Environmental enhancement of in vitro chondrogenesis

In most in vitro tissue interaction studies, it is assumed that the negative control of the culture system (i.e., the tissue which does not differentiate when isolated) is representative of an in vivo situation, and that the isolated tissue is quite unable to differentiate without the interacting tissue. It is becoming increasingly obvious that the failure of isolated tissues to differentiate in vitro may be due to the techniques of the experimenter, not necessarily to metabolic deficiencies of the tissue. The results reported here show that while it is possible to demonstrate an effective interaction in which notochord promotes the differentiation of cartilage from somitic tissue, the negative result (somites alone failing to undergo chondrogenesis) applies only to a prescribed set of culture conditions. By substituting fetal calf serum and other nutrient supplements for horse serum, which was previously used in the nutrient medium, the incidence of in vitro chondrogenesis is markedly enhanced in somites cultured in the absence of notochord. The notochord therefore does not impose chondrogenic information upon the somites, it only permits or enhances a preexisting chondrogenic bias of the somites. In addition, DNA synthesis and proliferation were found to have only a desultory relation to chondrogenesis. The primary role of proliferation is to provide new cells for a continuing process of chondrogenic differentiation.