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At least 19 recordsLinked to original sources
PubMed2002

A bird's-eye view of the C-value enigma: genome size, cell size, and metabolic rate in the class aves.

For half a century, variation in genome size (C-value) has been an unresolved puzzle in evolutionary biology. While the initial "C-value paradox" was solved with the discovery of noncoding DNA, a much more complex "C-value enigma" remains. The present study focuses on one aspect of this puzzle, namely the small genome sizes of birds. Significant negative correlations are reported between resting metabolic rate and both C-value and erythrocyte size. Cell size is positively correlated with both nucleus size and C-value in birds, as in other vertebrates. These findings shed light on the constraints acting on genome size in birds and illustrate the importance of interactions among various levels of the biological hierarchy, ranging from the subchromosomal to the ecological. Following from a discussion of the mechanistic bases of the correlations reported and the processes by which birds achieved and/or maintain small genomes, a pluralistic approach to the C-value enigma is recommended.

Animals↗
PubMed1999

Regulation of imaginal disc cell size, cell number and organ size by Drosophila class I(A) phosphoinositide 3-kinase and its adaptor.

BACKGROUND: Class I(A) phosphoinositide 3-kinases (PI 3-kinases) have been implicated in the regulation of several cellular processes including cell division, cell survival and protein synthesis. The size of Drosophila imaginal discs (epithelial structures that give rise to adult organs) is maintained by factors that can compensate for experimentally induced changes in these PI 3-kinase-regulated processes. Overexpression of the gene encoding the Drosophila class I(A) PI 3-kinase, Dp110, in imaginal discs, however, results in enlarged adult organs. These observations have led us to investigate the role of Dp100 and its adaptor, p60, in the control of imaginal disc cell size, cell number and organ size. RESULTS: Null mutations in Dp110 and p60 were generated and used to demonstrate that they are essential genes that are autonomously required for imaginal disc cells to achieve their normal adult size. In addition, modulating Dp110 activity increases or reduces cell size in the developing imaginal disc, and does so throughout the cell cycle. The inhibition of Dp110 activity reduces the rate of increase in cell number in the imaginal discs, suggesting that Dp110 normally promotes cell division and/or cell survival. Unlike direct manipulation of cell-cycle progression, manipulation of Dp110 activity in one compartment of the disc influences the size of that compartment and the size of the disc as a whole. CONCLUSIONS: We conclude that during imaginal disc development, Dp110 and p60 regulate cell size, cell number and organ size. Our results indicate that Dp110 and p60 signalling can affect growth in multiple ways, which has important implications for the function of signalling through class I(A) PI 3-kinases.

Animals↗
PubMed1999

PTEN affects cell size, cell proliferation and apoptosis during Drosophila eye development.

Mutations in the tumor suppressor gene PTEN (MMAC1/TEP1) are associated with a large number of human cancers and several autosomal-dominant disorders. Mice mutant for PTEN die at early embryonic stages and the mutant embryonic fibroblasts display decreased sensitivity to cell death. Overexpression of PTEN in different mammalian tissue culture cells affects various processes including cell proliferation, cell death and cell migration. We have characterized the Drosophila PTEN gene and present evidence that both inactivation and overexpression of PTEN affect cell size, while overexpression of PTEN also inhibits cell cycle progression at early mitosis and promotes cell death during eye development in a context-dependent manner. Furthermore, we have shown that PTEN acts in the insulin signaling pathway and all signals from the insulin receptor can be antagonized by either Drosophila or human PTEN, suggesting a potential means for alleviating symptoms associated with altered insulin signaling.

Amino Acid Sequence↗
PubMed1998

Cell size, cell cycle, and alpha-smooth muscle actin expression by primary human lung fibroblasts.

Primary human lung fibroblasts were separated into small (group I), intermediate (group II), and large (group III) subpopulations by unit gravity sedimentation (1 G). The three subsets retained differences in cell size for up to 15 days of primary culture. Flow cytometric (fluorescence-activated cell sorter) measurements of forward-angle light scatter agreed well with fibroblast volume measured by image analysis and confirmed the utility of forward-angle light scatter for discriminating size subpopulations. Group II fibroblasts accumulated most rapidly by 8 days of culture and also contained the greatest proportion of S and G2/M phase cells as determined by fluorescence-activated cell sorter. Fibroblasts that were immunoreactive with antibodies to alpha-smooth muscle actin (alpha-SMA) were found only in group III. In situ end labeling of fragmented DNA detected apoptotic cells in both groups II and III, but double labeling for in situ end labeling and alpha-SMA revealed apoptotic cells in both the alpha-SMA-positive and -negative populations. These results demonstrate that primary human lung fibroblasts behave as predicted by classic models of cell cycle progression and differentiation. However, they do not support the hypothesis that the expression of alpha-actin is related to apoptosis. We also describe a simple and reproducible method for the high-yield isolation of human lung fibroblast subsets of differing proliferative potential and phenotype.

