Tickle C, Crawley A, Farrar J
Department of Anatomy and Developmental Biology, University College and Middlesex School of Medicine, London, UK.
Development. 1989 Aug;106(4):691-705. doi: 10.1242/dev.106.4.691.
Local application of retinoic acid to wing buds of chick embryos leads to dose- and position-dependent changes in the pattern of cellular differentiation. Early effects of retinoid treatment on the apical ectodermal ridge coordinate pattern changes and morphogenesis. The length of the apical ridge increases when additional digits will form but decreases when digits are lost. These changes in length can be understood in terms of a threshold response to the local retinoid concentration that results in either disappearance or maintenance of the ridge (Lee & Tickle, J. Embryol. exp. Morph. 90, 139-169 (1985)). Here, we have analysed the mechanisms involved in ridge disappearance by locally applying retinoic acid to the apex of stage 20 chick wing buds. With this treatment regime, low doses give duplicated digit patterns and higher doses truncations. The height of the apical ridge is progressively reduced with increasing doses of retinoid and the time course of ridge flattening indicates that the height of the ridge is correlated with bud outgrowth. With high doses of retinoic acid, the typical ridge, a pseudostratified epithelium in which the columnar cells are tightly packed, disappears and the epithelium at the tip of the bud consists of loosely packed cuboidal cells. Shortly after treatment, there is a decrease in the number of gap junctions between ridge cells. This early change in cell contacts suggests that gap junctions may be involved in maintaining epithelial morphology. When treated epithelium is recombined with untreated mesenchyme, an apical ridge is reestablished and distal structures can be generated. In contrast, when treated mesenchyme is recombined with the epithelium from normal buds, only proximal structures are formed. Therefore, retinoids can lead to a reorganization of the apical ectodermal ridge which is mediated and maintained by the mesenchyme.
将视黄酸局部应用于鸡胚的翅芽会导致细胞分化模式出现剂量和位置依赖性变化。类视黄醇处理对顶端外胚层嵴的早期影响协调了模式变化和形态发生。当额外的指将形成时，顶端嵴的长度增加，但当指缺失时，其长度减小。这些长度变化可以根据对局部类视黄醇浓度的阈值反应来理解，该反应导致嵴的消失或维持（Lee和Tickle，《胚胎学与实验形态学杂志》90，139 - 169（1985））。在这里，我们通过将视黄酸局部应用于第20阶段鸡胚翅芽的顶端，分析了嵴消失所涉及的机制。在这种处理方案下，低剂量会产生重复的指模式，高剂量会导致截断。随着类视黄醇剂量的增加，顶端嵴的高度逐渐降低，并且嵴变平的时间进程表明嵴的高度与芽的生长相关。使用高剂量视黄酸时，典型的嵴，即柱状细胞紧密排列的假复层上皮会消失，芽顶端的上皮由排列松散的立方体细胞组成。处理后不久，嵴细胞之间的间隙连接数量减少。这种细胞接触的早期变化表明间隙连接可能参与维持上皮形态。当处理过的上皮与未处理的间充质重组时，顶端嵴会重新建立，并且可以产生远端结构。相反，当处理过的间充质与正常芽的上皮重组时，仅形成近端结构。因此，类视黄醇可导致顶端外胚层嵴的重组，这由间充质介导并维持。
