Burgess D R
J Embryol Exp Morphol. 1975 Dec;34(3):723-40.
Villi lining the avian intestine originate from longitudinal folds (previllous ridges) running the length of the embryonic intestine. The morphogenetic events that occur in the epithelium during initial ridge formation in the chick embryo duodenum were examined by light and electron microscopy. The epithelium, in cross-section, undergoes three stages prior to the formation of ridges; termed the circle (4 1/2-6 days), the ellipse (6-8 1/2 days), and the triangle (5 1/2-9 days). At about 9 days of development three ridges form with three more forming one day later. The mechanisms responsible for folding of the epithelium were examined. Microdissection followed by organ culture demonstrated that constriction by the surrounding circular smooth muscle cannot account for folding of the epithelium. Mitotic pressure within the epithelium also cannot account for folding since there is no difference in the number of epithelial cells per cross-section between the ellipse and the triangle stages and the epithelial tube is not restricted from expanding. Active constrictions in groups of epithelial cells, mediated by bands of microfilaments, are thought to cause folding. Bundles of microfilaments are localized in the apical region of all epithelial cells at all stages studied and are localized in the basal region of those cells occupying the crests of the forming ridges. Cytochalasin B-treatment prevented ridge formation and disrupted the bundles of microfilaments.
鸟类肠道内的绒毛起源于沿胚胎肠道全长分布的纵向褶皱（绒毛前嵴）。利用光学显微镜和电子显微镜，研究了鸡胚十二指肠初始嵴形成过程中上皮细胞发生的形态发生事件。在横切面上，上皮细胞在嵴形成之前经历三个阶段，分别称为圆形期（4.5 - 6天）、椭圆形期（6 - 8.5天）和三角形期（5.5 - 9天）。在发育约9天时形成三条嵴，一天后又形成另外三条嵴。研究了上皮细胞折叠的机制。显微解剖后进行器官培养表明，周围环形平滑肌的收缩不能解释上皮细胞的折叠。上皮细胞内的有丝分裂压力也不能解释折叠现象，因为在椭圆形期和三角形期，每个横切面上的上皮细胞数量没有差异，并且上皮管没有受到扩张限制。由微丝束介导的上皮细胞群的主动收缩被认为是导致折叠的原因。在所研究的所有阶段，微丝束都位于所有上皮细胞的顶端区域，并且位于那些占据正在形成的嵴顶部的细胞的基部区域。细胞松弛素B处理可阻止嵴的形成并破坏微丝束。
