A POLARITY FIELD IS ESTABLISHED EARLY IN THE DEVELOPMENT OF THE DROSOPHILA COMPOUND EYE

The photoreceptors within the ommatidia of the Drosophila compound eye form a trapezoid. This occurs in two chiral forms in the dorsal and v entral half of the eye. We have used two manipulations to induce ectop ic ommatidia, in combination with molecular markers for specific posit ions in the retinal field. We find that ectopic morphogenetic furrows induced on the eye field margin (or midline) and those induced in the body of the field have different consequences for the establishment of retinal polarity. Furthermore, the dorsal/ventral vector held is esta blished early in development, prior to and independent of the initiati on of the morphogenetic furrow. An 'early equator' model is presented to account for these and previously published data. (C) 1997 Elsevier Science Ireland Ltd.