Observations of Dependent Histogenesis in Salamander Limb Development

Abstract

ABSTRACT The prospective limb portion of the limb disc of Ambystoma punctatum and Taricha torosa tail-bud stages was transplanted homoplastically and heteroplastically to the ventral hypomere region of similar-aged host animals. The transplants were observed for growth (elongation) and for histogenesis of limb elements and in all cases less limb development was seen, both macroscopically and histologically, than was to be expected from the developmental age of the donors. In a parallel series of experiments a small amount of epibrachial somite tissue was transplanted with the limb cell mass to the ventral hypomere region. The limb histogenesis and growth were enhanced to a considerable degree. It was seen that chondrogenesis (of a girdle) occurred in the somite tissue and the limb cell mass seemed to demonstrate histogenesis (proximally) and elongation (distally) in relation to that development. The limb cell mass was transplanted to various superficial sites on the nonlimb trunk somites and it was observed that more advanced growth and histogenesis were obtained when the transplant was associated with the ventral somite region. Pronephric tissue was developed in all cases where limb cell mass was transplanted to the ventral hypomere region of Taricha torosa hosts. When the amount of dorsal tissue was increased, by adding dorsal ectoderm and/or epibrachial somite to the limb cell mass, no pronephric tissue developed in the graft area. No nephric differentiation was seen with similar transplants to Ambystoma punctatum hosts. The results are considered as indicative of a somite-dependent histogenesis in the development of the proximal portion of the transplanted limb.