Effects of cytochalasin B on the formation of previllous ridges and the appearance of long microvillous-like processes in the organ culture system of chick embryonic intestine.

Between 8 and 12 days of incubation the embryonic duodenum serially constructs with relative regularity the previllous ridges upon which the definitive villi later form. The effects of cytochalasin B (CB) on the formation of these previllous ridges of the duodena of developing chick embryos were studied, varying the concentrations and exposure time of CB in the organ culture system. The results were as follows: CB inhibited the formation of new previllous ridges from the epithelial cell sheets of 8- to 11-day-old embryonic duodena at cultured time of 24h. CB treatment blocked or delayed cytokinesis of the epithelial cells and the production of many long microvillous-like processes (long processes) from the surface of the epithelial cells. These long processes elicited by CB contained actin filaments and their appearance was influenced by the developmental stages of embryos and local parts of epithelial cells. With 11-day embryonic duodena, induction of long processes by CB was observed at various concentrations (1 microgram/ml-16 micrograms/ml) and even after short exposure of 15 min. Cytochalasin D (CD) and colchicine were used and long processes were induced by CD but not by colchicine itself. The appearance of long processes depended on the experimental concentration of CB, CD and colchicine. In normal developments, such long processes appeared and disappeared within a confined area during the formation of previllous ridges (Noda, 1981). This study seemed to provide experimental support for the previous reported suggestion that the long processes might be one of the important factors in the formation of the previllous ridges of chick embryonic duodena.