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

在脊椎动物肢体发育中，进展区的肢体间充质细胞根据分配给它们的位置值形成软骨图案。肢芽细胞是通过细胞表面分子来识别周围细胞的位置值，我们通过对不同位置值的鸡肢间充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，当不同发育阶段或不同部位的间充质细胞混合在一起时，就会出现分选。分选与软骨形成能力无关，并在每个分选区域的中心形成软骨结节。不同位置的间充质细胞即使在细胞不能附着并形成聚集体的琼脂上也能被分选出来，这表明这种分选不是根据细胞底物的不同而是细胞与细胞之间的亲和力的不同而发生的。为了鉴定控制与位置值相关的细胞黏附的细胞黏附分子，我们首先用RT-PCR方法克隆了在鸡肢芽中表达的钙粘蛋白超家族基因的cDNA.Protocadherin-2的表达模式提示其与细胞分选密切相关。我们针对鸡肢芽间充质细胞表面分子，提出了一种抑制不同发育阶段进展区细胞分选的单抗。

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.