Developmental pattern and molecular identification of globin chains in Xenopus laevis

High-resolution electrophoresis of larval and adult hemoglobins of Xenopus laevis reveals stage-specific differences in the number and mobility of the globin chains. To establish the relationship between the globin chains and the previously described globin genes, the corresponding mRNAs were hybrid-selected from total erythroblast RNA by representative cDNA clones, and translated in vitro. Electrophoretic separation of the translation products allowed identification of a major and a minor α-globin chain in the larval and adult stages. This also holds for the adult β-chains, however in the larval stage a difference in abundance is only detectable in the β-mRNAs, but not in the translation products, because they comigrate. The fact that major and minor globin chains can be assigned to genes, which are located in two clusters, suggests that the related genes are expressed coordinately, but at different levels. Analysis of the globin patterns during development reveals that transition from the larval to the adult globin chains coincides with metamorphosis. Moreover, there is evidence of two globin chains that are only expressed in early larval stages and hence might be related to additional larval β-globin genes of as yet unknown genomic location.