DYNAMIC DEVELOPMENTAL EXPRESSION OF SMALLMINDED, A DROSOPHILA GENE REQUIRED FOR CELL-DIVISION

Here we describe the expression pattern of the smallminded (smid) gene during Drosophila development and investigate the phenotype of a null mutant. In situ hybridisation reveals the ubiquitous expression of sm id transcript throughout early embryonic stages until the extended ger m band stage, after which expression becomes localised to the neurogen ic ectoderm and gonad. Post-embryonic expression is restricted to tiss ues engaged in the developmental programme of the adult fly: the re-en larged neuroblasts; imaginal discs; histoblast nests; and precursors o f adult muscles. The correlation of smid expression with mitotic activ ity suggests a cell cycle function which is confirmed by the observed phenotype of a smid null mutant characterised by an abnormally small C NS, due to defective mitosis of post-embryonic neuroblasts and their s ubsequent death by apoptosis. (C) 1998 Elsevier Science Ireland Ltd. A ll rights reserved.