Ectoderm-mesoderm interactions in relation to limb-bud chondrogenesis in the chick embryo: transfilter cultures and ultrastructural studies.

Limb ectoderm induces cartilage differentiation in mesoderm from chick embryo limb buds, Transfilter cultures have shown that this interactions requires 'contact' conditions and cannot take place at a distance. In vivo, a basement membrane is always present between ectoderm and mesoderm. The present paper demonstrates that the relationship between ectoderm and mesoderm is similar in vivo and in transfilter cultures. In culture conditions, the filter appears to be infiltrated by mesodermal cell outgrowths which form a continuous mesodermal cover on the filter. A basement membrane is always present between the mat of mesodermal cell processes and the ectoderm. Mesodermal cell processes are able to cross the Nuclepore filters (pore size 0.6-0.8 micrometer) within 15 min. After 2 h in culture, the surface of the filter opposite to the mesodermal explant is completely covered with mesodermal outgrowths. The extracellular material accumulating at the ectoderm-mesoderm interface appears to be mainly of mesodermal origin.