Quantitative Assay of Cyclin-Dependent Kinase Activity As a Sensitive Marker of Cell Proliferation in Marine Teleost Larvae

An evolutionarily conserved family of cyclin-dependent kinases (Cdks) regulates cell cycle progression in eukaryotes. Mitosis-promoting factor (MPF) is a transiently activated Cdk required for mitosis. We propose use of partially purified MPF kinase activity as a sensitive marker of cell proliferation in marine teleost larvae and describe a quantitative spin-filter assay of suc1-precipitated MPF activity. MPF extracted from embryos and larvae of red drum, Sciaenops ocellatus, phosphorylated histone H1 protein and a Cdk-specific peptide substrate. Kinetic analyses demonstrated that apparent K _m values of red drum MPF for adenosine triphosphate and the peptide substrate were 98.3 and 18.2 μM, respectively. A simple growth experiment showed that MPF activity was significantly greater in rapidly growing red drum larvae than in intermittently fed cohorts growing more slowly. Received July 23, 1998; accepted January 14, 1999