Global shape of Toll activation is determined by <i>wntD</i> enhancer properties.

Abstract

Buffering variability in morphogen distribution is essential for reproducible patterning. A theoretically proposed class of mechanisms, termed "distal pinning," achieves robustness by combining local sensing of morphogen levels with global modulation of gradient spread. Here, we demonstrate a critical role for morphogen sensing by a gene enhancer, which ultimately determines the final global distribution of the morphogen and enables reproducible patterning. Specifically, we show that, while the pattern of Toll activation in the early <i>Drosophila</i> embryo is robust to gene dosage of its locally produced regulator, WntD, it is sensitive to a single-nucleotide change in the <i>wntD</i> enhancer. Thus, enhancer properties of locally produced WntD directly impinge on the global morphogen profile.