerase (GPI‐A₂), malate dehydrogenase (MDH‐A₂), and creatine kinase (CK‐C₂) were present in most differentiated tissues, in the unfertilized egg, and in all stages of embryonic development. Closely homologous forms of these isozymes (GPI‐B₂, MDH‐B₂, and CK‐A₂) were expressed predominantly in skeletal muscle and were first detected at around the time of hatching (38‐42 hours). The similar temporal and spatial patterns of gene expressions for the GPI, LDH, MDH, and CK loci suggest that the duplicate loci encoding isozymes, diverged in their regulation to patterns of differential gene expression which are similar for each enzyme system.