Wedden S E, Ralphs J R, Tickle C
Department of Anatomy, University College & Middlesex School of Medicine, London, UK.
Development. 1988;103 Suppl:31-40. doi: 10.1242/dev.103.Supplement.31.
Pattern formation is the developmental process that leads to the spatial ordering of cell differentiation. We have explored the problem of pattern formation in the development of the face of chick embryos. At early stages, the developing face consists of a series of small buds of tissue, the facial primordia that encircle the primitive mouth. The concepts of positional information provide a framework for considering how the patterns of differentiated cells are generated in the face. We suggest that the cranial neural crest cells must first be informed to which facial primordium they belong and then of their position within that primordium. The cells of the early primordia appear indistinguishable. However, when the mesenchyme cells are placed in high-density culture, cartilage differentiates. The extent and pattern of cartilage differentiation is characteristic for the cell population of each facial primordium. Myogenic cells also differentiate in the cultures, but the proportion of myogenic cells is independent of the extent of chondrogenesis. Within the facial primordia, a set of epithelial-mesenchymal interactions appears to be required for outgrowth and pattern formation along the proximodistal axis of the chick beaks. In culture, face epithelium locally inhibits cartilage differentiation and suggests that another set of epithelial-mesenchymal interactions may be involved in cell patterning. The mechanisms involved in specifying the mediolateral axis of the face, for example, the midpoint of the upper beak, are not known. Vitamin A derivatives, collectively known as retinoids, affect the development of the face of chick embryos and lead to a specific facial defect. Upper beak development is inhibited but the lower beak develops normally. The response to retinoids could be related to the specification of cells to belong to the facial primordium that will form the upper beak. Alternatively, retinoids may interfere with positional cues that operate to inform cells of their position within that primordium.
模式形成是导致细胞分化空间排序的发育过程。我们探讨了鸡胚面部发育过程中的模式形成问题。在早期阶段，发育中的面部由一系列小的组织芽组成，即围绕原始口的面部原基。位置信息的概念为思考面部如何产生分化细胞模式提供了一个框架。我们认为颅神经嵴细胞必须首先被告知它们属于哪个面部原基，然后是它们在该原基内的位置。早期原基的细胞看起来难以区分。然而，当间充质细胞置于高密度培养中时，软骨会分化。软骨分化的程度和模式是每个面部原基细胞群体的特征。成肌细胞在培养物中也会分化，但成肌细胞的比例与软骨形成的程度无关。在面部原基内，一组上皮 - 间充质相互作用似乎是鸡喙沿近远轴生长和模式形成所必需的。在培养中，面部上皮局部抑制软骨分化，这表明另一组上皮 - 间充质相互作用可能参与细胞模式形成。例如，确定面部内外侧轴（如上喙中点）的机制尚不清楚。维生素A衍生物，统称为类视黄醇，会影响鸡胚面部的发育并导致特定的面部缺陷。上喙发育受到抑制，但下喙正常发育。对类视黄醇的反应可能与细胞归属于将形成上喙的面部原基的指定有关。或者，类视黄醇可能会干扰用于告知细胞在该原基内位置的位置线索。
