RESUMO
Cell size varies greatly between cell types, yet within a specific cell type and growth condition, cell size is narrowly distributed. Why maintenance of a cell-type specific cell size is important remains poorly understood. Here we show that growing budding yeast and primary mammalian cells beyond a certain size impairs gene induction, cell-cycle progression, and cell signaling. These defects are due to the inability of large cells to scale nucleic acid and protein biosynthesis in accordance with cell volume increase, which effectively leads to cytoplasm dilution. We further show that loss of scaling beyond a certain critical size is due to DNA becoming limiting. Based on the observation that senescent cells are large and exhibit many of the phenotypes of large cells, we propose that the range of DNA:cytoplasm ratio that supports optimal cell function is limited and that ratios outside these bounds contribute to aging.
Assuntos
Crescimento Celular , Senescência Celular/fisiologia , Citoplasma/metabolismo , Candida albicans/genética , Candida albicans/crescimento & desenvolvimento , Ciclo Celular , Proliferação de Células , Tamanho Celular , Senescência Celular/genética , Fibroblastos/metabolismo , Células HEK293 , Humanos , Cultura Primária de Células , Saccharomyces cerevisiae/genética , Saccharomyces cerevisiae/crescimento & desenvolvimento , Saccharomycetales/genética , Saccharomycetales/crescimento & desenvolvimento , Saccharomycetales/metabolismo , Transdução de SinaisRESUMO
Animals display substantial inter-species variation in the rate of embryonic development despite a broad conservation of the overall sequence of developmental events. Differences in biochemical reaction rates, including the rates of protein production and degradation, are thought to be responsible for species-specific rates of development1-3. However, the cause of differential biochemical reaction rates between species remains unknown. Here, using pluripotent stem cells, we have established an in vitro system that recapitulates the twofold difference in developmental rate between mouse and human embryos. This system provides a quantitative measure of developmental speed as revealed by the period of the segmentation clock, a molecular oscillator associated with the rhythmic production of vertebral precursors. Using this system, we show that mass-specific metabolic rates scale with the developmental rate and are therefore higher in mouse cells than in human cells. Reducing these metabolic rates by inhibiting the electron transport chain slowed down the segmentation clock by impairing the cellular NAD+/NADH redox balance and, further downstream, lowering the global rate of protein synthesis. Conversely, increasing the NAD+/NADH ratio in human cells by overexpression of the Lactobacillus brevis NADH oxidase LbNOX increased the translation rate and accelerated the segmentation clock. These findings represent a starting point for the manipulation of developmental rate, with multiple translational applications including accelerating the differentiation of human pluripotent stem cells for disease modelling and cell-based therapies.
Assuntos
Embrião de Mamíferos , Desenvolvimento Embrionário , Animais , Humanos , Camundongos , Diferenciação Celular , Desenvolvimento Embrionário/fisiologia , NAD/metabolismo , Oxirredução , Células-Tronco Pluripotentes/citologia , Células-Tronco Pluripotentes/metabolismo , Especificidade da Espécie , Técnicas In Vitro , Transporte de Elétrons , Relógios Biológicos , Fatores de Tempo , Embrião de Mamíferos/citologia , Embrião de Mamíferos/embriologia , Embrião de Mamíferos/metabolismo , Levilactobacillus brevisRESUMO
Cytokinesis is the process where the mother cell's cytoplasm separates into daughter cells. This is driven by an actomyosin contractile ring that produces cortical contractility and drives cleavage furrow ingression, resulting in the formation of a thin intercellular bridge. While cytoskeletal reorganization during cytokinesis has been extensively studied, less is known about the spatiotemporal dynamics of the plasma membrane. Here, we image and model plasma membrane lipid and protein dynamics on the cell surface during leukemia cell cytokinesis. We reveal an extensive accumulation and folding of the plasma membrane at the cleavage furrow and the intercellular bridge, accompanied by a depletion and unfolding of the plasma membrane at the cell poles. These membrane dynamics are caused by two actomyosin-driven biophysical mechanisms: the radial constriction of the cleavage furrow causes local compression of the apparent cell surface area and accumulation of the plasma membrane at the furrow, while actomyosin cortical flows drag the plasma membrane toward the cell division plane as the furrow ingresses. The magnitude of these effects depends on the plasma membrane fluidity, cortex adhesion, and cortical contractility. Overall, our work reveals cell-intrinsic mechanical regulation of plasma membrane accumulation at the cleavage furrow that is likely to generate localized differences in membrane tension across the cytokinetic cell. This may locally alter endocytosis, exocytosis, and mechanotransduction, while also serving as a self-protecting mechanism against cytokinesis failures that arise from high membrane tension at the intercellular bridge.
