ISOCITRATE DEHYDROGENASE IN MOUSE EMBRYOS: ACTIVITY AND ELECTROPHORETIC VARIATION

Abstract

Using adult mice, Henderson (1965) found that the supernatant, NADP-dependent isocitrate dehydrogenase (IDH) is controlled by a two-allele autosomal locus (Id-l) and that the allelic forms differ in electrophoretic mobility. We report here that the activity of IDH is too low in pre-implanted mouse embryos to detect electrophoretically but that electrophoretic variation is expressed in 12-day embryos. For parents, the following strains of mice were used: adult C3H/HeJ, homozygous for the a allele Id-la/Id-la); DBA/2J, which are homozygous for the b allele; their F1 hybrid C3D2F1 (Id-la/Id-lb); and random-bred albinos with unknown Id-l phenotype. IDH activity was measured fluorometrically (Goldberg, Passonneau & Lowry, 1966) in unfertilized oocytes, one-, two-, and eight-cell embryos, morulae and 3-day blastocysts recovered from the Fallopian tube or uterus of superovulated females and disrupted by one freezing and thawing. The reaction mixture contained 0·2 mm-MnCl2, 0·2 mm-NADP, and 0·2 mm-isocitrate in 50 mm-tris, pH 8·0, in 990 μl with 10 μl of disrupted preimplanted embryos or 10 μl of sample. Analysis of two to seven samples (a total of twenty-nine samples was used) of each of the six different stages with 50 to 300 embryos per sample revealed an average activity of 1·6±0·07×10−12 mole NADP/hr/embryo for all stages. Results have been combined into one group since there was little difference in activity between stages. The level of IDH activ