Thursday, July 3, 2025 7/3/2025

Determining how cell growth triggers cell division in epidermal stem cells

Award Number: R01AR079860
ORGANIZATION: NATIONAL INSTITUTE OF ARTHRITIS & MUSCULOSKELETAL & SKIN DISEASES
OPDIV: NIH
AWARD CLASS: DISCRETIONARY
AWARD ACTIVITY TYPE: SCIENTIFIC/HEALTH RESEARCH (INCLUDES SURVEYS)
PERIOD OF PERFORMANCE START DATE: 07/15/2021
PERIOD OF PERFORMANCE END DATE: 05/31/2026

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Determining how cell growth triggers cell division in epidermal stem cells - PROJECT SUMMARY This proposal aims to determine how cell growth triggers cell division, which is a fundamental question in cell and developmental biology. Its understanding will also greatly impact our knowledge of cancer, where this process is misregulated. It has long been known that cell growth triggers human cell division at the G1/S transition before DNA is replicated. But, although many key regulatory proteins linking cell growth to cell division are known, the molecular mechanisms mammalian cells use to control their size have remained poorly understood and have been based solely on the study of cells growing in culture. My laboratory recently made a breakthrough advance in understanding how growth triggers division. Contrary to expectations that growth would increase Cyclin D-Cdk4,6 activity, we found instead that cell growth dilutes the cell cycle inhibitor Rb to trigger division in cultured cells. Our discovery of the Rb dilution mechanism in cell culture raises three key questions which are the focus of this grant: 1. What is the molecular mechanism regulating Rb’s concentration dynamics that control cell size? 2. What is the function of Rb-based cell size control? 3. Do Rb dilution or other cell size control mechanisms link cell growth to cell division in vivo. We have begun to address the first question and our preliminary data indicate that the mechanism regulating the size-dependence of Rb concentration is translational. To further determine how this molecular mechanism works we will take an approach using reporters to identify the DNA-sequence element responsible and then the corresponding proteins regulating its function. To address the second question, we will take a mass spectrometry-based approach to measure how protein concentrations change with cell size across the proteome. Preliminary data indicate that proteins associated with senescence phenotypes increase in concentration in large cells. This suggests that cell size may be causal for senescence and cell size control functions to avoid this deleterious outcome. To address the final question to definitively test the Rb dilution and alternative models, we will perform a series of in vivo experiments. This is important because recent studies in cell culture have reported conflicting results about how animal cells control their size. To determine how animal cell growth triggers cell division in vivo, we propose to examine the mouse epidermis because it has a large population of proliferating stem cells whose division dynamics can be assayed using live- cell imaging. We will measure changes in keratinocyte cell size in a series of mouse lines in which the Rb family of genes has been conditionally deleted or over-expressed in the mouse epidermis. This will test our central hypothesis that Rb1 is crucial for cell size control in vivo. We will also use mouse genetics to test the alternative hypothesis that the p38 stress activated protein kinase controls cell size. Taken together, successful completion of these aims will have a big impact on understanding how cell growth triggers cell division. This is important because it allows cells to control their size, which is fundamental to cell physiology.


Issue Date FY	Funding FY	Legal Entity Name	Legal Entity Address	Legal Entity City	Legal Entity State	Legal Entity Zip Code	Legal Entity COUNTY	Legal Entity COUNTRY	Assistance Listing	Award Code	Budget Year	Action Date	Action Type	Action Amount

Issue Date FY: 2025 ( Subtotal = $404,576 )
2025	2025	THE LELAND STANFORD JUNIOR UNIVERSITY	450 JANE STANFORD WAY	STANFORD	CA	94305	SANTA CLARA	USA	Arthritis, Musculoskeletal and Skin Diseases Research	000	5	6/3/2025	NON-COMPETING CONTINUATION	$404,576
														Subtotal = $404,576

Issue Date FY: 2024 ( Subtotal = $404,576 )
2024	2024	THE LELAND STANFORD JUNIOR UNIVERSITY	450 JANE STANFORD WAY	STANFORD	CA	94305	SANTA CLARA	USA	Arthritis, Musculoskeletal and Skin Diseases Research	000	4	6/5/2024	NON-COMPETING CONTINUATION	$404,576
														Subtotal = $404,576

Issue Date FY: 2023 ( Subtotal = $417,089 )
2023	2023	THE LELAND STANFORD JUNIOR UNIVERSITY	450 JANE STANFORD WAY	STANFORD	CA	94305	SANTA CLARA	USA	Arthritis, Musculoskeletal and Skin Diseases Research	000	3	5/16/2023	NON-COMPETING CONTINUATION	$417,089
														Subtotal = $417,089

Issue Date FY: 2022 ( Subtotal = $412,919 )
2022	2022	LELAND STANFORD JUNIOR UNIVERSITY, THE	450 JANE STANFORD WAY	STANFORD	CA	94305	SANTA CLARA	USA	Arthritis, Musculoskeletal and Skin Diseases Research	000	2	6/6/2022	NON-COMPETING CONTINUATION	$412,919
														Subtotal = $412,919

Issue Date FY: 2021 ( Subtotal = $425,435 )
2021	2021	LELAND STANFORD JUNIOR UNIVERSITY, THE	450 JANE STANFORD WAY	STANFORD	CA	94305	SANTA CLARA	USA	Arthritis, Musculoskeletal and Skin Diseases Research	000	1	7/9/2021	NEW	$425,435
														Subtotal = $425,435

Grand Total All Awards = $2,064,595

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Determining how cell growth triggers cell division in epidermal stem cells

Award Number: R01AR079860

ORGANIZATION: NATIONAL INSTITUTE OF ARTHRITIS & MUSCULOSKELETAL & SKIN DISEASES

OPDIV: NIH

AWARD CLASS: DISCRETIONARY

AWARD ACTIVITY TYPE: SCIENTIFIC/HEALTH RESEARCH (INCLUDES SURVEYS)

PERIOD OF PERFORMANCE START DATE: 07/15/2021

PERIOD OF PERFORMANCE END DATE: 05/31/2026

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