Gene dosage effects in human diploid and tetraploid fibroblasts

Tetraploid development in the mouse

Spontaneous duplication of the mammalian genome occurs in approximately 1% of fertilizations. Although one or more whole genome duplications are believed to have influenced vertebrate evolution, polyploidy of contemporary mammals is generally incompatible with normal development and function of all but a few tissues. The production of tetraploid (4n) embryos has become a common experimental manipulation in the mouse. Although development of tetraploid mice has generally not been observed beyond midgestation, tetraploid:diploid (4n:2n) chimeras are widely used as a method for rescuing extraembryonic defects. The tolerance of tissues to polyploidy appears to be dependent on genetic background. Indeed, the recent discovery of a naturally tetraploid rodent species suggests that, in rare genetic backgrounds, mammalian genome duplications may be compatible with the development of viable and fertile adults. Thus, the range of developmental potentials of tetraploid embryos remains in large part unexplored. Here, we review the biological consequences and experimental utility of tetraploid mammals, in particular the mouse.

Relationship between cell size and nuclear volume in nucleated red blood cells of developmentally matched diploid and tetraploid mouse embryos

Analysis of control diploid and polyploid amphibia indicated that cell and nuclear volumes were closely related to their ploidy, so that an increase in ploidy was generally associated with an increase in cell size. This relationship is also believed to occur in mammalian polyploids. However, since the latter are only rarely encountered spontaneously, or only occasionally following experimental manipulation, no detailed morphometric studies have been carried out to date to confirm whether such a relationship exists. In this study, the cellular and nuclear volume of primitive red blood cells was analyzed in carefully developmentally matched control diploid mouse embryos and tetraploid embryos produced by the technique of electrofusion. All of the cells and/or nuclei studied had a characteristic spherical shape which greatly simplified the morphometric analysis. A defined and predictable relationship between ploidy and cellular and/or nuclear volume was observed in the red blood cells between 8.25 and 14.5 days of gestation. During this period the primitive red blood cells are gradually replaced by the definitive erythrocytes. The ratio of control values to tetraploid values was found to be close to the theoretical value of 1:2 when comparable cells and/or their nuclei were analyzed in carefully developmentally matched material.

Growth rate analysis of neurites extended from triploid spinal cord explants

Nerve fibers extending from spinal cord explants of triploid frog tadpoles were analyzed by time-lapse cinephotomicrography. The triploid neurites grew at a mean rate that seemed to reflect the increased chromosomal dosage and had maximal velocities that were several times greater than for diploid neurites. Concurrently, the time between alternating episodes of acceleration and deceleration in triploid neurite elongation phases was decreased. During a 24-h period, however, triploid neurites spent less time elongating with a net result of shorter travel distances than for diploid neurites. The data suggest that the genome is one level of nerve fiber growth control that can be manipulated by dosage alterations.

Changes in nuclear and nucleolar protein content during the growth and differentiation of root parenchyma cells in plant species with different DNA-endoreplication dynamics

Using cytophotometric procedures, we measured the nuclear and nucleolar protein content of successive zones of growth and differentiation in consecutive (1-7 mm) root segments obtained from eight species of the Angiospermae after staining the preparations with Feulgen-Naphthol Yellow S (F-NYS). In meristematic cells the nuclear and nucleolar protein content was found to double during the cell cycle. In species in which differentiation occurs at the same time as nuclear DNA endoreplication, i.e. Vicia faba subsp. minor, V. faba subsp. major, Pisum sativum, Hordeum vulgare and Amaryllis belladonna, the pool of nuclear proteins observed during the G2 phase of the cell cycle was seen in the differentiated zone in nuclei containing 8C DNA. Species in which differentiation is not accompanied by the process of nuclear DNA endoreplication, i.e. Levisticum officinale, Tulipa kaufmanniana and Haemanthus katharinae, exhibited the highest nuclear proteins content during the G2 phase of the cell cycle; comparably high values were not found in the differentiated zone. A decrease in nucleolar protein content was observed during the process of differentiation, this tendency being more evident in the studied species that do not exhibit endoreplication.

