Alterations in Morphology of Developing Microvilli Elicited by Cytochalasin B

INTRODUCTION aspects of microvillar morphogenesis . This report describes the cytological events that result from exposure of embryonic intestine to CB in organ culture . The ultrastructure of microvilli comprising the brush border of cells of the intestinal epithelium has been extensively studied (e .g ., Ito, 1965 ; Overton et al ., 1965 ; Brunser and Luft, 1970; Mukherjee and Staehelin, 1971), and the sequence of events that occurs during normal development of these organelles has been described for several species (Overton and Shoup, 1964 ; Overton, 1965 ; van der Starre-van der Molen and dePriester, 1972; and Bonneville and Weinstock, 1970) . Nevertheless, the processes that regulate the morphogenesis of microvilli are, for the most part, still enigmatic . Cytochalasin B (CB) somehow interferes with mechanisms that regulate morphogenetic processes in a variety of developing systems (Wessells, et al ., 1971 ; Spooner and Wessells, 1972 ; Wrenn, 1971 ; Yamada et al ., 1971 ; Schroeder, 1969, 1970 ; Cloney, 1969, 1972) . During the course of a study of the effects of CB on morphogenetic folding of the intestinal epithelium in the chick embryo, we discovered that the drug exerted a profound and unusual effect upon the formation of microvilli at the cell surface . CB therefore suggests itself as a potentially useful tool with which to analyze some