Abstract
Planar polarity refers to cellular polarity in an orthogonal plane to apicobasal polarity, and is seen across scales from molecular distributions of proteins to tissue patterning. In many contexts it is regulated by the evolutionarily conserved ‘core' planar polarity pathway that is essential for normal organismal development. Core planar polarity pathway components form asymmetric intercellular complexes that communicate polarity between neighbouring cells and direct polarised cell behaviours and the formation of polarised structures. The core planar polarity pathway consists of six structurally different proteins. In the fruitfly Drosophila melanogaster, where the pathway is best characterised, an intercellular homodimer of the seven-pass transmembrane protein Flamingo interacts on one side of the cell junction with the seven-pass transmembrane protein Frizzled, and on the other side with the four-pass transmembrane protein Strabismus. The cytoplasmic proteins Diego and Dishevelled are co-localised with Frizzled, and Prickle co-localises with Strabismus. Between these six components there are myriad possible molecular interactions, which could stabilise or destabilise the intercellular complexes and lead to their sorting into polarised distributions within cells. Post-translational modifications are key regulators of molecular interactions between proteins. Several post-translational modifications of core proteins have been reported to be of functional significance, in particular phosphorylation and ubiquitination. In this review, we discuss the molecular control of planar polarity and the molecular ecology of the core planar polarity intercellular complexes. Furthermore, we highlight the importance of understanding the spatial control of post-translational modifications in the establishment of planar polarity.
Highlights
Many cells require asymmetrical architecture — termed polarity — that allows structures to be compartmentalised within a cell in order to fulfil their function
Apicobasal polarity is common in many cell types such as neurons, where it enables unidirectional signal transduction, and epithelial cells, enabling unidirectional secretion
Cells can be polarised in an orthogonal plane, which is termed planar polarity, known as planar cell polarity (PCP)
Summary
Many cells require asymmetrical architecture — termed polarity — that allows structures to be compartmentalised within a cell in order to fulfil their function. Part 1 of 2 (A) Schematic of localisation of core planar polarity pathway protein complexes in cells of the Drosophila pupal wing. This shows that Dsh activity is required for planar polarisation of core pathway components such as Fmi and Stbm.
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