Aspects of spinal cord induction of chondrogenesis in chick embryo somites

Abstract

ABSTRACT The specificity of the chondrogenic inductive activity of chick embryonic spinal cord has been examined in chorioallantoic culture. It has been found that the 2-day spinal cord is capable of inducing somites to chondrify even after lethal X-irradiation (5000 rads, i.e. 50 J/l kg); this dose of X-radiation resultingin the inhibition of mitosis in the spinal cord and its complete necrosis within 48 h of irradiation. The unirradiated spinal cord is capable of promoting the chondrogenesis of stage 9 –12 posterior lateral mesoderm, but to a lesser extent than when it is combined with stage 9 –12 posterior somite mesoderm. Irradiated spinal cord, however, possesses no chondrogenic activity with respect to lateral mesoderm. Thus it would appear that the 2-day spinal cord possesses a general cartilage-promoting activity dependent on its continued viability and proliferation, in addition to a somite-specific chondrogenic activity that survives a lethal dose of X-radiation. The inclusion of enzymes in the Millipore filter used as a graft vehicle has been used to demonstrate that collagenase and hyaluronidase when combined, but not individually, are capable of interfering in the induction of somite chondrogenesis by irradiated spinal cord. Grafts of somites with unirradiated spinal cord show that these enzymes do not directly reduce the chondrogenic potential of the somites or interfere in the subsequent deposition of cartilage matrix. The activity of the spinal cord in inducing somite chondrogenesis appears to be associated with the synthesis of basement membrane materials by either or both of the interacting tissues during the first 24 h of the interaction. No influence of the 2-day spinal cord on the morphogenesis of non-somitic cartilage could be detected.