[Cell-to-cell recognition in limb pattern formation].
Vertebrate limb is used as a model system to understand the mechanism of pattern formation in development. Mesenchymal cells of the limb bud are differentiated into chondrogenic cells or fibroblastic cells. The chondrogenic cells form bifurcated and segmented cartilage structure. This cartilage pattern is regulated by many signaling molecules and transcriptional factors. In the early stage of cartilage differentiation, mesenchymal cells aggregate into suitable region in the limb bud, and the aggregates form prepattern of skeletal elements. Cell adhesion molecules have been shown of their involvement in this cell aggregate formation and the cartilage differentiation process. Expression of these cell adhesion molecules and other cell surface molecules may be regulated by signaling molecules or transcriptional factors, although no regional specificities of these molecules have been reported. In this review, we describe about regional differences of cell affinity of limb bud mesenchyme. We show the differential cell affinity represents the positional identity of the mesenchyme in limb bud, and glycosylphosphatidylinositol (GPI) anchored cell surface proteins are involved in this different cell affinity. From these results, we discuss the importance of the cell affinity in pattern formation of limb bud.