How genes encode the three-dimensional shape of tissues is a fascinating problem in biology. Pioneering genetic studies in the fruit fly Drosophila have identified key genes that control the generation of force patterns in the developing wing. Shortrange force patterns generated by planar polarised myosins can promote boundary formation and tissue elongation during the larval wing disc stage. Long-range force patterns are also crucial to shaping the wing during the pupal stage. We review the different ways in which both local and global force patterns can be generated, such as: patterned acto-myosin contractility, patterned anchorage to the extracellular matrix, and patterned tissue growth. In all cases, the balance between force, mass, and resistance explains how the resulting mechanical response produces particular tissue forms-a point underscored by the ability of computer simulations of tissue mechanics to reproduce such morphogenetic events.

SummaryBasement membranes (BMs) are specialized extracellular matrices required for tissue organization and organ formation. We study the role of laminin and its integrin receptor in the regulation of tissue migration during Drosophila oogenesis. Egg production in Drosophila involves the collective migration of follicle cells (FCs) over the BM to shape the mature egg. We show that laminin content in the BM increases with time, whereas integrin amounts in FCs do not vary significantly. Manipulation of integrin and laminin levels reveals that a dynamic balance of integrin-laminin amounts determines the onset and speed of FC migration. Thus, the interplay of ligand-receptor levels regulates tissue migration in vivo. Laminin depletion also affects the ultrastructure and biophysical properties of the BM and results in anterior-posterior misorientation of developing follicles. Laminin emerges as a key player in the regulation of collective cell migration, tissue stiffness, and the organization of anterior-posterior polarity in Drosophila.