Increase In Total Cell Volume Research Articles

Ras and rho are required for galphaq-induced hypertrophic gene expression in neonatal rat cardiac myocytes.

The hypertrophic response is characterized by increased myofibril/sarcomere organization, induction of the cardiac specific atrial natriuretic factor (ANF) and myosin light chain-2 (MLC-2v) genes, and an increase in total cell volume. The alpha1-adrenergic agonist phenylephrine induces both the morphological and biochemical markers of hypertrophy in cultured neonatal rat ventricular cardiomyocytes. Previous studies have suggested a functional requirement for the heterotrimeric G-protein, Galphaq, for a subset of the hypertrophic phenotypes. The small GTPases Ras and Rho have also been implicated in phenylephrine-induced hypertrophy. To further delineate the role of Galphaq in hypertrophy, a constitutively active mutant of Galphaq was transiently transfected in primary rat ventricular cardiomyocytes. This molecule was sufficient to induce ANF-, AP1-, and MLC-2-driven gene expression. Co-transfection of Galphaq and dominant negative Ras or dominant negative Raf resulted in dose-dependent inhibition of ANF-driven expression. Both dominant negative Rho, and the Rho inhibitor C3-transferase, also attenuated Galphaq- and Ras-induced ANF-driven gene expression. Cells transfected with active Galphaq did not show a detectable increase in activation of the mitogen activated protein kinases ERK or SAPK. However, activity of the MAP-kinases appears to be important for Galphaq-induced gene expression since the MAP-kinase phosphatase Clone 100 and catalytically inactive SAPK strongly inhibited Galphaq-induced ANF expression. Thus, our studies indicate Galphaq-induced hypertrophic gene expression requires the small G-proteins Ras and Rho. The data also indicates that Galphaq mediated gene expression is dependent on functional MAP-kinases and that multiple signaling pathways contribute to Galphaq-mediated cardiac cell hypertrophy.

Effects of UV-B radiation on synthesis of mycosporine-like amino acid and growth in Heterocapsa triquetra (Dinophyceae)

Unialgal cultures of the dinoflagellate Heterocapsa triquetra (Ehrenberg) Stein were exposed to artificial UV-B radiation and the growth and synthesis of mycosporine-like amino acids (MAAs) were compared with cultures shielded from UV-B radiation by sharp cut-off films. The UV-B radiation did not affect the growth (the increase in total cell volume of the culture) but resulted in an increase in the size of the individual cells and synthesis of MAAs. The synthesis of MAAs during UV-B radiation was synchronised with the cell cycle, being maximal during periods of increases in cell size without division. The absorbance spectra of the MAAs during UV-B radiation changed, showing higher absorption in the UV-B range as compared to the controls.

Early embryogenesis in Arabidopsis thaliana. II. The developing embryo

Embryo differentiation in Arabidopsis thaliana follows the classical Capsella variation of the Onagrad type. Fertilization occurs approximately 3 h after flowering, whereupon vacuolar organization in the zygote changes and the cell elongates rapidly to approximately three times its original length. Cytoplasmic polarization is maintained. During the first two division steps there is very little increase in total cell volume, and during subsequent divisions vacuole number increases, with a concomitant decrease in size. Plastids remain undifferentiated up to the late globular stage, after which grana begin to develop. Ribosomal concentration increases significantly after fertilization. Differences between embryo proper cells become evident by the heart stage; vacuole, plastid, and mitochondrial abundance, size, and complexity vary within the embryo. There are no plasmodesmatal connections with the endosperm or integuments. Suspensor development is complete by the early globular stage, when it consists of seven to nine highly vacuolate cells, each linked by end wall plasmodesmata. Ribosome and volume densities of plastids and mitochondria are significantly lower than in the embryo proper organelles, and dictyosomes are infrequent. Embryo sac wall projections proliferate throughout the micropylar chamber, especially adjacent to the filiform apparatus and zygote base, and ingrowths form on the basal cell proximal wall. Key words: Arabidopsis, embryogenesis, embryo differentiation, wall ingrowths.

Anchorage independence: Analysis of factors affecting the growth and colony formation of wild-type and dl [formula omitted] mutant SV40-transformed lines

We have studied in detail the parameters of anchorage-independent growth of normal rat cells and two clones of simian virus 40 (SV40)-transformed rat fibroblasts. Normal secondary rat embryo fibroblasts (REF) suspended in soft agar neither form large colonies (greater than 0.2-mm in diameter) nor show any appreciable increase in total cell volume. A clone of wild-type SV40-transformed REF grows in agar with a colony-forming efficiency of 54% and an increase in total cell volume greater than 10 3. A clone of REF transformed by the SV40 early deletion mutant 884 has a colony-forming efficiency in agar of only 0.02%, but the total increase in cell volume is greater than 100-fold. In defining anchorage transformants, a distinction must be made between the ability to form large colonies and the ability to undergo a significant number of doublings. Transformation by the viable deletion mutant 884 apparently is impaired far more in the former aspect than in the latter.

