Environmental regulation of type X collagen production by cultures of limb mesenchyme, mesectoderm, and sternal chondrocytes.

We have examined whether the production of hypertrophic cartilage matrix reflecting a late stage in the development of chondrocytes which participate in endochondral bone formation, is the result of cell lineage, environmental influence, or both. We have compared the ability of cultured limb mesenchyme and mesectoderm to synthesize type X collagen, a marker highly selective for hypertrophic cartilage. High density cultures of limb mesenchyme from stage 23 and 24 chick embryos contain many cells that react positively for type II collagen by immunohistochemistry, but only a few of these initiate type X collagen synthesis. When limb mesenchyme cells are cultured in or on hydrated collagen gels or in agarose (conditions previously shown to promote chondrogenesis in low density cultures), almost all initiate synthesis of both collagen types. Similarly, collagen gel cultures of limb mesenchyme from stage 17 embryos synthesize type II collagen and with some additional delay type X collagen. However, cytochalasin D treatment of subconfluent cultures on plastic substrates, another treatment known to promote chondrogenesis, induces the production of type II collagen, but not type X collagen. These results demonstrate that the appearance of type X collagen in limb cartilage is environmentally regulated. Mesectodermal cells from the maxillary process of stages 24 and 28 chick embryos were cultured in or on hydrated collagen gels. Such cells initiate synthesis of type II collagen, and eventually type X collagen. Some cells contain only type II collagen and some contain both types II and X collagen. On the other hand, cultures of mandibular processes from stage 29 embryos contain chondrocytes with both collagen types and a larger overall number of chondrogenic foci than the maxillary process cultures. Since the maxillary process does not produce cartilage in situ and the mandibular process forms Meckel's cartilage which does not hypertrophy in situ, environmental influences, probably inhibitory in nature, must regulate chondrogenesis in mesectodermal derivatives. (ABSTRACT TRUNCATED AT 250 WORDS)