The ontogeny of creatine kinase (CK) in Brachydanio rerio, B. albolineatus and hybrids formed by their reciprocal crosses was investigated using electrophoretic and spectrophotometric methods. Creatine kinase existed in three homodimeric isozymes in tissues of both species: a n eye-brain predominant CK-B, form, a skeletal muscle predominant CK-A, form, and a stomach specific CK-C, form. Zebra and pearl danio embryos exhibited identical progressions of CK isozymes through four days postfertilization. The CK-B, isozyme was continuously expressed and was the only CK form present from Stage 1 (fertilization) through Stage 20 (optic cup). The CK-A, isozyme initially appeared a t Stage 21. Its expression correlated temporally with slow, irregular contractions of the trunk and early differentiation of the trunk somites into myoblasts. Spectrophotometric analysis of total CKshowed a sharp decline in activity during the first 10 hours of development Le., until the end of gastrulation). Total CK activity remained low until the appearance of the CK-A2 isozyme.
Embryos of reciprocal crosses between B. rerio and B. albolineatus displayed
similar patterns of expression of both CK-B2 and CK-A2 isozymes. The paternal Ck-B locus was first expressed in hybrid embryos at 48 hours postfertilization in the form of the CK-BABR heterodimer. The paternal CK-B, homodimer was detected in embryos at 55 hours postfertilization. The parental alleles of the Ck-B locus were synchronously expressed. The pattern of CK-A, expression in hybrids followed a pattern similar to that in intraspecific crosses.
Experiments with actinomycin D and cycloheximide supported our previous