THE HOMEOTIC TARGET GENE CENTROSOMIN ENCODES AN ESSENTIAL CENTROSOMALCOMPONENT

The centrosomin (cnn) gene encodes a protein associated with mitotic c entrosomes in Drosophila melanogaster and is a target of homeotic gene regulation. Here we report that CNN is an essential component of the centrosome. Loss of zygotic cnn expression disrupts the development of the second midgut constriction, the gastric caeca, and the nervous sy stem. Embryos that lack maternal as well as zygotic cnn expression dis play defects in nuclear division, chromosome alignment, and microtubul e organization, while adult flies that are mosaic for cnn(-) cells exh ibit defects indicative of a block in cell proliferation. We propose t hat cnn provides an example of homeotic genes directly regulating the accumulation of essential cellular proteins to carry out segment-speci fic morphogenetic functions.