title: The development of polyploidy in two classes of rat liver nuclei.
abstract: Two classes of nuclei from livers of Sprague-Dawley rats were isolated, one pelleting in 2.3 M sucrose (H nuclei) and the second class sedimenting through 1.6 and 1.8 M sucrose and banding at the 1.8/2.3 M sucrose interface (L nuclei) of a three-step discontinuous gradient. In younger animals, the L nuclear fraction was the major fraction, but the percentage of nuclei found in the L fraction decreased as the animals grew. Nuclear ploidy was determined by flow microfluorometry using propidium iodide as a DNA stain. Both the H and L nuclear fractions contained diploid, tetraploid and octaploid nuclei; but the degree of polyploidy was greater in the H fraction. Concomitant with the change in distribution of nuclei between the H and L fractions with increasing age was a progressive increase in the degree of polyploidy  in the H fraction. Polyploidy did not increase linearly with age in the H nuclear fraction but increased in cycles marked by large changes in the numbers of nuclei found in H and L nuclear fractions. By 12 weeks of age, 4n-H nuclei were the largest single population of nuclei in rat liver. These observations suggested that the shift of liver nuclei from the L fraction to the H fraction was associated with the development of polyploidy and with the differentiation of hepatocytes.
mesh_terms: D000375:Aging; D000818:Animals; D002458:Cell Fractionation / Q000379:methods; D002467:Cell Nucleus / Q000648:ultrastructure; D002499:Centrifugation, Density Gradient / Q000379:methods; D005260:Female; D008099:Liver / Q000254:growth & development* / Q000648:ultrastructure; D008297:Male; D011123:Polyploidy; D051381:Rats; D012737:Sex Factors