Morphogenetic Events in Normal and Synchronously Dividing Tetrahymena

ABSTRACT A study of differentiation in the ectoplasmic cortex of T. pyriformis GL subjected to the standard temperature cycling for the induction of synchronous binary fission has demonstrated an arrest in development which occurs in all cells at a characteristic point in the cell cycle. After treatment all cells were found to possess anarchic fields of kinetosomes in the stomatogenic region, indicating 100 per cent, synchrony. The cells remain in this condition for a period of 50 –55 minutes after the last heat shock. During this time no changes other than in increase in the size of the macronuclear chromatin granules could be detected. At the end of the period of arrested development morphogenesis resumes and binary fission continues in synchrony. The degree of synchrony is somewhat reduced as development proceeds, resulting in about 85 per cent, synchrony at the time of cytoplasmic constriction. In order to facilitate analysis of morphogenesis in synchronously dividing Tetrahymena, a series of four developmental stages has been defined. Based on work which has confirmed available descriptions of stomatogenesis and macronuclear fission, the sequence includes new data on development of the somatic ciliature. All observations, including quantitative consideration of the somatic kinetosomes, ciliary meridians, and contractile vacuole pores has indicated that, aside from synchrony and the period of arrested development, the morphogenetic events in synchronized organisms are fundamentally no different from these processes in untreated cultures. Growth of the organism, growth of the macronucleus, and morphogenesis are to some extent dissociated in synchronized cultures of Tetrahymena. During the heat treatment morphogenesis is blocked while cell and macronuclear growth continues. After treatment and prior to the synchronous cytoplasmic constriction there is a significant increase in mean nuclear volume with no significant increase in total cell volume. After resumption of development in synchronized cultures morphogenesis proceeds unaccompanied by any increase in cellular volume. In addition, it is believed that the nuclear increase occurs during the period of arrested development and not during the subsequent period of development. The use of protargol staining promises to be of value in studies of ciliate morphogenesis. Of those structures in and on the ciliate cortex, protargol appears to be highly specific for kinetosomes. In addition to this the cilia and ciliary membranes are revealed by this technique.

THE CHANGE IN OSMOTICALLY INACTIVE FRACTION PRODUCED BY CELL ACTIVATION

1. Resting and activated eggs of the sea urchin Arbacia punctulata were swollen in hypotonic sea water (60, 70, 80, and 90 per cent), and allowed to attain equilibrium volumes (Figs. 1 and 2). 2. Both fertilized and unfertilized eggs obey the Boyle-van't-Hoff law, but the value for b, the "osmotically inactive fraction" or non-swellable volume, was different for the two, averaging in the cases studied 7.3 per cent for unfertilized and 27.4 per cent for fertilized. 3. On activation, the eggs of the sea urchin undergo a definite increase in total cell volume, of approximately 2.7 per cent. 4. Some evidence is adduced for the possibility that the alteration in cell volume and in o.i.f. may depend upon the species in question. 5. A parallelism between change in b and alteration of respiratory metabolism in Arbacia, Chaetopterus, and Arbacia fragments is pointed out. This requires further investigation in other species to establish generality. 6. Equations for the calculation of the point at which osmotic pressures and cell volumes are identical for unfertilized and fertilized eggs are included. 7. A mechanical analogue of the phenomena is introduced (Fig. 3).

Studies on cell number and the progression factor in the growth of Japanese beetle larvae (Popillia japonica Newman)

AbstractIncreases in weight, total body length, and width and length of the head capsule of Japanese beetle larvae were studied. Since the progression factors decreased with succeeding molts and exhibited considerable variation it was concluded that Przibram's principle is inapplicable. Cells were counted in the mid‐intestine and brain. Columnar cells of the mid‐intestine were measured. The data show: (a) No increase in cell number occurs at the time of molting. (b) The progression in weight and length cannot be correlated with an increase in cell number. In the first instar the progression for increase in weight was 5.73; while for increase in cell number, it was 1.67 for the mid‐intestine, and 1.19 for the brain. In the second instar, the corresponding figures were 5.24, 1.98 and 1.69. In the third instar average weight increased 3.18 times, but there was practically no increase in cell number. Thus, molting does not represent a definite increase in number of cells of the insect's body as suggested by Przibram and Megusar, and Bodenheimer's method of calculating cell divisions seems to have no factual basis. Increase in size of the larva is largely due to an increase in cell size. The ratio of increase in total cell volume of the columnar cells of the mid‐intestine is approximately equal to the ratio of weight increase.