# Molecular basis of brush border assembly

> **NIH NIH R01** · VANDERBILT UNIVERSITY · 2021 · $338,864

## Abstract

SUMMARY
The goal of this renewal application is to define mechanisms that drive the assembly and organization of
enterocyte microvilli: actin bundle-supported membrane protrusions that extend from the apical surface into the
gut lumen and play essential roles in nutrient absorption and barrier function. Numerous intestinal diseases are
linked to the destruction or malformation of microvilli, underscoring the critical physiological importance of
these protrusions. The surface of a single mature enterocyte is populated by hundreds of microvilli, which form
a tightly packed array known as the ‘brush border’. Tight packing maximizes the number of microvilli, the apical
holding capacity for membrane-associated nutrient processing and host defense factors, and thus the
functional capacity of the cell. Although mechanisms of brush border assembly remain poorly understood, our
laboratory has begun to make significant progress on this problem. Groundbreaking studies performed during
the initial funding period led to the discovery of a fundamental mechanism that enterocytes use to organize and
optimize the packing density of microvilli. Briefly, we discovered two brush border-specific protocadherins,
CDHR2 and CDHR5, which form adhesion complexes that physically link the tips of adjacent microvilli on
mature villus enterocytes. In cultured cells lacking these factors, brush border assembly is impaired such that
microvilli are disheveled with significantly reduced packing density. We also identified factors that interact with
the cytoplasmic tails of both protocadherins, including the scaffolds USH1C and ANKS4B, and the actin-based
motor, MYO7B. We refer to the entire five-protein complex as the intermicrovillar adhesion complex (IMAC).
Our published work suggests that USH1C/ANKS4B/MYO7B form a transport module that delivers CDHR2-
dependent adhesion links to the distal tips of microvilli. Preliminary results also show that adhesion links form
between microvilli on the surface of immature cells in the crypt, although they do not yet target to microvillar
tips, suggesting that IMAC transport is activated later, perhaps during the crypt-villus transition. Finally, newly
developed CDHR2 KO mice exhibit striking defects in brush border morphology that have consequences for
enterocyte differentiation and function. In light of these findings, we propose our central hypothesis: USH1C
induces clustering of MYO7B motors, which activates transport of CDHR2-dependent adhesion links to
microvillar tips and drives functional maturation of the brush border as cells exit the crypt. To test this model,
we will use state-of-the-art super-resolution microscopy, new forms of electron microscopy, structural biology,
and assays of epithelial function to: (Aim 1) determine how IMAC formation and localization at microvillar tips
contribute to BB assembly and enterocyte function in vivo, (Aim 2) dissect mechanisms that regulate MYO7B-
driven IMAC transport to microvillar tips, and...

## Key facts

- **NIH application ID:** 10104474
- **Project number:** 5R01DK095811-08
- **Recipient organization:** VANDERBILT UNIVERSITY
- **Principal Investigator:** MATTHEW J TYSKA
- **Activity code:** R01 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2021
- **Award amount:** $338,864
- **Award type:** 5
- **Project period:** 2013-09-01 → 2023-02-28

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/10104474

## Citation

> US National Institutes of Health, RePORTER application 10104474, Molecular basis of brush border assembly (5R01DK095811-08). Retrieved via AI Analytics 2026-05-22 from https://api.ai-analytics.org/grant/nih/10104474. Licensed CC0.

---

*[NIH grants dataset](/datasets/nih-grants) · CC0 1.0*