CONICET | Buscador de Institutos y Recursos Humanos

During Xenopus laevis gastrulation, the involuting mesoderm layer organizes in different regions: head mesoderm, chordamesoderm, paraxial mesoderm and lateral plate mesoderm. Head mesoderm gives rise to the cardiac and head muscles together with some of the skulls bones, while paraxial mesoderm gives rise to somites, which generate the muscles and bones of the trunk. Although both mesoderm regions deliver the same tissue types, they show distinct developmental programs. In order to elucidate the molecular profile of the head mesoderm and its relation to paraxial mesoderm we analyzed the expression pattern of different molecular markers in the context of the head-trunk patterning. We show that head mesoderm is molecularly different from paraxial mesoderm. Head mesoderm expresses Tbx1 and Pitx2; these markers show an anteroposteriorly and dorsoventrally regionalized and overlapping expression. The trunk molecular setup between stage 11 and 17 was analyzed by studying the expression pattern of pMesogenin1 and Tbx6. These markers are zygotically expressed and developmentally regulated in presumptive and paraxial mesoderm. These molecular differences are correlated with morphological differences. It is well established that Retinoic Acid (RA), through Hox genes is involved in the patterning of the somitic mesoderm giving trunk identity. In this context it is possible that head mesoderm is not under the influence of RA. To prove this hypothesis we also analysed the expression pattern of RALDH2 (RA synthesis enzyme) and Cyp26 (RA hydroxylase). Alterations in the head-trunk mesoderm patterning were caused by overexpression of Cyp26. These findings in amphibian mesoderm lead us to suggest that head and paraxial mesoderm molecular pattern is evolutionary conserved, since a similar molecular setup was observed in avian embryo