GAMMA-TUBULIN IS REQUIRED FOR THE STRUCTURE AND FUNCTION OF THE MICROTUBULE-ORGANIZING CENTER IN DROSOPHILA NEUROBLASTS

We report that in Drosophila, gamma-tubulin is required for the struct ure as well as the function of microtubule organizing centres (MTOCs). This conclusion is based on the identification and phenotypic charact erization of a mutant allele of the gamma-tubulin gene located at regi on 23C of the polytene chromosome map. This mutation, which we have ca lled gamma-tub23C(PI), is caused by the insertion of a P-element withi n the 5' untranslated leader of the gamma-tubulin transcript. Northern and Western analyses show that gamma-tub23C(PI) is either a null or a very severe hypomorph as no gamma-tubulin mRNA or protein can be dete cted in mutant individuals. Visualization of DNA, MTOCs and microtubul es by confocal laser scanning microscopy of cells from individuals hom ozygous for gamma-tub23C(PI) reveals a series of phenotypic abnormalit ies. Some of these are similar to those observed after disruption of g amma-tubulin function in other organisms, including mitotic arrest and a dramatic decrease in the number of microtubules, but, in addition, we have observed that mutation in this gene also results in highly abn ormal MTOCs which show a variety of shapes and sizes which we never ob served in wild type cells. These results show that gamma-tubulin is re quired for both structural and functional roles in the MTOCs.