Abstract
How biochemical and mechanical information are integrated during tissue development is a central question in morphogenesis. In many biological systems, the PIX-GIT complex localises to focal adhesions and integrates both physical and chemical information. We used Drosophila melanogaster egg chamber formation to study the function of PIX and GIT orthologues (dPix and Git, respectively), and discovered a central role for this complex in controlling myosin activity and epithelial monolayering. We found that Git’s focal adhesion targeting domain mediates basal localisation of this complex to filament structures and the leading edge of migrating cells. In the absence of dpix and git, tissue disruption is driven by contractile forces, as reduction of myosin activators restores egg production and morphology. Further, dpix and git mutant eggs closely phenocopy defects previously reported in pak mutant epithelia. Together, these results indicate that the dPix-Git complex controls egg chamber morphogenesis by controlling myosin contractility and Pak kinase downstream of focal adhesions.
Highlights
Organogenesis requires the coordinated integration of biochemical and mechanical information at the level of cells and their neighbours, as well as across entire tissues [1,2]
To further understand the role of the dPix-Git signalling module in organogenesis, we examined dpix and git mutant D. melanogaster and focused on defects that were common to both mutations. dpix and git were each required during egg chamber development for cell intercalation, correct myosin activation, and to maintain a follicular epithelial monolayer
To test if dpix and git function redundantly in egg chamber development we generated dpix, git double mutant animals. These animals were semi-viable and eclosed with crumpled wings (S1A Fig), but produced no mature eggs (Fig 1C). This indicates that the dPix-Git signalling complex is essential for egg development, and the more severe phenotype in double mutants compared to each single mutant suggests that dpix and git have partially independent roles
Summary
Organogenesis requires the coordinated integration of biochemical and mechanical information at the level of cells and their neighbours, as well as across entire tissues [1,2]. Over a period of days the egg chamber grows by approximately three orders of magnitude This growth is preferentially channeled along the egg chamber’s anterior-posterior axis to form a 2–3 fold elongated ellipsoid of approximately 850 cells, which establishes the foundations of the embryonic body plan. During this period of growth and elongation the somatic follicle cells maintain apical-basal polarity [6] and tissue monolayering to preserve egg chamber function and integrity [7,8,9]
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