# The dynamics and underlying mechanisms controlling cell size and canonical Wnt signaling

> **NIH NIH R35** · HARVARD MEDICAL SCHOOL · 2024 · $749,190

## Abstract

Project Summary/ Abstract
Some of the most challenging problems in biology and disease concern dynamical features of the
cell. The Wnt pathway is one of the most important developmental and cancer pathways.
Control of growth and size is a universal property of all cells, whose dynamics are hard to
measure accurately and poorly understood. The Wnt pathway is made up of conserved scaffolds
and enzymes that control the stability of catenin, which regulates important developmental
genes. Cell growth control, responds to metabolism and differentiation in complex physiological
circuits. Components of the Wnt pathway have been long known but how the Wnt signal
traverses several kinetic steps before interacting with the catenin is still unclear. We are trying
to understand the Wnt pathway from: 1) single molecule imaging of fluorescent chimeric
proteins knocked into the endogenous loci, thereby preserving the exact level of expression and
transcriptional regulation and 2) the development of an in vitro system that preserves the
kinetic response of the downstream events of the pathway. From the in vitro system we can
assay purified proteins, and assess their activity. We can quickly isolate complexes and study
their posttranslational state, and potentially determine the structure of kinetically important
forms by Cryo-electron microscopy. We have in the past and will in the future combine
mathematical modeling with biochemistry to identify key features of this system. For cell size
control we have used quantitative methods to define the cell’s structural and physiological state.
We found that mammalian cell size is controlled, not just at G1/S, but throughout the cell cycle
by feedback from cell size onto growth rate. How cells know how large they are and regulate
their growth is still a mystery. Further understanding will be facilitated by two tools we
developed: computer enhanced Quantitative Phase microscopy (ceQPM) and Normalized
Raman Imaging (NoRI). The former is the most accurate method for measuring cell dry mass
for attached cells. The latter can also independently measure protein and lipid mass densities
and total mass of cells, even deep within tissues. Furthermore, NoRI can measure the rate of
protein synthesis and degradation at the single cell level within tissues or in culture in real time.
We will use ceQPM and NoRI simultaneously with cultured cells to measure protein synthesis
and turnover as a function of cell size and as a function of position in the cell cycle, coupled with
pharmacological, growth factor, and nutrient perturbation to identify pathways involved in
sensing size and regulating growth. The mechanism of cell size control in differentiated organs
under different nutritional states in mouse tissues will also be explored with NoRI.

## Key facts

- **NIH application ID:** 10878827
- **Project number:** 5R35GM145248-03
- **Recipient organization:** HARVARD MEDICAL SCHOOL
- **Principal Investigator:** MARC Wallace KIRSCHNER
- **Activity code:** R35 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2024
- **Award amount:** $749,190
- **Award type:** 5
- **Project period:** 2022-07-22 → 2027-06-30

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/10878827

## Citation

> US National Institutes of Health, RePORTER application 10878827, The dynamics and underlying mechanisms controlling cell size and canonical Wnt signaling (5R35GM145248-03). Retrieved via AI Analytics 2026-05-27 from https://api.ai-analytics.org/grant/nih/10878827. Licensed CC0.

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