The role of somites in the growth and early development of mouse limb buds

Abstract

Organ culture techniques were employed to study the developmental potential of embryonic mouse limbs. Isolated limb buds from 12- and 13-day embryos grew well and, after 6 days in culture, well-defined scapula, humerus, radio-ulna, and digits were evident. In contrast, the growth of forelimbs from 11th day embryos was poor even when cultured for 9 days and, in most cases, different cartilaginous segments were not recognizable. Inclusion in the forelimb explant of the adjacent somitic region markedly improved the chondrification in these limbs so that the extent and pattern of cartilage development was now essentially similar to that observed in the older limbs. To investigate the nature of the role of somitic tissue during early limb development, “mixed explants” consisting of [ 3H]thymidine-labeled somitic tissue and unlabeled limb buds were grown in vitro for 9 days and the cultures were processed for autoradiography. Examination of the autoradiograms revealed the presence of a large number of labeled cells in the humeral cartilage. The conclusion is drawn that while the older limbs (from 12- and 13-day mouse embryos) are self-differentiating, the same is not true of the limbs that are in an earlier stage of development (from 11-day embryos). In the latter case, cellular contribution from the adjacent somitic region is necessary and critical for the optimum growth and differentiation of these limbs. Whether this property is specific and exclusive to somitic tissue or any other tissue mass is equally capable of this role remains unresolved.