Lack of association between avian cartilages of different embryological origins when maintained in vitro

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Abstract
The possibility that cartilages of differing embryological origins behave as separate types with respect to cell‐to‐cell associations was tested by placing the cut ends of transversely sectioned embryonic chick tibial cartilages (of mesodermal origin) in apposition to transversely sectioned Meckel's cartilages (a neural crest (ectodermal) cartilage) on the surface of a semi‐solid organ culture medium and maintaining the combinations in vitro for five to ten days. Tibia‐tibia and Meckel's cartilage‐Meckel's cartilage (homotypic) combinations, which served as controls, became united by a common extracellular matrix and by the proliferation of chondroblasts. Analysis of combinations where one partner had been prelabelled with 3H‐thymidine indicated that chondroblasts intermingled at the contact zone. In contrast, tibia‐Meckel's cartilage (heterotypic) combinations became separated by a layer of fibrous tissue. The chondroblasts at the contact zone failed to intermingle. We conclude that avian embryonic chondrocytes are not all equivalent and that part of their non‐equivalence could be related to their embryological origin either from the mesoderm or from the ectodermal neural crest.