A comparative analysis of frog early development

The current understanding ofXenopus laevis development provides a comparative background for the analysis of frog developmental modes. Our analysis of development in various frogs reveals that the mode of gastrulation is associated with developmental rate and is unrelated to egg size. In the gastrula of the rapidly developing embryos of the foam-nesting frogsEngystomops coloradorum andEngystomops randi , archenteron and notochord elongation overlapped with involution at the blastopore lip, as inX. laevis embryos. In embryos of dendrobatid frogs and in the frog without tadpolesEleutherodactylus coqui , which develop somewhat more slowly thanX. laevis , involution and archenteron elongation concomitantly occurred during gastrulation; whereas elongation of the notochord and, therefore, dorsal convergence and extension, occurred in the postgastrula. In contrast, in the slow developing embryos of the marsupial frogGastrotheca riobambae , only involution occurred during gastrulation. The processes of archenteron and notochord elongation and convergence and extension were postgastrulation events. We produced an Ab against the homeodomain protein Lim1 fromX. laevis as a tool for the comparative analysis of development. By the expression of Lim1, we were able to identify the dorsal side of theG. riobambae early gastrula, which otherwise was difficult to detect. Moreover, the Lim1 expression in the dorsal lip of the blastopore and notochord differed among the studied frogs, indicating variation in the timing of developmental events. The variation encountered gives evidence of the modular character of frog gastrulation.