THE EXPRESSION OF XIF3 IN UNDIFFERENTIATED ANTERIOR NEUROECTODERM, BUT NOT IN PRIMARY NEURONS, IS INDUCED BY THE NEURALIZING AGENT NOGGIN

The gene XIF3 encodes a neural-specific type-ill intermediate filament protein whose expression in the embryo precedes that of the neurofila ments by several hours. We now show, by in situ hybridization, that it is expressed at the neurula stage in primary neurons and, to a lesser extent, in undifferentiated anterior neuroectoderm. At the swimming t adpole stage, strong expression is restricted to the midbrain-hindbrai n boundary, even-numbered rhombomeres of the hindbrain and the Vth and VIIth cranial ganglia. XIF3 gene expression can be induced in ectoder mal cells (animal caps) derived from blastula when grown to the neurul a stage in the presence of the neuralizing agent noggin. In agreement with the proposed ability of noggin to neuralize, but not to promote n euronal differentiation, we find that the pattern of noggin-inducible XIF3 expression in animal caps is consistent with expression in undiff erentiated anterior neuroectoderm but not in primary neurons.