Actins↗
PubMed1996

The role of the cortical cytoskeleton: F-actin crosslinking proteins protect against osmotic stress, ensure cell size, cell shape and motility, and contribute to phagocytosis and development.

We generated Dictyostelium double mutants lacking the two F-actin crosslinking proteins alpha-actinin and gelation factor by inactivating the corresponding genes via homologous recombination. Here we investigated the consequences of these deficiencies both at the single cell level and at the multicellular stage. We found that loss of both proteins severely affected growth of the mutant cells in shaking suspension, and led to a reduction of cell size from 12 microns in wild-type cells to 9 microns in mutant cells. Moreover the cells did not exhibit the typical polarized morphology of aggregating Dictyostelium cells but had a more rounded cell shape, and also exhibited an increased sensitivity towards osmotic shock and a reduced rate of phagocytosis. Development was heavily impaired and never resulted in the formation of fruiting bodies. Expression of developmentally regulated genes and the final developmental stages that were reached varied, however, with the substrata on which the cells were deposited. On phosphate buffered agar plates the cells were able to form tight aggregates and mounds and to express prespore and prestalk cell specific genes. Under these conditions the cells could perform chemotactic signalling and cell behavior was normal at the onset of multicellular development as revealed by time-lapse video microscopy. Double mutant cells were motile but speed was reduced by approximately 30% as compared to wild type. These changes were reversed by expressing the gelation factor in the mutant cells. We conclude that the actin assemblies that are formed and/or stabilized by both F-actin crosslinking proteins have a protective function during osmotic stress and are essential for proper cell shape and motility.

Actinin↗
PubMed1985

Growth rate and life spain in Drosophila. IV. Role of cell size and cell number in the biphasic relationship between life span and growth rate.

The patterns of variation of wing cell size and number were studied under developmental conditions leading to a biphasic relationship between life span and growth rate while duration of development remained constant (development on an agar-only medium with a varying added yeast amount, constant temperature (25 degrees C) and constant larval density). Across the yeast range, a 125% increase of body weight was accompanied by a roughly 30% increase in the wing linear dimensions, wing cell size and wing cell number while estimated duration of cell division and its reciprocal mitotic division rate remained constant. Furthermore, cell size (but not cell number) varied with growth rate in a similar biphasic pattern to that observed for life span. Finally, from a simultaneous examination of the covariation patterns of life span, growth rate, cell size and cell number with decreasing yeast amount, it became apparent that there was a "critical" yeast amount, approximately 125 mg/120 eggs, below which: (a) cell number abruptly started to decrease linearly from a roughly constant value; (b) the rate of the slow decrease of cell size now tripled and that of growth rate increased even more; and (c) life span which, in the upper yeast range, increased slowly with decreasing yeast, apparently reached a maximum at the critical yeast level and decreased three times faster below that level. These data taken together suggest that: (i) the decrease of all parameters (including life span) below the critical yeast level results from a presumably suboptimal or disturbed development because of and in proportion to the lack of nutrients and (ii) the increase of life span with decreasing yeast amount above the critical yeast level has not been definitely explained but some possibilities are suggested such as changes in subcellular organelle numbers, size and/or functional properties, or other changes due to a phenomenon equivalent to food restriction in rats, probably without changes in overall metabolic rate of the flies.

Aging↗
PubMed2003

Do genetic make-up and growth manipulation affect tomato fruit size by cell number, or cell size and DNA endoreduplication?

This work investigated the link between genetic and developmental controls of fruit size and composition. On two isogenic lines (CF12-C and CF14-L), differing by fruit weight and sugar content quantitative trait loci (QTLs) identified previously, basal and tip fruits were characterized at anthesis and at maturity through their growth, dry matter and sugar content, number and size of cells and nuclei DNA content. The influence of competition was assessed by removing either basal or tip ovaries at anthesis. On an intact inflorescence, CF12-C fruits grew less than CF14-L fruits, with 1.67 fewer cell layers and similar cell size, suggesting that genes controlling cell division may be responsible for this fruit size variation. Truss thinning masked the QTL effect on fruit size, mainly by reducing the difference in cell number between the two lines and by promoting cell expansion in tip fruits, so that fruit growth was similar at both positions and for both lines. Thus, in these lines, cell number exerts a control on final fruit size only when there is competition among fruits. Different responses of basal and tip fruits after flower removal suggested that this treatment induced changes in hormonal relationships within the truss. No fixed relationship between DNA endoreduplication and cell size was found, as while cell size and dry matter and sugar contents differed with tomato lines, fruit position and truss size, endoreduplication patterns were the same. CF12-C fruits had a higher dry matter (+0.3% of fresh weight) and carbohydrates (+8% of dry matter) content than CF14-L fruits. The percentage dry matter was independent of truss size but decreased slightly from basal to tip fruits.