Assuntos
Actomiosina , Membrana Celular , Citocinese , Citocinese/fisiologia , Membrana Celular/metabolismo , Humanos , Actomiosina/metabolismoRESUMO
Interferon-induced transmembrane protein 3 (IFITM3) has previously been identified as an endosomal protein that blocks viral infection1-3. Here we studied clinical cohorts of patients with B cell leukaemia and lymphoma, and identified IFITM3 as a strong predictor of poor outcome. In normal resting B cells, IFITM3 was minimally expressed and mainly localized in endosomes. However, engagement of the B cell receptor (BCR) induced both expression of IFITM3 and phosphorylation of this protein at Tyr20, which resulted in the accumulation of IFITM3 at the cell surface. In B cell leukaemia, oncogenic kinases phosphorylate IFITM3 at Tyr20, which causes constitutive localization of this protein at the plasma membrane. In a mouse model, Ifitm3-/- naive B cells developed in normal numbers; however, the formation of germinal centres and the production of antigen-specific antibodies were compromised. Oncogenes that induce the development of leukaemia and lymphoma did not transform Ifitm3-/- B cells. Conversely, the phosphomimetic IFITM3(Y20E) mutant induced oncogenic PI3K signalling and initiated the transformation of premalignant B cells. Mechanistic experiments revealed that IFITM3 functions as a PIP3 scaffold and central amplifier of PI3K signalling. The amplification of PI3K signals depends on IFITM3 using two lysine residues (Lys83 and Lys104) in its conserved intracellular loop as a scaffold for the accumulation of PIP3. In Ifitm3-/- B cells, lipid rafts were depleted of PIP3, which resulted in the defective expression of over 60 lipid-raft-associated surface receptors, and impaired BCR signalling and cellular adhesion. We conclude that the phosphorylation of IFITM3 that occurs after B cells encounter antigen induces a dynamic switch from antiviral effector functions in endosomes to a PI3K amplification loop at the cell surface. IFITM3-dependent amplification of PI3K signalling, which in part acts downstream of the BCR, is critical for the rapid expansion of B cells with high affinity to antigen. In addition, multiple oncogenes depend on IFITM3 to assemble PIP3-dependent signalling complexes and amplify PI3K signalling for malignant transformation.
Assuntos
Linfócitos B/metabolismo , Proteínas de Membrana/metabolismo , Fosfatidilinositol 3-Quinases/metabolismo , Fosfatos de Fosfatidilinositol/metabolismo , Proteínas de Ligação a RNA/metabolismo , Transdução de Sinais , Animais , Antígenos CD19/metabolismo , Linfócitos B/enzimologia , Linfócitos B/imunologia , Linfócitos B/patologia , Transformação Celular Neoplásica , Feminino , Centro Germinativo/citologia , Centro Germinativo/imunologia , Centro Germinativo/patologia , Humanos , Integrinas/metabolismo , Microdomínios da Membrana/metabolismo , Camundongos , Camundongos Endogâmicos C57BL , Camundongos Endogâmicos NOD , Modelos Moleculares , Fosforilação , Receptores de Antígenos de Linfócitos B/metabolismoRESUMO
Cell size and cell count are adaptively regulated and intimately linked to growth and function. Yet, despite their widespread relevance, the relation between cell size and count has never been formally examined over the whole human body. Here, we compile a comprehensive dataset of cell size and count over all major cell types, with data drawn from >1,500 published sources. We consider the body of a representative male (70 kg), which allows further estimates of a female (60 kg) and 10-y-old child (32 kg). We build a hierarchical interface for the cellular organization of the body, giving easy access to data, methods, and sources (https://humancelltreemap.mis.mpg.de/). In total, we estimate total body counts of ≈36 trillion cells in the male, ≈28 trillion in the female, and ≈17 trillion in the child. These data reveal a surprising inverse relation between cell size and count, implying a trade-off between these variables, such that all cells within a given logarithmic size class contribute an equal fraction to the body's total cellular biomass. We also find that the coefficient of variation is approximately independent of mean cell size, implying the existence of cell-size regulation across cell types. Our data serve to establish a holistic quantitative framework for the cells of the human body, and highlight large-scale patterns in cell biology.
