[Development of the nervous system in Drosophila]

The formation of sense organs in Drosophila involves a series of choices, each of which depends on the co-ordinated activity of a small battery of genes. Two essential steps of this process have been extensively studied over the past few years: the determination of neural precursor cells, and their diversification. In both cases, the choices are dichotomous, and each choice reflects the fact that a specific control gene is or is not expressed. This principle is illustrated in the case of the genes "cut" and "poxn", the expression of which controls the type of sense organ that a given precursor will form.