Sculpting epithelia with planar polarized actomyosin networks: Principles from Drosophila

Drosophila research has revealed how planar polarized actomyosin networks affect various types of tissue morphogenesis. The networks are positioned by both tissue-wide patterning factors (including Even-skipped, Runt, Engrailed, Invected, Hedgehog, Notch, Wingless, Epidermal Growth Factor, Jun N-terminal kinase, Sex combs reduced and Fork head) and local receptor complexes (including Echinoid, Crumbs and Toll receptors). Networks with differing super-structure and contractile output have been discovered. Their contractility can affect individual cells or can be coordinated across groups of cells, and such contractility can drive or resist physical change. For what seem to be simple tissue changes, multiple types of actomyosin networks can contribute, acting together as contractile elements or braces within the developing structure. This review discusses the positioning and effects of planar polarized actomyosin networks for a number of developmental events in Drosophila, including germband extension, dorsal closure, head involution, tracheal pit formation, salivary gland development, imaginal disc boundary formation, and tissue rotation of the male genitalia and the egg chamber.