The role of contractile microfilaments in the morphogenesis of the developing foregut of chick embryos

摘要

The cellular processes that lead to changes in shape (morphogenesis) and organ formation (organogenesis) are poorly understood. Local contraction of microfilaments can change cell shape and lead to changes of tissue shape. To clarify the role of contactile microfilaments in the foregut morphogenesis of chick embryos, 2- to 4-day-old embryos were exposed to cytochalasin D (CD), which is known to disrupt microfilaments. Untreated age-matched embryos were used as controls. Sections of treated embryos and controls were stained with phalloidin, which binds to actin, and examined with a fluorescence microscope. Microdissected specimens were examined using a scanning electron microscope (SEM). Immunofluorescent staining showed a bright signal belt toward the apical cell region of the foregut epithelium in controls. This signal was not evident in CD-exposed embryos. SEM micrographs of the controls showed the cranial foregut as a smooth, even, cylindrical structure in all stages studied. The lumen was narrow and perfectly straight, the ventral and dorsal walls were in close apposition. The foregut of CD-exposed specimens, however, showed a wide lumen and the walls were separated from each other. The structure seemed atonic and appeared conical, curved, or tilted. We observed a dense microfilament network toward the apical cell pole of the epithelial foregut cells of controls that was no longer evident after CD exposure. This network seems to play an important role in foregut morphogenesis, since actin-filament disruption by CD causes loss of the normal shape.