How diverse cells position themselves in an embryo: Variations on a common cytoskeletal theme

Understanding morphogenesis, the spatial and temporal distribution of cells during development of an organism, is a key goal in studies in developmental biology. Throughout diverse developmental systems, only a few cytoskeletal mechanisms are used to achieve the cell shape changes and movements that are required for development to proceed properly. Among these mechanisms is apical constriction, the active narrowing of the apical side of a cell to drive its movement. This mechanism is critical during development of C. elegans , sea urchins, Drosophila, and Xenopus, including neural tube closure in vertebrates. The organisms use a variety of patterning mechanisms to spatially regulate this common cytoskeletal movement. We have found that apical constriction is used reiteratively in cells of distinct lineages to internalize during gastrulation in C. elegans. This presents an opportunity to examine the diversity of patterning mechanisms that regulate cell movements within a single organism. Our results show that these cells in distinct lineages use different fate regulators and surprisingly different cell polarity regulators to control the timing of internalization during gastrulation. We conclude that while diverse organisms utilize diverse patterning mechanisms to regulate common cytoskeletal mechanisms for cell internalization, diverse patterning mechanisms can be associated with common cytoskeletal mechanisms within a single organism.