EPIDERMAL INDUCTION AND INHIBITION OF NEURAL FATE BY TRANSLATION INITIATION-FACTOR 4AIII

Bone Morphogenetic Protein-4 (BMP-4) is a potent epidermal inducer and inhibitor of neural fate, We have used differential screening to iden tify genes involved in epidermal induction downstream of BMP-4 and rep ort here evidence of a novel translational mechanism that regulates th e division of the vertebrate ectoderm into regions of neural and epide rmal fate, In dissociated Xenopus ectoderm, addition of ectopic BMP-4 leads to an increase in the expression of translation initiation facto r 4AIII (eIF-4AIII), a divergent member of the eIF-4A gene family unti l now characterized only in plants, In the gastrula embryo, Xenopus eI F-4AIII (XeIF-4AIII) expression is elevated in the ventral ectoderm, a site of active BMP signal transduction. Moreover, overexpression of X eIF-4AIII induces epidermis in dissociated cells that would otherwise adopt a neural fate, mimicking the effects of BMP-4. Epidermal inducti on by XeIF-4AIII requires both an active BMP signaling pathway and an extracellular intermediate. Our results suggest that XeIF-4AIII can re gulate changes in cell fate through selective mRNA translation, We pro pose that BMPs and XeIF-4AIII interact through a positive feedback loo p in the ventral ectoderm of the vertebrate gastrula.