Assuntos
Contagem de Células , Criança , Humanos , Feminino , Masculino , Biomassa , Tamanho Celular , Correlação de DadosRESUMO
Cell size is believed to influence cell growth and metabolism. Consistently, several studies have revealed that large cells have lower mass accumulation rates per unit mass (i.e., growth efficiency) than intermediate-sized cells in the same population. Size-dependent growth is commonly attributed to transport limitations, such as increased diffusion timescales and decreased surface-to-volume ratio. However, separating cell size- and cell cycle-dependent growth is challenging. To address this, we monitored growth efficiency of pseudodiploid mouse lymphocytic leukemia cells during normal proliferation and polyploidization. This was enabled by the development of large-channel suspended microchannel resonators that allow us to monitor buoyant mass of single cells ranging from 40 pg (small pseudodiploid cell) to over 4,000 pg, with a resolution ranging from â¼1% to â¼0.05%. We find that cell growth efficiency increases, plateaus, and then decreases as cell cycle proceeds. This growth behavior repeats with every endomitotic cycle as cells grow into polyploidy. Overall, growth efficiency changes 33% throughout the cell cycle. In contrast, increasing cell mass by over 100-fold during polyploidization did not change growth efficiency, indicating exponential growth. Consistently, growth efficiency remained constant when cell cycle was arrested in G2 Thus, cell cycle is a primary determinant of growth efficiency. As growth remains exponential over large size scales, our work finds no evidence for transport limitations that would decrease growth efficiency.
Assuntos
Técnicas Biossensoriais , Crescimento Celular , Proliferação de Células/genética , Leucemia Linfoide/genética , Animais , Ciclo Celular/genética , Divisão Celular/genética , Linhagem Celular Tumoral , Humanos , Leucemia Linfoide/patologia , Camundongos , Técnicas Analíticas Microfluídicas , PoliploidiaRESUMO
Palbociclib is a CDK4/6 inhibitor approved for metastatic estrogen receptor-positive breast cancer. In addition to G1 cell cycle arrest, palbociclib treatment results in cell senescence, a phenotype that is not readily explained by CDK4/6 inhibition. In order to identify a molecular mechanism responsible for palbociclib-induced senescence, we performed thermal proteome profiling of MCF7 breast cancer cells. In addition to affecting known CDK4/6 targets, palbociclib induces a thermal stabilization of the 20S proteasome, despite not directly binding to it. We further show that palbociclib treatment increases proteasome activity independently of the ubiquitin pathway. This leads to cellular senescence, which can be counteracted by proteasome inhibitors. Palbociclib-induced proteasome activation and senescence is mediated by reduced proteasomal association of ECM29. Loss of ECM29 activates the proteasome, blocks cell proliferation, and induces a senescence-like phenotype. Finally, we find that ECM29 mRNA levels are predictive of relapse-free survival in breast cancer patients treated with endocrine therapy. In conclusion, thermal proteome profiling identifies the proteasome and ECM29 protein as mediators of palbociclib activity in breast cancer cells.
Assuntos
Neoplasias da Mama/enzimologia , Quinase 4 Dependente de Ciclina/antagonistas & inibidores , Quinase 6 Dependente de Ciclina/antagonistas & inibidores , Piperazinas/farmacologia , Complexo de Endopeptidases do Proteassoma/metabolismo , Proteoma/análise , Piridinas/farmacologia , Temperatura , Biomarcadores Tumorais/metabolismo , Neoplasias da Mama/tratamento farmacológico , Neoplasias da Mama/patologia , Proliferação de Células , Senescência Celular , Feminino , Humanos , Recidiva Local de Neoplasia/tratamento farmacológico , Recidiva Local de Neoplasia/enzimologia , Recidiva Local de Neoplasia/patologia , Fenótipo , Prognóstico , Complexo de Endopeptidases do Proteassoma/química , Inibidores de Proteínas Quinases/farmacologia , Taxa de Sobrevida , Ubiquitina/metabolismoRESUMO
The version of this paper originally published online contained an error in the x-axis of Fig. 2c: the LatB concentrations should be 0.4 and 1 µM, but during typesetting, the 1 µM label was incorrectly changed to 0.1 µM. The label is now correct in the print, PDF, and HTML versions of the paper. In addition, in the article's online Supplementary Information, Supplementary Video 2 was a duplicate of Supplementary Video 1. The correct versions of both videos are now available online.