Cell Count↗
PubMedDate not supplied

Cell size and cell type analysis of calcitonin gene-related peptide-containing cutaneous and splanchnic sensory neurons in the rat.

Cell size, cell type and calcitonin gene-related peptide (CGRP)-like immunoreactivity were compared between cutaneous and splanchnic sensory neurons by means of a combination of fluorescent tracer and immunohistochemistry. Nineteen percent of cutaneous sensory neurons and 88% of splanchnic sensory neurons were shown to contain CGRP. The former cells were larger than the latter ones, which was also confirmed by the finding that about a half of the former cells contained 200 kDa subunit of neurofilament protein, while only 8% of the latter ones were positively stained. These findings suggest that most of the visceral CGRP-IR sensory neurons are small type B.

Animals↗
PubMed1993

The relationship between cell size and cell fate in Volvox carteri.

In Volvox carteri development, visibly asymmetric cleavage divisions set apart large embryonic cells that will become asexual reproductive cells (gonidia) from smaller cells that will produce terminally differentiated somatic cells. Three mechanisms have been proposed to explain how asymmetric division leads to cell specification in Volvox: (a) by a direct effect of cell size (or a property derived from it) on cell specification, (b) by segregation of a cytoplasmic factor resembling germ plasm into large cells, and (c) by a combined effect of differences in cytoplasmic quality and cytoplasmic quantity. In this study a variety of V. carteri embryos with genetically and experimentally altered patterns of development were examined in an attempt to distinguish among these hypotheses. No evidence was found for regionally specialized cytoplasm that is essential for gonidial specification. In all cases studied, cells with a diameter > approximately 8 microns at the end of cleavage--no matter where or how these cells had been produced in the embryo--developed as gonidia. Instructive observations in this regard were obtained by three different experimental interventions. (a) When heat shock was used to interrupt cleavage prematurely, so that presumptive somatic cells were left much larger than they normally would be at the end of cleavage, most cells differentiated as gonidia. This result was obtained both with wild-type embryos that had already divided asymmetrically (and should have segregated any cytoplasmic determinants involved in cell specification) and with embryos of a mutant that normally produces only somatic cells. (b) When individual wild-type blastomeres were isolated at the 16-cell stage, both the anterior blastomeres that normally produce two gonidia each and the posterior blastomeres that normally produce no gonidia underwent modified cleavage patterns and each produced an average of one large cell that developed as a gonidium. (c) When large cells were created microsurgically in a region of the embryo that normally makes only somatic cells, these large cells became gonidia. These data argue strongly for a central role of cell size in germ/soma specification in Volvox carteri, but leave open the question of how differences in cell size are actually transduced into differences in gene expression.

Animals↗
PubMed1998

Protoporphyrin IX accumulation in cells treated with 5-aminolevulinic acid: dependence on cell density, cell size and cell cycle.

Human colon adenocarcinoma cells (WiDr) and Chinese hamster lung fibroblasts cells (V79) were incubated with different concentrations of 5-aminolevulinic acid (ALA), and the production of protoporphyrin IX (PpIX) was studied using several techniques. The amount of PpIX produced per cell increased with increasing ALA concentration according to different kinetics for the 2 cell lines. For both cell lines a cell density dependency of the PpIX synthesis was observed. For saturating ALA concentrations, 2-3 times more PpIX was produced per cell at a density of 5 x 10(4) than at a density of 5 x 10(3) cells/cm2. The photosensitivity of cells appeared to increase even more than the PpIX content, indicating a cooperative effect in inactivation. The PpIX production rate increased with cell size and was about 1.9 times higher for cells in the G2 + M phase than for cells in the G1 phase of the cell cycle. Neither cell size nor cell cycle distribution were significantly dependent on cell density.

Adenocarcinoma↗
PubMed1999

Drosophila S6 kinase: a regulator of cell size.

