A Catalogue of Processes Responsible for Metazoan Morphogenesis

Abstract

Morphogenesis results from factors and control processes present in eggs or ones that arise during development. Individual cells migrate, elongate, narrow, divide at controlled rates, grow, secrete materials, or die, as they participate in morphogenesis. Groups of cells are coordinated in these behaviors so that the population changes in shape. This coordination may result from residence in cohesive epithelial populations, from being subjected to local systemic factors such as mechanical tensions or regulatory agents, or from coincident activation of internal machinery or processes. Morphogenesis is based on a relatively small number of a) cellular structures and functions (cytoskeleton, surface, mitotic controls, synthetic and secretory machinery); b) extracellular materials (basal lamina, extracellular matrix materials such as collagen, fibronectin, hyaluronate, cerebrospinal fluid); and c) systemic properties (tensions, pressures, mass effects). All of these are potential sites where genetic and developmental alterations could yield the changes in body form and function seen in both the microevolutionary and macroevolutionary histories of animals.