RESUMO
The monitoring of mechanics in a single cell throughout the cell cycle has been hampered by the invasiveness of mechanical measurements. Here we quantify mechanical properties via acoustic scattering of waves from a cell inside a fluid-filled vibrating cantilever with a temporal resolution of < 1 min. Through simulations, experiments with hydrogels and the use of chemically perturbed cells, we show that our readout, the size-normalized acoustic scattering (SNACS), measures stiffness. To demonstrate the noninvasiveness of SNACS over successive cell cycles, we used measurements that resulted in deformations of < 15 nm. The cells maintained constant SNACS throughout interphase but showed dynamic changes during mitosis. Our work provides a basis for understanding how growing cells maintain mechanical integrity, and demonstrates that acoustic scattering can be used to noninvasively probe subtle and transient dynamics.
Assuntos
Acústica , Análise de Célula Única/métodos , Animais , Fenômenos Biomecânicos , Ciclo Celular , Dactinomicina/metabolismo , Camundongos , MicrofluídicaRESUMO
Recent scientific evidence suggests that chronic pain phenotypes are reflected in metabolomic changes. However, problems associated with chronic pain, such as sleep disorders or obesity, may complicate the metabolome pattern. Such a complex phenotype was investigated to identify common metabolomics markers at the interface of persistent pain, sleep, and obesity in 71 men and 122 women undergoing tertiary pain care. They were examined for patterns in d = 97 metabolomic markers that segregated patients with a relatively benign pain phenotype (low and little bothersome pain) from those with more severe clinical symptoms (high pain intensity, more bothersome pain, and co-occurring problems such as sleep disturbance). Two independent lines of data analysis were pursued. First, a data-driven supervised machine learning-based approach was used to identify the most informative metabolic markers for complex phenotype assignment. This pointed primarily at adenosine monophosphate (AMP), asparagine, deoxycytidine, glucuronic acid, and propionylcarnitine, and secondarily at cysteine and nicotinamide adenine dinucleotide (NAD) as informative for assigning patients to clinical pain phenotypes. After this, a hypothesis-driven analysis of metabolic pathways was performed, including sleep and obesity. In both the first and second line of analysis, three metabolic markers (NAD, AMP, and cysteine) were found to be relevant, including metabolic pathway analysis in obesity, associated with changes in amino acid metabolism, and sleep problems, associated with downregulated methionine metabolism. Taken together, present findings provide evidence that metabolomic changes associated with co-occurring problems may play a role in the development of severe pain. Co-occurring problems may influence each other at the metabolomic level. Because the methionine and glutathione metabolic pathways are physiologically linked, sleep problems appear to be associated with the first metabolic pathway, whereas obesity may be associated with the second.
Assuntos
Dor Crônica , Metaboloma , Monofosfato de Adenosina/metabolismo , Biomarcadores/metabolismo , Dor Crônica/genética , Dor Crônica/metabolismo , Cisteína/metabolismo , Feminino , Humanos , Aprendizado de Máquina , Metabolômica/métodos , Metionina/metabolismo , NAD/metabolismo , Obesidade/metabolismo , Fenótipo , Transtornos do Sono-VigíliaRESUMO
BACKGROUND: Fibromyalgia (FM) patients are likely to differ from healthy controls in muscle activity and in reactivity to experimental stress. METHODS: We compared psychophysiological reactivity to cognitive stress between 51 female FM patients aged 18 to 65 years and 31 age- and sex-matched healthy controls. They underwent a 20-minute protocol consisting of three phases of relaxation and two phases of cognitive stress. We recorded surface electromyography normalized to maximum voluntary muscle contraction (%EMG), the percentage of time with no muscle activity (EMG rest time), and subjective pain and stress intensities. We compared group reactivity using linear modelling and adjusted for psychological and life-style factors. RESULTS: The FM patients had a significantly higher mean %EMG (2.2 % vs. 1.0 %, p < 0.001), pain intensity (3.6 vs. 0.2, p < 0.001), and perceived stress (3.5 vs. 1.4, p < 0.001) and lower mean EMG rest time (26.7 % vs. 47.2 %, p < 0.001). In the FM patients, compared with controls, the pain intensity increased more during the second stress phase (0.71, p = 0.028), and the %EMG decreased more during the final relaxation phase (-0.29, p = 0.036). Within the FM patients, higher BMI predicted higher %EMG but lower stress. Leisure time physical activity predicted lower %EMG and stress and higher EMG rest time. Higher perceived stress predicted lower EMG rest time, and higher trait anxiety predicted higher pain and stress overall. CONCLUSIONS: Our results suggest that repeated cognitive stress increases pain intensity in FM patients. FM patients also had higher resting muscle activity, but their muscle activity did not increase with pain. Management of stress and anxiety might help control FM flare-ups. TRIAL REGISTRATION: Retrospectively registered on ClinicalTrials.gov ( NCT03300635 ).
