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PubMed2003

Different cell size and cell number contribution in two newly established and one ancient body size cline of Drosophila subobscura.

Latitudinal genetic clines in body size occur in many ectotherms including Drosophila species. In the wing of D. melanogaster, these clines are generally based on latitudinal variation in cell number. In contrast, differences in wing area that evolve by thermal selection in the laboratory are in general based on cell size. To investigate possible reasons for the different cellular bases of these two types of evolutionary response, we compared the newly established North and South American wing size clines of Drosophila subobscura. The new clines are based on latitudinal variation in cell area in North America and cell number in South America. The ancestral European cline is also based on latitudinal variation in cell number. The difference in the cellular basis of wing size variation in the American clines, which are roughly the same age, together with the similar cellular basis of the new South American cline and the ancient European one, suggest that the antiquity of a cline does not explain its cellular basis. Furthermore, the results indicate that wing size as a whole, rather than its cellular basis, is under selection. The different cellular bases of different size clines are most likely explained either entirely by chance or by different patterns of genetic variance--or its expression--in founding populations.

Animals↗
PubMed1988

Epidermal tissue homeostasis. III. Effect of hydrocortisone on cell pool size, cell birth rate and cell loss in normal toads and in toads deprived of the pars distalis of the pituitary gland.

It has previously been shown that in toad epidermis the cell birth rate (Kb) exceeds the rate of cell loss through moulting (Kd) and that the 'surplus' of cells seems to be removed in a controlled manner. Assuming that the epidermis is non-expanding, a Kb/Kd ratio greater than 1 indicates that cell deletion additional to desquamation takes place. In normal toads this ratio is 2-3. Following implantation of hydrocortisone pellets into intact toads (release rate, 18 micrograms/g toad/d), the Kb/Kd ratio, over a period of 14 d of hormone treatment, had increased to about 7, due mainly to an increased Kb and to a lesser extent to a decreased Kd. No change in the epidermal cell pool size had taken place. It was previously shown that, following removal of the pars distalis of the pituitary gland, the Kb/Kd ratio decreased with time, due to a decreasing Kb and an increasing Kd, eventually leading to a decreased epidermal cell pool size. In this paper it is shown that, in pars distalisectomized toads with hydrocortisone pellets implanted, the Kb/Kd ratio is restored to control levels by a restoration of the Kb as well as the Kd. The results differ from those of previous studies in which ACTH or adrenocorticosteroids were administered discontinuously (by injection). Thus, by experimental manipulation, different Kb/Kd ratios can be obtained: low (less than 1, pars distalis ablation), medium (2-3, normal toads) and high (7, hydrocortisone implantation). The potentiality of this unique situation in analysing the important question of how the 'surplus' cells are deleted is discussed.

Animals↗
PubMed1984

The relationship between yeast cell size and cell division in Candida albicans.

The mean size and percentage of budded and unbudded cells of Candida albicans grown in batch culture over a wide range of doubling times have been measured. Cell volume decreased with increased doubling time and a nonlinear approach to an asymptotic minimum was observed. When cells were separated by age according to bud scars, each age showed a similar decrease. During each cell division cycle, size increased slowly during both budded and unbudded periods so that each generation was significantly larger than the preceding. There was no difference in size between the parent portion of budded cells and unbudded cells of the same age. Time-lapse photomicroscopy of cells growing on solid medium showed that cells divide asymmetrically with larger parents having a shorter subsequent cycle time than the smaller daughter, although the time utilized for bud formation was similar. When cells were shifted from a medium supporting a low growth rate and small size to a medium supporting a faster growth rate and larger size, both budded and unbudded cells increased significantly in size. As the doubling time increased, both the budded and unbudded portions of parental and daughter cycles increased.

Candida albicans↗
PubMed1985

Epidermal tissue homeostasis. II. Cell pool size, cell birth rate and cell loss in toads deprived of the pars distalis of the pituitary gland.

Following removal of the pars distalis of the pituitary gland in toads, epidermal efflux from the stratum corneum recruitment cell pool (i.e. production of corneal layers) is greatly increased. In this investigation the cell birth rate is studied by means of the metaphase arrest technique, as a function of time after pars distalis ablation. The method allows assessment of the total cell production over 14 days after the operation, to be compared with the total efflux and changes in the epidermal cell pool size. Whereas in intact toads the rate of cell production exceeds that of cell loss by moulting by a factor of 2.7, the 'surplus' of cells neither being used for formation of corneal layers nor permanently accommodated within the living epidermis, a 'balance sheet' of efflux and influx indicates that following pars distalis ablation all cells produced are also used for the (excessive) formation of corneal cell layers. The observations lend further support to the hypothesis that controlled cell deletion is a tissue homeostatic mechanism complementary to controlled cell divisions.

Animals↗
PubMed2002

Why size matters: altering cell size.

Several genes involved in growth control have lately been demonstrated to exhibit more potent effects on cell size than on cell proliferation. Many of these genes direct protein and ribosomal synthesis, highlighting the interdependence between cell size and macromolecular content. The failure to maintain normal cell size when these genes are deregulated suggests that, in certain contexts, cell growth and division are not coupled or coordinated. Several physiological repercussions of altering cell size have been identified.

Animals↗
PubMed1982

Downward regulation of cell size in Paramecium tetraurelia: effects of increased cell size, with or without increased DNA content, on the cell cycle.

