Neural development in the marsupial frog Gastrotheca riobambae

The expression pattern of the tyrosine kinase gene Pag in whole-mount preparations of Gastrotheca riobambae embryos and the immunostaining of embryos against the proteins vimentin, NCAM, Pax-2, Hoxd9, and antigen 2G9 allowed detection of migrating streams of cranial neural crest (NC) cells, the isthmus, the hindbrain boundaries, rhombomeres, cranial nerves, and the developing spinal cord. Expression patterns of these genes and the basic neural morphology of Gastrotheca have been conserved in comparison with other vertebrates. However, as in Xenopus, a prominent stream of migrating cranial NC cells from rhombomere 5 was found in Gastrotheca embryos. By contrast, in chick embryos, premigratory NC cells from rhombomeres 3 and 5 undergo extensive apoptosis, which suggests that in anurans, apoptosis of the cranial NC may deviate from the chick pattern. The branchial-anterior and branchial-posterior masses of cranial NC cells, that populate the gill arches, are very large in G. riobambae. We cannot distinguish whether this feature corresponds to an anuran trait related to development of the tadpole pharyngeal skeleton, or is related to development of the peculiar external bell gills of this frog. This work provides the descriptive groundwork for lineage studies of the NC in G. riobambae embryos. Gastrotheca embryos are large and flat, have prominent streams of cranial NC cells, and develop very large external bell gills. These unique characteristics may facilitate future comparative analysis of the role of apoptosis in patterning the amphibian NC cell streams, and the contribution of the NC to development of the gills.