Molecular mechanisms of cell adhesion corresponding to positional values in limb bud

在脊椎动物肢体发育过程中，发育带的肢体间充质细胞根据位置的不同形成软骨形态。肢体芽细胞利用细胞表面分子来识别周围细胞的位置值。利用不同位置值的鸡肢间质进行细胞分选实验，发现了细胞表面分子的差异。在单层培养中，不同发育阶段或不同位置的间充质细胞混合时发生分选。分选过程独立于成软骨能力发生，每个分选区域的中心形成软骨结节。不同位置值的间充质细胞即使在不能附着形成聚集体的琼脂上也能进行分选，说明分选的发生不是取决于细胞基质的差异，而是取决于细胞-细胞亲和力的差异。为了鉴定控制位置值相关细胞粘附的细胞粘附分子，我们首先利用RT-PCR技术克隆了鸡肢芽中表达的cadherin超家族基因cDNA。原钙粘蛋白2是人原钙粘蛋白Pcdh2的同源物。原钙粘蛋白2的表达模式提示其与细胞分选密切相关。我们制备了鸡肢芽间质细胞表面分子单克隆抗体，抑制了不同发育阶段发育带细胞之间的分选。

In vertebrate limb development, limb mesenchyme cells in the progress zone form cartilage pattern depending on the positional values allotted to them. The limb bud cells are though to use cell surface molecules to recognize the positional values of their surrounding cells.We have found the difference in cell surface molecules from the cell sorting experiment using chick limb mesenchyme with different positional values. The sorting out in monolayr culture occurred when the mesenchymal cells at different developmental stages or from different positions were mixed. The sorting out occurred independently of chondrogenic potency and cartilage nodules were formed in the center of each sorted area. The mesenchymal cells with different positional values were sorted even on agar where cells could not attach and form aggregates, suggesting the sorting out occurs depending on the difference on not cell-substratum but cell-cell affinity.To identify cell adhesion molecules which control the positional value-related cell adhesion, we first cloned cDNA of cadherin superfamily genes expressing in chick limb bud with RT-PCR.Protocadherin 2, a homologue of human protocadherin Pcdh2, was identified. The expression pattern of protocadherin 2 suggests its close relationship to cell sorting.We have raisd a monoclonal antibody to the cell surface molecular of chick limb bud mesenchyme, which inhibited the sorting out between the progress zone cells at different developmental stages.