ABSTRACT
The smooth muscle cell population in major arteries of humans and experimental animals is heterogeneous with regard to cellular DNA content. A proportion of cells has polyploid DNA content and this proportion increases with normal aging and with hypertension. We have isolated pure populations of rat aortic smooth muscle cells containing 2C, 4C, and 8C DNA content by cloning of cultures of cells previously subjected to flow cytometric cell sorting. Karyologic analysis of these clonal populations revealed them to be pure diploid, tetraploid, and octaploid populations, respectively, containing 2N (= 42), 4N, and 8N chromosomes. Cell attachment area and nuclear size appeared to increase with the level of ploidy. Studies of the proliferative characteristics of the cells revealed that the growth rate and ultimate cell densities achieved decreased as the ploidy level increased. The intrinsic cellular radiosensitivity of these clones did not vary with ploidy. Increased smooth muscle cell ploidy is, therefore, associated with a decreased rate of proliferation. The emergence of smooth muscle cells with polyploid DNA content under normal and pathologic conditions is probably due to mitotic polyploidization without net cell proliferation and may be related to the need for expression of differentiated functions.
Subject(s)
Cell Cycle , Muscle, Smooth, Vascular/physiology , Ploidies , Animals , Aorta, Thoracic , Cell Division , Cell Separation , Cell Survival/radiation effects , Clone Cells/classification , Clone Cells/radiation effects , DNA/metabolism , Diploidy/radiation effects , Male , Muscle, Smooth, Vascular/cytology , Muscle, Smooth, Vascular/radiation effects , Ploidies/radiation effects , Rats , Rats, Inbred StrainsABSTRACT
As the level of ploidy rises in Pullularia pullulans, this causes an increase in the frequency of spontaneous and UV-induced auxotrophic mutants as well as mutants with a modified respiration activity while the frequency of morphological mutants decreases. The latter can arise as a result of recessive and dominant mutations. A higher frequency of morphological mutants in the haploid may be result of recessive mutations. It is likely that the frequency of dominant mutations increases in cultures with a higher level of ploidy since, as the difference between the frequency of UV-induced mutants and the frequency of spontaneous morphological mutants increases.
Subject(s)
Mitosporic Fungi/genetics , Mutation , Ploidies/radiation effects , Diploidy/radiation effects , Haploidy/radiation effects , Mutation/radiation effects , Polyploidy/radiation effects , Ultraviolet RaysABSTRACT
Strains of Salmonella typhimurium which contain a duplication of approximately 30% of the genome may be obtained by a simple selective procedure. These strains are highly unstable, losing the duplication when grown on non-selective medium. In this paper we report that treatment of merodiploid bacteria with mutagenic agents stimulates the rate at which haploid segregants are obtained from merodiploid strains. The mutagens which have been tested for this effect are X-rays, ultraviolet light (UV), ethyl methanesulfonate (EMS), and the azaacridine half-mustard ICR-372.
