# Adherens junctions limit septate junction length in Drosophila midgut enterocytes but are not required for polarity

## TL;DR

In fruit fly midgut cells, cadherin proteins aren't needed for cell polarity but help control the size of junctions between cells.

## Contribution

Shows that cadherins are not essential for polarity in Drosophila midgut, but are crucial for limiting septate junction size.

## Key findings

- Loss of E-cadherin, Armadillo, or α-catenin does not affect midgut polarity or organization.
- E-cadherin and armadillo mutants show expanded septate junctions and shorter lateral domains.
- Cadherin-mediated adhesion is not required for polarity but defines septate junction size and cell height.

## Abstract

Adherens junctions formed by E-cadherin adhesion complexes play central roles in the organisation and apical-basal polarisation of both mammalian and insect epithelia. Here, we investigate the function of the components of the E-cadherin adhesion complex in the Drosophila midgut epithelium, which establishes polarity by a different mechanism from other fly epithelia and has an inverted junctional arrangement in which the adherens junctions lie below the septate junctions. Unlike other epithelial tissues, loss of E-cadherin, Armadillo (β-catenin) or α-catenin has no effect on the polarity or organisation of the adult midgut epithelium. This is not due to redundancy with other cadherins, as enterocytes lacking E-cadherin, N-cadherin and CadN2 still polarise normally. However, E-cadherin (shg) and armadillo mutants have expanded septate junction domains and shorter lateral domains below the septate junctions, indicating that E-cadherin adhesion complexes limit the basal extent of the septate junctions. Thus, Cadherin-mediated adhesion is dispensable for apical-basal polarity and epithelial organisation in the Drosophila midgut, in contrast to all other epithelia that have been studied so far, but it is required to define the size of the septate junctions and cell height.

Highlighted Article:
Drosophila midgut epithelium does not require Cadherins for polarity in the midgut, but these proteins are required to limit the extent of the septate junctions.