# In vivo polarity establishment and symmetry breaking in an epithelial tissue

> **NIH NIH F32** · STANFORD UNIVERSITY · 2020 · $65,310

## Abstract

SUMMARY
Epithelial cells have essential functions in tissue integrity and selective molecular transport. which depend
upon the differential targeting of proteins to plasma membranes during polarity establishment and
maintenance. Loss of epithelial polarity is associated with serious, life threatening diseases including the
progression of cancers, polycystic kidney disease, and cystic fibrosis. Despite the importance of polarity,
surprisingly little is known about the mechanisms that direct apical and basolateral proteins to the correct
surfaces, and almost nothing is known about how cells break symmetry to establish polarity during in vivo
organogenesis. Recent advances in genomic editing, tissue specific protein depletion, and live imaging make
these questions approachable at a previously unattainable level. In the simple epithelium of the embryonic C.
elegans intestine, PAR-3 (and other apical polarity proteins) move from puncta on lateral membranes to the
future apical surface in a microtubule-dependent manner. Depletion of microtubules delays but does not
abolish polarity establishment, suggesting other parallel pathways are involved in polarization, which may
include actomyosin and/or membrane trafficking based on in vitro studies and parallel roles for these pathways
in other contexts. Consistent with this hypothesis, my preliminary data show that basolateral polarity proteins
initially move to the future apical surface by a different route than apical proteins, before being retargeted to
basolateral membranes. Additionally, my preliminary data implicate membrane trafficking in polarity
establishment as RNAi depletion of secretory proteins (SEC-23 or SNAP-29) abrogates apical polarity. Thus, I
will test the hypothesis that parallel pathways involving microtubules, actin, and/or membrane
trafficking are required to break symmetry and establish apical-basolateral polarity in the intestinal
epithelium. In Specific Aim 1, I will determine the mechanisms by which proteins move to apical versus
basolateral plasma membranes, using live imaging of fluorescently tagged endogenous proteins to define their
relative movements during polarization. I will test the roles of the cytoskeleton in polarity establishment by live
imaging embryos after chemically or genetically perturbing the cytoskeleton. A forward genetic screen in a
sensitized background lacking microtubules will identify additional parallel pathways involved in polarity
establishment. In Specific Aim 2, I will determine the requirement for membrane trafficking in polarity
establishment by depleting SEC-23 or SNAP-29 specifically within the intestine. Chemical and RNAi screens
will identify additional membrane trafficking proteins involved in polarity establishment, which will be validated
with tissue specific depletion. Site directed mutagenesis will determine the sequences required for the targeting
of basolateral proteins. In vivo and ex vivo manipulation of intestinal geometry will determ...

## Key facts

- **NIH application ID:** 9840391
- **Project number:** 5F32GM129900-02
- **Recipient organization:** STANFORD UNIVERSITY
- **Principal Investigator:** Melissa Anne Pickett
- **Activity code:** F32 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2020
- **Award amount:** $65,310
- **Award type:** 5
- **Project period:** 2019-02-01 → 2021-01-31

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/9840391

## Citation

> US National Institutes of Health, RePORTER application 9840391, In vivo polarity establishment and symmetry breaking in an epithelial tissue (5F32GM129900-02). Retrieved via AI Analytics 2026-05-23 from https://api.ai-analytics.org/grant/nih/9840391. Licensed CC0.

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