Assuntos
Fibromialgia , Adolescente , Adulto , Idoso , Eletromiografia , Feminino , Fibromialgia/diagnóstico , Fibromialgia/epidemiologia , Humanos , Pessoa de Meia-Idade , Contração Muscular , Músculo Esquelético , Músculos , Medição da Dor , Adulto JovemRESUMO
The maintenance of cell size homeostasis has been studied for years in different cellular systems. With the focus on 'what regulates cell size', the question 'why cell size needs to be maintained' has been largely overlooked. Recent evidence indicates that animal cells exhibit nonlinear cell size dependent growth rates and mitochondrial metabolism, which are maximal in intermediate sized cells within each cell population. Increases in intracellular distances and changes in the relative cell surface area impose biophysical limitations on cells, which can explain why growth and metabolic rates are maximal in a specific cell size range. Consistently, aberrant increases in cell size, for example through polyploidy, are typically disadvantageous to cellular metabolism, fitness and functionality. Accordingly, cellular hypertrophy can potentially predispose to or worsen metabolic diseases. We propose that cell size control may have emerged as a guardian of cellular fitness and metabolic activity.
Assuntos
Homeostase/fisiologia , Animais , Tamanho Celular , Humanos , Hipertrofia/fisiopatologia , Mitocôndrias/metabolismo , Mitocôndrias/fisiologiaRESUMO
Ribosome profiling identifies ribosome positions on translated mRNAs. A prominent feature of published datasets is the near complete absence of ribosomes in 3' untranslated regions (3'UTR) although substantial ribosome density can be observed on non-coding RNAs. Here we perform ribosome profiling in cultured Drosophila and human cells and show that different features of translation are revealed depending on the nuclease and the digestion conditions used. Most importantly, we observe high abundance of ribosome protected fragments in 3'UTRs of thousands of genes without manipulation of translation termination. Affinity purification of ribosomes indicates that the 3'UTR reads originate from ribosome protected fragments. Association of ribosomes with the 3'UTR may be due to ribosome migration through the stop codon or 3'UTR mRNA binding to ribosomes on the coding sequence. This association depends primarily on the relative length of the 3'UTR and may be related to translational regulation or ribosome recycling, for which the efficiency is known to inversely correlate with 3'UTR length. Together our results indicate that ribosome profiling is highly dependent on digestion conditions and that ribosomes commonly associate with the 3'UTR, which may have a role in translational regulation.
Assuntos
Regiões 3' não Traduzidas , Ribossomos/metabolismo , Animais , Linhagem Celular , Drosophila , Humanos , Nuclease do Micrococo , Biossíntese de Proteínas , RNA Mensageiro/química , RNA Mensageiro/metabolismo , Ribonuclease Pancreático , Proteínas Ribossômicas/análise , Subunidades Ribossômicas Menores de Eucariotos/químicaRESUMO
The analgesic and antipyretic compound acetaminophen (paracetamol) is one of the most used drugs worldwide. Acetaminophen overdose is also the most common cause for acute liver toxicity. Here we show that acetaminophen and many structurally related compounds bind quinone reductase 2 (NQO2) in vitro and in live cells, establishing NQO2 as a novel off-target. NQO2 modulates the levels of acetaminophen derived reactive oxygen species, more specifically superoxide anions, in cultured cells. In humans, NQO2 is highly expressed in liver and kidney, the main sites of acetaminophen toxicity. We suggest that NQO2 mediated superoxide production may function as a novel mechanism augmenting acetaminophen toxicity.
