1. The Importance of Being Big
Jian Zhang, Rolando Del Aguila, Colette Schneider, Brandt L. Schneider 
Journal of Investigative Dermatology Symposium Proceedings 
Volume 10, Issue 2, Pages (November 2005)
DOI: /j x
Copyright © 2005 The Society for Investigative Dermatology, Inc Terms and Conditions

2. Figure 1
The rapid pace of cell size research. A Pub-Med literature search showed that in recent years, the number of publications on cell size continues to increase at a very rapid pace.
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3. Figure 2
Start is equivalent to the restriction point. In Saccharomyces cerevisiae, cell division is clearly asymmetric resulting in a larger mother cell (m) and a smaller daughter cell (d). Observations indicate that smaller daughters require cell growth to a “critical cell size” in order to progress past Start. Start is a point just prior to G1/S-phase boundary equivalent to the restriction point in mammalian cells. Interestingly, whereas by default mother cells are larger than the “critical cell size,” they still have a cell growth requirement for Start. It is not known if this requirement is also governed by cell size.
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4. Figure 3
Cell growth and cell division. (A) In nearly all somatic cells, cell division is dependent upon cell growth. Homeostasis is maintained because on the average, cells double their mass before dividing. (B) In contrast, in some cell types, cell growth and cell division can be uncoupled. For example, neurons, oocytes, and adipocytes can grow without dividing. (C) Cells that are unusually large (e.g., oocytes) can proliferate in absence of cell growth. In this case, normal G1-phase cell cycle controls are absent and cells divide rapidly. Homeostasis is maintained because once cells become smaller than normal, cell division again becomes dependent upon cell growth.
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5. Figure 4
Cln protein levels are is modulated by cell size. A conditional Cln yeast strain BS111 was transformed with a spADH–CLN2–HA construct. In the presence of glucose, this construct is the only source of Cln for this strain. In this case, in contrast to wild-type cells, CLN2 mRNA levels are constitutive and not cell size dependent. In contrast, western analysis of elutriated fractions demonstrates that Cln2 protein levels are size dependent. B-tubulin is used for a loading control. Lanes N and P are negative (e.g., a strain with an untagged CLN2 gene) and positive (e.g., CLN2–HA3 over-expressed from the GAL promoter) controls. (B) Quantitation of the western data and normalization to the B-tubulin loading controls revealed that Cln2 protein abundance was more than 30-fold higher in the large 60 fL cells as compared with the smaller 29 fL cells.
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6. Figure 5
Proliferative capacity correlates with cell size. (A) A wild-type yeast strain where the endogenous CLN1 gene is tagged with an HA epitope was grown for 4 d at room temperature to saturation. Cell fractions of different sizes were collected by centrifugal elutriation and then released into fresh medium and incubated at room temperature. Time and size to Start (50% budded) was determined for six different sized fractions. A near linear relationship between cell size and proliferative capacity was observed indicating that under these conditions cell size determines the probability of cell division. (B) The rate of cell volume increase (fL per h) was plotted for each fraction and found to be cell size dependent for fractions 1–5. (C) The expression of Cln1–HA protein at Start in each fraction was analyzed by the western blot. Initial size, cell size at Start, and time to Start are given. B-tubulin is used for a loading control. Lanes N and P are negative (e.g., a strain with an untagged CLN1 gene) and positive (e.g., CLN1–HA3 over-expressed from the GAL promoter) controls. (D) Quantitation of the western data and normalization to the B-tubulin loading controls revealed that Cln1 protein abundance correlated more closely to growth rate than to cell size.
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7. Figure 6
Cell size mutants. (A) Photomicroscopy of a mixture of wild-type and yeast mutants revealed that it was possible to differentiate large (U) and small (W) cell mutants from wild-type cells (WT). Measurements indicate that the largest mutants are ∼10-fold larger than the smallest. Scale bar∼5 μM. (B) Coulter counter analysis of 5958 single gene deletion mutants. The number of deletion mutants was plotted as a function of their mean size.
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8. Figure 7
The Ccr4–Not transcriptional complex. Analysis of cell size mutants revealed that the Ccr4–Not transcriptional complex appears to be involved in cell size regulation. Deletion of the genes for Hpr1, Paf1, Flr1, Caf1, and Ccr4 (shaded gray) resulted in abnormally large cells. Interestingly, all five of these gene products interact physically in Ccr4–Not transcriptional complexes. Ccr4 is the core component of complexes involved in transcription and poly (A) deadenylation. In addition, four other gene products (shown in italics and underlined) are known to effect cell size, cell cycle progression, or CLN expression.
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9. Figure 8
CLN1 expression in cell size mutants. (A) Deletion of the gene for Rpt2 results in abnormally large cells. Asynchronous cultures were elutriated and synchronized G1-phase cells were followed through a time course. Northern analysis revealed that CLN1 mRNA peaked at 111 fL. Asynchronous cultures (AS) are shown for reference. Blots were probed with ACT1 to control for loading. (B) Deletion of the gene for Sac1 results in abnormally small cells. Asynchronous cultures were elutriated and synchronized G1-phase cells were followed through a time course. Northern analysis revealed that CLN1 mRNA peaked at 50 fL. AS are shown for reference. Blots were probed with ACT1 to control for loading. (C) Expression of relative levels CLN1 normalized to ACT1 in sac1Δ and rpt2Δ mutants is plotted as a function of cell size. Under these conditions, in wild-type cells CLN1 mRNA expression peaks around 65 fL.
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