As in lateral inhibition, the metalloprotease Kuzbanian, the EGF repeat 12 region of the Notch extracellular domain, Presenilin, and the Notch intracellular domain are required. Ectopic Notch signaling by Delta expression ahead of the morphogenetic furrow also causes premature differentiation. During proneural enhancement, the Notch intracellular domain overcomes the repression of neural differentiation. Delta47 clones than in neighboring tissue, and it soon reaches high levels. The senseless gene is expressed in response to ato activity.
Daughterless protein is ubiquitous but upregulated in ato -expressing cells of the furrow.
These findings suggest a model for proneural enhancement. The mechanism contrasts with lateral inhibition. The ato gene could be a direct target of proneural enhancement. Another candidate is daughterless , which encodes a bHLH heterodimer partner of Ato that is required for Ato function in eye development. A third candidate is senseless , a zinc finger protein that enhances and maintains proneural gene expression.