Ploidy class-dependent variations during 24 h of glucose-6-phosphate and succinate dehydrogenase activity and single-stranded RNA content in isolated rat hepatocytes

The time-dependent variations over 24 h of glucose-6-phosphate dehydrogenase (G6PDH) activity, succinate dehydrogenase (SDH) activity and single-stranded RNA (ssRNA) content have been investigated by cytophotometric analysis of cytochemically stained isolated hepatocytes of different ploidy classes from adult male rats. A marked variation of 48% over the day in G6PDH activity of the mononuclear diploid cells was revealed, but no significant variation in the binuclear tetraploid cells. The cells of the inbetween ploidy classes showed an amplitude of variation of 38% (binuclear diploid cells) and 24% (mononuclear tetraploid cells), respectively. All cells showed a maximum activity of the enzyme at the middle of the day and a minimum during the night. The relative enzyme activity per mononuclear diploid cell was significantly higher than the relative activity in the other cells, especially at its maximum. The variation of the SDH activity in hepatocytes isolated from the same rats was similar in all cells, irrespective of their ploidy class. The activity was highest at the end of the activity phase of the animals. The SDH activity per cell was directly proportional to the quantity of genome copies. The ssRNA content of the hepatocytes showed a time-dependent variation with a maximum during the resting phase of the animals and a minimum during their activity phase. The variation was larger in the mononuclear diploid cells than in the cells of other ploidy classes and the ssRNA content was also significantly higher in these cells than in the hepatocytes of other ploidy classes when calculated on the basis of genome copies. It is concluded that the large amplitude of variation over the day and the high relative amount of G6PDH activity and ssRNA content in mononuclear diploid cells is related to the function of these cells as stem cells of the liver parenchyma.

Histochemistry and cytochemistry of glucose-6-phosphate dehydrogenase

Histochemistry and cytochemistry of glucose-6-phosphate dehydrogenase has found many applications in biomedical research. However, up to several years ago, the methods used often appeared to be unreliable because many artefacts occurred during processing and staining of tissue sections or cells. The development of histochemical methods preventing loss or redistribution of the enzyme by using either polyvinyl alcohol as a stabilizer or a semipermeable membrane interposed between tissue section and incubation medium, has lead to progress in the topochemical localization of glucose-6-phosphate dehydrogenase. Optimization of incubation conditions has further increased the precision of histochemical methods. Precise cytochemical methods have been developed either by the use of a polyacrylamide carrier in which individual cells have been incorporated before staining or by including polyvinyl alcohol in the incubation medium. In the present text, these methods for the histochemical and cytochemical localization of glucose-6-phosphate dehydrogenase for light microscopical and electron microscopical purposes are extensively discussed along with immunocytochemical techniques. Moreover, the validity of the staining methods is considered both for the localization of glucose-6-phosphate dehydrogenase activity in cells and tissues and for cytophotometric analysis. Finally, many applications of the methods are reviewed in the fields of functional heterogeneity of tissues, early diagnosis of carcinoma, effects of xenobiotics on cellular metabolism, diagnosis of inherited glucose-6-phosphate dehydrogenase deficiency, analysis of steroid-production in reproductive organs, and quality control of oocytes of mammals. It is concluded that the use of histochemistry and cytochemistry of glucose-6-phosphate dehydrogenase is of highly significant value in the study of diseased tissues. In many cases, the first pathological change is an increase in glucose-6-phosphate dehydrogenase activity and detection of these early changes in a few cells by histochemical means only, enables prediction of other subsequent abnormal metabolic events. Analysis of glucose-6-phosphate dehydrogenase deficiency in erythrocytes has been improved as well by the development of cytochemical tools. Heterozygous deficiency can now be detected in a reliable way. Cell biological studies of development or maturation of various tissues or cells have profited from the use of histochemistry and cytochemistry of glucose-6-phosphate dehydrogenase activity.(ABSTRACT TRUNCATED AT 400 WORDS)