GROWTH PRESSURE CAN DRIVE EARLY CHICK LENS GEOMETRIES

Over a number of morphological stages during chick lens morphogenesis, a flat plate of cuboidal ectodermal cells infolds to form a deep cup of tall, pyramidal lenticular cells. This invagination process is acco mpanied by asynchronous cellular multiplication over a basal region co nstrained by an adhesive extracellular matrix. A lens placode is forme d as the cells crowd into columnar ''palisades.'' A lens cup forms as the cells pyramidalize owing to basal nuclear movements. Invagination ends when the opening into the lens cup is closed to form a lens vesic le. In this paper, equations are developed that provide a quantitative , mathematical formulation of an earlier theory that explains this inv agination as a growth driven process. The equations take into account the lens cell cycle, the extracellular matrix, and nuclear migratory b ehaviors. Based on the equations, geometries simulating the morphologi cal stages and the cell cycle phases are generated for the lst day of lens development. The mathematical formulation of lens invagination he lps demonstrate how growth pressure alone can be the primary driving f orce for tissue folding. In this view, recruitment occurs before the s hape changes; and cell-autonomous mechanisms of invagination, involvin g the cytoskeleton or differential adhesion alone, offer inadequate ex planations of these changes. (C) 1993 Wiley-Liss, Inc.