Cell proliferation requires cell growth; that is, cells only divide after they reach a critical size. However, the mechanisms by which cells grow and maintain their appropriate size have remained elusive. Drosophila deficient in the S6 kinase gene (dS6K) exhibited an extreme delay in development and a severe reduction in body size. These flies had smaller cells rather than fewer cells. The effect was cell-autonomous, displayed throughout larval development, and distinct from that of ribosomal protein mutants (Minutes). Thus, the dS6K gene product regulates cell size in a cell-autonomous manner without impinging on cell number.

Animals↗
PubMed1987

Regulation of G2 by cell size contributes to maintaining cell size variability within certain limits in higher plants.

The variability of (1) surface area projection (size) at which cells terminate DNA replication, (2) the area at which they initiate mitosis, (3) the area at which they divide, (4) the duration of G2, and (5) the duration of G2 plus mitosis (in fact, prophase + metaphase + anaphase) has been estimated in steady-state cell populations of Allium cepa root meristems. The coefficient of variation of cell area at termination of DNA synthesis was found to be 14% while the coefficient of variation of cell area at mitosis initiation was 13%. As there is also a substantial variability of G2 (the coefficient of variation was estimated to be 38%), the combination of these data indicates that cell size regulation of G2 contributes to maintaining cell size variability (and therefore DNA concentration) within certain limits. Mitosis also varies but less than G2 (the coefficient of variation of G2 + mitosis was found to be 31%). As the coefficient of variation of cell area at division (14%) is hardly larger than the coefficient of variation of cell area at initiation of mitosis, it can be suggested that coordination between cell size and mitosis duration helps to avoid a significant increase in the variability of cell size at the end of the division cycle.

Allium↗
PubMed1976

Cell size and mutual cell adhesion. II. Evidence for a relation between cell size, long-range electrostatic repulsion and intercellular adhesiveness during density-regulated growth in suspension.

The strength of the long-range electrostatic repulsion forces on HeLa cells is measured by agglutinative titration using low molecular weight polylysine (M.W. 11,000). Repulsion forces, found to be present on the smaller HeLa cells from density-inhibited suspension cultures, are weakened by incubation of the cells in hypotonic NaCl solutions. Repulsion forces, found to be absent on the larger cells from fast growing cultures, can be induced on these cells by incubation in hypertonic NaCl solutions. Both effects of anisotonicity are reversible, and disappear on restoration of the medium to normal tonicity. Induction of repulsion forces on fast growing cells is prevented by previous treatment of the cells with neuraminidase. Neuraminidase also abolishes repulsion on density-inhibited cells. It is proposed that alterations of the cell size, produced by anisotonicity or occurring during growth in isotonic suspension medium, affect mutual cell adhesiveness by modifying the strength of the repulsion forces generated by cell surface sialic acids.

Agglutination Tests↗
PubMed1979

Cell size and cell division of the anterior pituitary: time course in the growing rat.

Pituitary cells increase their numbers more than 3-fold during the 1st 10 days of life while maintaining the same cell size ratios. In the 25-day-old animal, the rate of cell division slows and there is a slight increase in the number of large cells. An increase in adult weight is attributed to hyperplasia and a shift to a population of larger cells.

Aging↗
PubMed1985

Epidermal tissue homeostasis. I. Cell pool size, cell birth rate and cell loss by moulting in the intact toad, Bufo bufo.

Toad epidermis is a suitable model for studies on tissue homeostasis because cell pool size, influx into and efflux from the cell pool can be easily determined. The cell pool size was obtained by cell counting on photomicrographs, the influx (cell birth rate) was assessed by the metaphase-arrest technique, and the efflux (cell loss by moulting) assessed by counting the number of cells in the corneal layer and recording of intermoult periods. The importance of the methods for assessing these parameters per square unit of skin surface is emphasized. These parameters were studied in eight groups of ten adult male toads sacrificed at various hours of the day. There were minor variations in the cell birth rate, fluctuating around a mean of 26 cells/mm2/hr (obtained at the metaphase collection period from 11.00-14.00 hours). By summation of the cell productions during the eight metaphase collection periods of 3 hr, and extrapolation to an intermoult period (time between two moults), a calculated cell production of about 6340 cells/mm2 in 10.3 days was obtained, whereas the cell loss at each moult was only 2370 cells/mm2. Thus the cell production rate exceeds the rate of cell loss through moults by a factor of 2.7 Arguments are presented that the 'surplus' of cells produced cannot be permanently accommodated within the living epidermis. Consequently a cell deletion rate beyond that by moulting of about 4000 cells/mm2 in 10.3 days or 16 cells/mm2/hr can be calculated. These results are discussed in relation to current concepts of tissue homeostatic mechanism(s). The results are consistent with the hypothesis that controlled cell deletion may be a tissue homeostatic mechanism complementary to controlled cell divisions.

Animals↗