The WIRS motifs in Fat2 are required for Drosophila egg chamber rotation but not for elongation.

The elongation of tissues and organs is important for proper morphogenesis in animal development. In Drosophila ovaries, the elongation of egg chambers involves aligned Collagen IV fiber-like structures, a gradient of extracellular matrix stiffness and actin-based protrusion-driven collective cell migration, leading to the rotation of the egg chamber. Egg chamber elongation and rotation depend on the atypical cadherin Fat2. Fat2 contains in its intracellular region three WRC interacting receptor sequence (WIRS) motifs, which previously had been shown to bind to the WAVE regulatory complex (WRC), a conserved actin regulator. Here, we show that in fat2 mutant flies lacking the WIRS motifs, egg chambers fail to rotate and Collagen IV fiber-like structures are impaired, yet a gradient of extracellular matrix stiffness is established and egg chambers properly elongate. We conclude that the WIRS motifs are required for egg chamber rotation and that egg chamber rotation might be a prerequisite for proper formation of Collagen IV fiber-like structures. Egg chamber rotation, however, is dispensable for extracellular matrix stiffness gradient formation and for egg chamber elongation.