The cellular mechanism of epithelial rearrangement during morphogenesis ofthe Caenorhabditis elegans dorsal hypodermis

The mechanism by which epithelial cells rearrange is a process that is cent ral to epithelial morphogenesis, yet remains poorly understood. We have inv estigated epithelial cell rearrangement in the dorsal hypodermis of the Cae norhabditis elegans embryo, in which two rows of epithelial cells rearrange in a morphogenetic process known as dorsal intercalation. The intercalatin g cells extend basal protrusions which squeeze between their opposing neigh bors beneath their adherens junctions. As the intercalating cells move forw ard, these protruding tips become broader in the anterior-posterior and dor soventral dimensions, effectively "plowing through" the adherens junctions and forcing an opening for the remainder of the intercalating cell to inser t between the contralateral cells. These cell movements are dependent upon intact cytoarchitecture, since the pharmacological disruption of microtubul es or actin filaments blocks cell rearrangement. The cells appear to interc alate independently of immediately adjacent neighboring hypodermal cells be cause dorsal intercalation is not blocked by the ablation of the progenitor s for either half of the lateral hypodermal cells or the posterior half of the dorsal hypodermis. This is the first case in which the protrusive mecha nism underlying epithelial cell rearrangement has been characterized, and w e propose a model describing how epithelial cells rearrange within the conf ines of an epithelial monolayer, and discuss the mechanisms that may be gui ding these directed cell movements. (C) 1998 Academic Press.