Cultured midgut cells of Heliothis virescens (Lepidoptera): fibronectin and integrin beta(1) immunoreactivity during differentiation in vitro

The midgut epithelium of larval Lepidoptera consists of a monolayer of matu re columnar and goblet cells in vivo with loosely bound stem cells at its b ase. Cultures of Heliothis virescens midgut contained quiescent and dividin g stem cells, differentiating and mature cells as well as small rows of att ached cells, randomly distributed in the culture vessel. Fixed cultures wer e immunostained with polyclonal antibodies to fibronectin and integrin beta (1). Many stem cells stained darkly; lighter staining stem cells imply that some stem cells can become less adhesive. Developing cells were pale, lack ing integrin and fibronectin epitopes on their surfaces, and were probably poorly adhesive. During a molt in vivo, differentiating stem cells insert b etween existing epithelial cells, increasing gut size; lack of stickiness w ould enable them to do so. As pre-columnar cells differentiated in vitro, s tainability reappeared. Mature columnar cells were decorated with a pattern of intense surface immunostaining material. Small immature columnar and go blet cells adhered to the distal ends of mature columnar cells by their pro ximal areas near a fibronectin positive area. Goblet cells, seldom found to gether in vivo or in vitro, lacked prominent fibronectin or integrin-like s urface proteins. Cells were joined to each other in the same orientation an d cell pattern observed in intact midguts. The pattern was achieved in vitr o by cell-cell adhesion without basal membrane or existing midgut as guides .