Genetics of epithelial polarity and pattern in the Drosophila retina

This review is focused on recent advances in our understanding of the devel opment of coordinated cell polarity, through experiments on the Drosophila compound eye, Each eye facet (or "ommatidium") contains a set of eight phot oreceptor cells, placed so that their rhabdomeres form an asymmetric trapez oid. The array of ommatidia is organized so that these trapezoids are align ed in two mirror-image fields, dorsal and ventral to the eye midline (or "e quator"). The development of this pattern depends on two systems of positio nal information that inform the cluster of cells that will form an ommatidi um of anterior/posterior (a/p) and dorsal/ventral (d/v) direction. The form er (a/p) is encoded by a progressive wave of development (the morphogenetic furrow). The tatter (d/v) involves molecules known to act in tissue polari ty in other organs and organisms. Our understanding of the function of thes e molecules rests not only on their mutant phenotypes, biochemistry, and ex pression patterns, but also on the spatial effects when mutant patches of c ells are made (genetic mosaics). BioEssays 21:275-285, 1999. (C) 1999 John Wiley & Sons, Inc.