Fig. 1. Progressive eye differentiation. A wild-type eye imaginal disc labeled for gene products that reveal pattern and differentiation is shown with anterior to the left. Arrowhead indicates the center of the morphogenetic furrow that separates anterior undifferentiated and posterior differentiating portions of the eye disc. Ahead of the morphogenetic furrow the Hairy protein accumulates in a rising gradient (blue). Hairy is downregulated just anterior to the morphogenetic furrow, just as levels of Ci155 peak (red). Ci155 protein is stabilized in response to Hh signaling. As R8 specification occurs within the morphogenetic furrow, Atonal activity is reported by expression of the target gene senseless (green). Sens expression is also maintained in the differentiating R8 cells posterior to the furrow.