Meeting Abstract

13.2  Wednesday, Jan. 4  Developmental evidence that the metatarsals and phalanges are distinct modules WINSLOW, B. B.*; LEARY, B.; KAVANAGH, K.; University of Massachusetts Dartmouth

Historically metatarsals and phalanges have been considered as evolutionarily independent skeletal units in the autopod because of their functional and variational differences. However, during ontogeny these bones appear to develop from identical morphogenetic processes, using the same gene networks. This project aims to test the hypothesis that the metatarsals exist as a different developmental module than the phalanges. Specifically, each region should respond independently to experimental perturbations. Our data show that manipulations performed on the developing phalanges, such as the implantation of a foil barrier, can alter phalangeal patterns, indicating the presence of a proximal patterning signal. However, when the identical manipulations are applied to the metatarsal the phalanges develop normally, despite morphological changes to the metatarsal, suggesting the metatarsal-phalangeal joint separates two modules in the developing digit. To test the hypothesis that the metatarsal-phalangeal joint initiates the phalanges module, we experimentally manipulated the identity of the metatarsal-phalangeal joint via transplantation, manipulated proximal or distal signaling centers chemically, and assayed for patterning shifts in the phalanges. Phalangeal pattern is only altered by manipulations performed distal to the metatarsal-phalangeal joint, and not by manipulations proximal to the joint or to the identity of the joint itself. These data suggest that the metatarsal-phalangeal joint interzone itself does not provide signals specifying the sequential patterning of the digit (the “identity”), while metatarsal-phalangeal joint formation is clearly a critical stage creating a boundary in separating the metatarsal and phalanges modules.