Assuntos
Acetaminofen/química , Acetaminofen/metabolismo , Espécies Reativas de Oxigênio/metabolismo , Acetaminofen/efeitos adversos , Células HeLa , Humanos , Técnicas In Vitro , Rim/efeitos dos fármacos , Rim/metabolismo , Fígado/efeitos dos fármacos , Fígado/metabolismo , Quinona Redutases/metabolismoRESUMO
Cytokinesis is the process where the mother cell's cytoplasm separates into daughter cells. This is driven by an actomyosin contractile ring that produces cortical contractility and drives cleavage furrow ingression, resulting in the formation of a thin intercellular bridge. While cytoskeletal reorganization during cytokinesis has been extensively studied, little is known about the spatiotemporal dynamics of the plasma membrane. Here, we image and model plasma membrane lipid and protein dynamics on the cell surface during leukemia cell cytokinesis. We reveal an extensive accumulation and folding of plasma membrane at the cleavage furrow and the intercellular bridge, accompanied by a depletion and unfolding of plasma membrane at the cell poles. These membrane dynamics are caused by two actomyosin-driven biophysical mechanisms: the radial constriction of the cleavage furrow causes local compression of the apparent cell surface area and accumulation of the plasma membrane at the furrow, while actomyosin cortical flows drag the plasma membrane towards the cell division plane as the furrow ingresses. The magnitude of these effects depends on the plasma membrane fluidity, cortex adhesion and cortical contractility. Overall, our work reveals cell intrinsic mechanical regulation of plasma membrane accumulation at the cleavage furrow that is likely to generate localized differences in membrane tension across the cytokinetic cell. This may locally alter endocytosis, exocytosis and mechanotransduction, while also serving as a self-protecting mechanism against cytokinesis failures that arise from high membrane tension at the intercellular bridge.
RESUMO
Eukaryotic phytoplankton, also known as algae, form the basis of marine food webs and drive marine carbon sequestration. Algae must regulate their motility and gravitational sinking to balance access to light at the surface and nutrients in deeper layers. However, the regulation of gravitational sinking remains largely unknown, especially in motile species. Here, we quantify gravitational sinking velocities according to Stokes' law in diverse clades of unicellular marine microalgae to reveal the cell size, density, and nutrient dependency of sinking velocities. We identify a motile algal species, Tetraselmis sp., that sinks faster when starved due to a photosynthesis-driven accumulation of carbohydrates and a loss of intracellular water, both of which increase cell density. Moreover, the regulation of cell sinking velocities is connected to proliferation and can respond to multiple nutrients. Overall, our work elucidates how cell size and density respond to environmental conditions to drive the vertical migration of motile algae.
Assuntos
Tamanho Celular , Nutrientes , Nutrientes/metabolismo , Gravitação , Fitoplâncton/fisiologia , Fitoplâncton/metabolismo , Fotossíntese , Microalgas/metabolismoRESUMO
Cell density, the ratio of cell mass to volume, is an indicator of molecular crowding and therefore a fundamental determinant of cell state and function. However, existing density measurements lack the precision or throughput to quantify subtle differences in cell states, particularly in primary samples. Here we present an approach for measuring the density of 30,000 single cells per hour with a precision of 0.03% (0.0003 g/mL) by integrating fluorescence exclusion microscopy with a suspended microchannel resonator. Applying this approach to human lymphocytes, we discovered that cell density and its variation decrease as cells transition from quiescence to a proliferative state, suggesting that the level of molecular crowding decreases and becomes more regulated upon entry into the cell cycle. Using a pancreatic cancer patient-derived xenograft model, we found that the ex vivo density response of primary tumor cells to drug treatment can predict in vivo tumor growth response. Our method reveals unexpected behavior in molecular crowding during cell state transitions and suggests density as a new biomarker for functional precision medicine.
RESUMO
All cells are subject to geometric constraints, such as surface area-to-volume (SA/V) ratio, that impact cell functions and force biological adaptations. Like the SA/V ratio of a sphere, it is generally assumed that the SA/V ratio of cells decreases as cell size increases. Here, we investigate this in near-spherical mammalian cells using single-cell measurements of cell mass and surface proteins, as well as imaging of plasma membrane morphology. We find that the SA/V ratio remains surprisingly constant as cells grow larger. This observation is largely independent of the cell cycle and the amount of cell growth. Consequently, cell growth results in increased plasma membrane folding, which simplifies cellular design by ensuring sufficient membrane area for cell division, nutrient uptake and deformation at all cell sizes.