Enzyme ontogeny in normal and hemimelic limbs of mice.

The appearance of electrophoretically separable isozyme patterns is specific both to type of tissue and to its stage of development (Markert & Moller, 1959). In abnormally developing embryonic systems there are alterations in the time of initial appearance and the persistence of isozymes from a variety of metabolic areas (Johnson & Spinuzzi, 1966, 1968). In malformed embryos from folic-aciddeficient rats the altered zymogram patterns of esterases from abnormal limbs were different from those of abnormal kidneys, yet differentiation of zymograms from the normal hearts of these embryos was unaltered. This implies a correlation between altered tissue-specific zymogram patterns and abnormally developing systems, though no causal relationship has as yet been shown (Johnson, 1968). Moreover, when tibial hemimelia in the rat was elicited by two different teratogens—a folic acid antagonist, 9-methylpteryol-glutamic acid (PGA), and the alkylating agent iV-nitroso-JV-methylurea (NNMU)—there were similar changes in the non-specific esterases after electrophoretic separation of homogenates from the defective limbs (Johnson & Lambert, 1968). Dagg (1960, 1967) was able to elicit tibial hemimelia in C57BL/10 mice with an injection of 500/^g 5-fluorouracil (5-FU) on the tenth day of gestation. This defect was structurally indistinguishable from that produced by the homozygous luxate gene (Ixjlx) (Carter, 1951). A dose of 250 fig 5-FU produced polydactyly, the phenotype of Ixj + mice, and tibial hemimelia was produced when 250 fig 5-FU was given to females carrying heterozygous embryos. The present study was designed to determine whether the enzymic ontogeny is similar for the homozygous mutant luxate and the 5-fluorouracil-induced defect, and whether or not any interaction of the effects of the genes and chemical agents could be detected by electrophoretic techniques. The enzymes included alkaline phosphatases, which have been found characteristically in the apical ectoderm ridge of the limb bud (Milaire, 1962), adenosine monophosphatases, which are active in interdigital areas (Milaire, 1965), non-