Electrophoretic comparisons of liver chromatin proteins isolated from heterotic rats during postweaning development

Stability of liver nuclear proteins in inbred strains of mice

1. A remarkable similarity in the gel patterns of liver nuclear proteins between four inbred strains of mice (A.CA, B10.A, CBA and DBA/2) was observed. 2. Only a very few quantitative differences were detected in the protein spot patterns of nucleoplasmic (spot of about 41 kDa) and chromatin (spot of about 37 kDa) non-histone proteins between those strains of mice. 3. Comparison of two-dimensional gel patterns of non-histone proteins from males and females revealed a few sex-linked spots. Nucleoplasmic protein with molecular weight of about 59 kDa and chromatin proteins with molecular weights of approximately 47 and 57 kDa were more abundant in liver nuclei of male mouse.

Changes of SCE frequency and chromatin molecular composition in rat progeny whose mothers were treated with oral contraceptives in early pregnancy

Wistar female rats were fed with oral contraceptives (OC, containing ethinylestradiolum and methylnorethrindronum) in early pregnancy. The dosage used for rats was 6.6 times more than the clinical dosage for humans in weight per kilogram. The SCE frequencies of liver and ovary cells and the changes of chromatin molecular composition in progeny of the rats fed with OC were observed. The results showed that the liver and ovary cells of newborns 12 h after birth exhibited increased SCEs value (liver: p less than 0.03; ovary: p less than 0.0004). These elevated SCE frequencies declined to the normal level about the 15th day after birth. The results for the quantity of nonhistone (NHP) and chromatin RNA in mother rats and their progenies also exhibited a significant increase, and declined to the normal level at the same period mentioned above. The results suggested that the high level of NHP and chromatin RNA may be induced by OC fed in early pregnancy and be maintained for some time after withdrawal of the OC pills. The changes of the chromatin molecular composition are perhaps somehow related to the increased SCE frequencies in the rat-liver cells. We suggest that the external steroids and their metabolites may activate more genes which were originally inactive and result in increased junctions between euchromatin and heterochromatin, resulting in more SCEs in quickly dividing embryo cells. The report here suggests that during early pregnancy the pills taken by women following OC failures may have a potential mutagenic effect on their progeny for some time after the pills have been stopped.

Comparisons of liver chromatin proteins and template activities in parental and heterotic rats during postweaned development

Electrophoretic profiles of acid-extractable proteins from Holtzman rat liver chromatin display four minor and five major histone bands through certain stages of postweaned development but are qualitatively different from the chromatin protein profiles previously reported during postweaned development for the Fisher 344 rat strain and the F344 X Holtzman heterotic progeny [Tallman, G., et al. (1979). Biochem, Genet. 17:185]. The protein profiles from the heterotic progeny do not reflect and are not combinations of the profiles from the parental strains. Levels of in vitro transcription with Escherichia coli RNA polymerase of total chromatin and of acid-extracted chromatin from Holtzman rat liver tissue fluctuate in an age-specific manner during postweaned development and are higher than previously published levels determined for the Fisher and F344 X H strains during the same developmental period [Tallman, G., et al. (1978). J. Hered. 69:282]. The degrees of stimulation in the transcription assays resulting from the acid treatment vary with the age of the animal but are similar for the maternal Holtzman and hybrid strains. These studies suggest that regulation of heterotic growth may involve dominant, or maternal genetic influences.