Tissue patterning mechanisms of facial prominences in chicken embryo

局部模式事件发生在额鼻肿块内，这是胚胎口腔周围的面部隆起之一。在鸡胚中，上喙主要由前鼻肿块形成，即位于鼻缝之间的突出部分。在本研究中，我们从额鼻肿块的外侧和中央三分之一分离间充质，并比较形成单个软骨棒的能力。我们发现中央三分之一的细胞颗粒与面部上皮结合有形成直软骨棒的趋势，而来自外侧三分之一的细胞产生更多的分枝状生长。在外侧细胞和中心细胞混合的重组细胞球中，中心细胞聚集在软骨凝聚体中，而外侧细胞分布在整个移植物中。中央细胞球比外侧细胞球含有更多的潜在软骨细胞。为了观察细胞颗粒中-外侧模式是否重新建立，我们使用Msx-2作为第24期外侧间质的标记物。中心细胞颗粒重组不表达基因或开启双侧表达。移植的侧侧细胞在移植后48小时维持并上调Msx-2的表达，但不能建立双侧对称性。由中央和外侧第三间质混合而成的细胞微球通常表达3块Msx-2转录本。因此，额鼻肿块的中心区域可能在24期含有大部分软骨前细胞，这些细胞有从周围非软骨间质分离的倾向。Msx-2可能有助于在细胞分化之前建立中央和外侧间质之间的差异。

Local patterning events occur within the frontonasal mass, one of the facial prominences that surrounds the embryonic oral cavity. In the chicken embryo, the upper beak is primarily formed by the frontonasal mass, the prominence that lies between the nasal slits. In the present study we dissociate mesenchyme from the lateral and central thirds of the frontonasal mass and compare the ability to form a single cartilage rod. We find that central third cell pellets combined with facial epithelium have a tendency to form a straight cartilage rod whereas the cells from the lateral third produce more branched outgrowths. In the reconstituted cell pellets with lateral and central cells mixed together, the central cells aggregate in the cartilage condensations while lateral cells are distributed throughout the graft. The central cell pellets contain greater numbers of potential chondrogenic cells than lateral cell pellets.To see whether medio-lateral patterning is re-established in the cell pellets, we used Msx-2 as a marker for the lateral mesenchyme at stage 24. Central cell pellet recombinations do not express the gene or turn on bilateral expression. Grafts of lateral cells maintain and up-regulate Msx-2 expression 48 hours after grafting, but are not able to establish bilateral symmetry. The cell pellets that are mixtures of central and lateral third mesenchyme often express three patches of Msx-2 transcripts. Thus the central region of the frontonasal mass probably contains the majority of prechondrogenic cells at stage 24 and these cells have a tendency to segregate from the surrounding non-chondrogenic mesenchyme. Msx-2 may help to set up the differences between central and lateral mesenchyme prior to cell differentiation.