DIFFERENTIAL LOCALIZATION OF MOX-1 AND MOX-2 PROTEINS INDICATES DISTINCT ROLES DURING DEVELOPMENT

Transcript localizations for Mox genes have implicated this homeobox g ene subfamily in the early steps of mesoderm formation. We have extend ed these studies by determining the protein expression profile of Mox- 1 and Mox-2 during mouse development. The time of onset of Mox protein expression has been accurately obtained to provide clues as to their roles during gastrulation. Expression of Mox-1 protein is first detect ed in the newly formed mesoderm of primitive streak stage mouse embryo s (7.5 days post-coitum, d.p.c.). In contrast, Mox-2 protein is first detected at 9.0 d.p.c. in the already formed somites. Additionally, im munostaining reveals new and distinct areas of Mox expression in the b ranchial arches and limbs that were not reported in our previous mRNA localization analysis. Mouse Mox-2 antibodies cross-react specifically in similar embryonic tissues in chick indicating the conservation of function of Mox genes in vertebrates. These expression data suggest th at the Mox genes function transiently in the formation of mesodermal a nd mesenchymal derivatives, after their initial specification, but bef ore their overt differentiation. Furthermore, while there appears to b e some overlap in protein expression between Mox-1 and Mox-2 during so mitogenesis, unique areas of expression indicate several distinct role s for the Mox genes during development.