Independence of the numbers of legs and leg ganglia in Drosophila bithorax mutants

Abstract

A prominent feature of most central nervous systems is the presence of highly organized association centres, often called ‘nuclei’ in vertebrate brains and ‘glomeruli’ or ‘neuromeres’ in invertebrate brains and ventral ganglia. As little is known of the processes leading to the formation of these centres, we have investigated this question in the case of the leg neuromeres of Drosophila. The thoracico-abdominal ganglion of wild-type flies contains six conspicuous neuromeres, each associated with a leg¹. In bithoraxoid (bxd) mutants, the first abdominal segment is transformed to thoracic, and one or two additional legs may develop². We show here that supernumerary neuromeres may also be observed in this mutant. However, in a given individual the number of neuromeres is independent of the number of legs. In Hyperabdominal (Hab) mutants, the metathoracic segment is transformed to abdominal, and the metathoracic legs may be missing³. The ganglia of four-legged mutants show a variable reduction of the metathoracic leg neuromeres. We conclude that the formation of a leg neuromere is genetically controlled and does not depend on the presence of a corresponding leg.