The circumblastoporal and notochordal expression of T, which are temporally contiguous in Xenopus, are separated in Gastrotheca, implying that distinct regulatory mechanisms may control the expression of T in its two domains. The separation of the T pattern also indicates that involution at the blastopore is separate from notochord formation. In addition, extension of the archenteron and notochord occurs after blastopore closure, suggesting that dorsal convergence and extension have been delayed until after blastopore closure. Therefore, dorsal convergence and extension need not be the cause of blastopore closure in Gastrotheca. The separation of gastrulation events in embryos that have not been experimentally manipulated, such as those of Gastrotheca, helps in understanding the distinct nature of gastrulation processes.
Limb buds appear early and develop continuously through embryonic life.
The capacity for autonomous development of E. coqui limb buds was tested by explanation and transplantation. When limb buds were explanted to in vitro culture, they progressed for a few stages and then arrested. Since limb buds transplanted to various sites on E. coqui embryos tended to develop completely, the limited development of the explants in vitro and the transplants to R. pipiens suggests the presence of a systemic factor in the embryo involved in the normal continuous growth of E. coqui legs. Attempts to demonstrate a role for thyroid hormone have thus far been unsuccessful. To investigate this phenomenon, we have examined the developmental expression of arginase in the direct developing frog Eleutherodactylus coqui.