# Mechanisms of Hepatocyte Polarization and Apical Tube Formation

> **NIH NIH R01** · UNIVERSITY OF PENNSYLVANIA · 2021 · $392,386

## Abstract

Project Summary/Abstract:
The functions of the liver, including detoxification, synthesis of serum proteins, and bile production, critically
depend on hepatocyte polarization and bile canaliculus (BC) formation. Defects in these processes are
associated with serious liver diseases such as cholestasis and hepatocarcinoma. Using the rat hepatocyte
line Can 10, the only known cells that can proliferate and form “tubular” BCs (tBCs) in vitro that resembles
those in vivo, we discovered that hepatocyte polarization and “primordial” BC formation are linked to
cytokinesis. This division-linked mechanism also applies to BC biogenesis during liver development.
However, it remains a mystery how a primordial BC formed between two daughter cells at the division site is
remodeled and grown into a tBC nestled between two rows of cells, as seen in the liver.
We hypothesize that tBC formation involves spatiotemporal coordination of oriented divisions, with BC
expansion driven by targeted exocytosis, elongation by pushing forces from both sides of the BC, and
extension along the cell-cell contact through constant remodeling of the adherens and tight junctions. To
identify the steps and key players involved, we employed two non-biased approaches. The first involves
identification of genes from single-cell transcriptomic analysis of liver development that are induced or
increased at stages of hepatocyte polarization and BC formation. The second involves identification of
genes whose expressions are increased in the polarized Can 10 cells versus the unpolarized parental cells.
These complementary approaches have led to the discovery of numerous genes that may play an important
role in a process from the terminal stage of cytokinesis to tBC formation. 11 candidate genes were selected
for a small siRNA-based screen, three (KIF21B, ABLIM3, and IPCEF1) were found to be required for tBC
formation. None of these has been implicated previously in epithelial tube formation. In this application, we
will use an interdisciplinary approach to test our hypotheses that the microtubule (MT) plus end-directed
motor Kif21B and the actin-binding protein Ablim3 act in concert to drive BC expansion by controlling MT-
and actin-mediated vesicle transport as well as adherens junction (AJ) assembly (Aim 1), and that the
scaffold protein Ipcef1 promotes Arf6 activation by distinct cytohesins (GEFs) at distinct locations to control
AJ remodeling, apical vesicle recycling, and actin-based protrusions to drive BC elongation (Aim 2). As the
mechanisms of apical tube formation are highly conserved from worms to humans, the impact of our
proposed study will likely reach far beyond the field of liver biology.

## Key facts

- **NIH application ID:** 10221385
- **Project number:** 1R01DK128861-01
- **Recipient organization:** UNIVERSITY OF PENNSYLVANIA
- **Principal Investigator:** Erfei Bi
- **Activity code:** R01 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2021
- **Award amount:** $392,386
- **Award type:** 1
- **Project period:** 2021-07-01 → 2025-03-31

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/10221385

## Citation

> US National Institutes of Health, RePORTER application 10221385, Mechanisms of Hepatocyte Polarization and Apical Tube Formation (1R01DK128861-01). Retrieved via AI Analytics 2026-05-25 from https://api.ai-analytics.org/grant/nih/10221385. Licensed CC0.

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