Two temperature-sensitive cell-cycle mutants were used to generate abnormally large cells (size estimated by protein content) with either normal or increased DNA contents. The first mutant, cc1, blocks DNA synthesis, but allows cell growth at the restrictive temperature. The cells do not progress through the cell cycle while at the restrictive temperature, but do recover and complete the cell cycle when returned to permissive conditions. The progeny have increased cell size and normal DNA content. Downward regulation of cell size occurs during the ensuing cell cycle at permissive temperature. Two processes are involved. First, the G1 period is reduced or eliminated. As initial cell size increases there is a progressive shortening of the cell cycle to 75% of normal. This limit cell-cycle duration is reached when the initial mass of the cell is equal to or greater than that of normal cells at the time of DNA synthesis initiation (0.25 of a cell cycle). Cells with the limit cell cycle begin macronuclear DNA synthesis immediately after fission. The durations of the S period and fission are normal. Second, the rate of cell growth is unaffected by the increase in cell size, and results in the partitioning of excess cell mass between the daughter cells at the next fission. The second mutant, cc2, blocks cell division, but allows DNA synthesis to occur at a reduced rate so that cells with up to about 140% of the normal initial DNA content and twice the normal cell mass can be produced. The pattern of cell-cycle shortening is the same as in ccl. The rates of growth and both the rate and amount of DNA synthesis are proportional to the initial DNA content. This suggests that the rates of growth and DNA synthesis are limited by the transcriptional activity of the macronucleus in both cc1 and cc2 cells when they begin the cell cycle with experimentally increased cell mass. Increases in both cell size and initial DNA content are required to bring about increases in the rates of growth and DNA accumulation.

Animals↗
PubMed1976

Cell size and mutual cell adhesion. I. Increase in mutual adhesivenes of HeLa cells from density-inhibited suspension cultures by hypotonic treatment.

HeLa cells harvested from density-inhibited or fast growing suspension cultures, were incubated in NaCl solutions of different tonicity. Cell size enlargement produced by hypotonicity is accompanied by an increased sedimentation rate of the density-inhibited cells, whereas no appreciable change is observed in the sedimentation rate of fast growing cells. Hypotonicity also has no effect on the sedimentation rate of density-inhibited cells which previously had been treated with neuraminidase or trypsin. It is shown that the effect of hypotonicity on density-inhibited cells cannot be ascribed to release of cell surface sialic acids during hypotonic incubation. Several arguments are presented which indicate that the changes in sedimentation rate, as measured in the rotating suspension system, are not the direct consequence of the alterations in cell size, but rather must be attributed to differences in intercellular adhesiveness resulting from the size alterations. Analogous changes in intercellular adhesiveness and cell size are shown to occur during growth in isotonic suspension culture. The results can be explained by assuming that changes in cell size affect the intercellular adhesiveness by modifying the extent to which cell surface sialic acids counteract adhesion.

Agglutination Tests↗
PubMed1998

Body size and cell size in Drosophila: the developmental response to temperature.

In Drosophila, like most ectotherms, development at low temperature reduces growth rate but increases final adult size. Cultures were shifted from 25 degrees C to low (16.5 degrees C) or to high (29 degrees C) temperature at regular intervals through larval and pupal stages, and the flies of both sexes showed an increase or decrease, respectively, in the size of thorax, wing and abdominal tergite. Size changes in the wing blade resulted from changes in the size of the epidermal cells (with only a small increase in cell number in males reared at low temperature). The temperature-shifts became less effective as they were made at successively later developmental stages, demonstrating a cumulative effect of temperature on adult size. The thorax and wing develop from the same imaginal disc, with most cell division occurring in larval stages, but they differ in timing of temperature sensitivity, which extends only to pupariation or into the late pupal stage, respectively. Growth of the adult abdomen occurs largely after pupariation but its size is temperature-sensitive through both larval and pupal stages. We discuss growth control in Drosophila and the likely effects of temperature on food assimilation, growth efficiency and allocation of nutrients to the production of different tissues.

Journal Article↗
PubMed1985

Cell size and cell number in tissue growth and development. An old hypothesis reconsidered.

The development of tissues and organs in the post-embryogenic period has commonly been thought to be by two main consecutive processes: the multiplication of cells followed by a growth in their size. The capacity for recovery following growth restriction has been considered to depend on whether restriction occurred during the phase of cell multiplication, in which case catch-up was permanently inhibited; or later, in which case recovery could occur. This model is now no longer valid for a number of reasons, the main one being that the original assumptions about the sequence of developmental processes have been shown to be false. There certainly seems to be an early period of vulnerability during which restriction is not followed by catch-up, but this cannot now be related to the multiplication of cells.

Animals↗
PubMed2006

RNA interference pinpoints regulators of cell size and the cell cycle.

Cell-based genome-wide RNA interference screens are being used to address an increasingly broad spectrum of biological questions. In one recent screen, Drosophila cell cultures treated with double-stranded RNA were analyzed by flow cytometry, providing a wealth of new information and identifying 488 regulators of the cell cycle, cell size, and cell death.

Animals↗
PubMed1997

Joint regulation of cell size and cell number in the wing blade of Drosophila melanogaster.

We used Drosophila melanogaster to test for compensatory control of cell area and cell number in the regulation of total wing area. In two random bred wild-type base stocks collected from different geographic locations we found a negative association between the area and the number of cells in the wing blade. Three replicate lines were selected for increased or decreased wing area, with cell area maintained at the same level as in the three controls. After eight generations of selection, despite a large and highly significant difference in wing area between the large, control and small selection lines, cell area did not differ significantly between them. Rather, the difference in wing area between selection regimes was attributable to differences in cell number. Over the course of selection, the initially significant negative correlation between cell area and cell number in the wing increased, providing evidence for compensatory regulation of cell area and cell number. As a result of the increasingly negative association between the two traits, the variance in wing area declined as selection proceeded. It will be important to discover the mechanisms underlying the compensatory regulation of cell area and cell number.

Animals↗