COMPARATIVE-ANALYSIS OF ENGRAILED-1 AND WNT-1 EXPRESSION IN THE DEVELOPING CENTRAL-NERVOUS-SYSTEM OF XENOPUS-LAEVIS

Expression of the Engrailed-1 (XEn-1) gene was studied in Xenopus embr yogenesis by Northern blot analysis and whole-mount in situ hybridizat ion. One transcript of 2.2 kb was detected from stage 17 (midneurula) onwards, until stage 47 (swimming tadpole). The expression pattern of the XEn-1 gene as revealed by in situ hybridization can be divided in three regions. The first domain of transient expression appears at the midneurula stage (st. 17) in the anterior part of the neural fold, fo rming a complete ring of positive cells at the mid/hindbrain border af ter neural tube closure. A second region of transient expression is de tected as groups of ventro-lateral cells in the spinal cord and the hi ndbrain from late-neurula till tadpole stages. A third area of transie nt expression of XEn-1 is formed by the anterior part of the developin g pronephros. Comparison of XEn-1 expression at the mid/hindbrain bord er with that of the Xenopus wnt-1 and engrailed-2 genes reveals that X En-1 and Xwnt-1, in contrast to XEn-2, are both detected in a narrow s tripe of positive cells in this region. Analysis in exogastrulated emb ryos reveals that expression of XEn-1 and Xwnt-1, but not XEn-2, is in duced by planar signaling in the presumptive midbrain, Of the three ge nes only XEn-1 is expressed in the floorplate at the mid/hindbrain bor der, while Xwnf-1 is expressed in adjacent cells in the neural ectoder m, The results suggest that in vertebrates at the interface between ce lls in the floorplate and in the paraxial neuroectoderm, at the limite d region of the mid/hindbrain border, En-1 interacts with wnf-1 in a s ignaling pathway analogous to the engrailed/wingless signaling in the parasegments of the Drosophila embryo.