Smooth, a hnRNP encoding gene, controls axonal navigation in Drosophila.

We identified the gene smooth (sm) in a screen for genes that are specifically expressed within the lineage that forms the adult chemosensory bristles. sm is expressed in most or all differentiating neurones during embryogenesis, but is specifically expressed in the neurones of the adult chemosensory organs on the wings and legs during metamorphosis. The inactivation of sm results in axonal defects in the chemosensory neurones, in the inability of mutant flies to feed and in their precocious death. As sm belongs to a family of heterogeneous nuclear ribonucleoprotein (hnRNP), we propose that the control of axonal navigation and connectivity is partly achieved at the level of mRNA splicing or exporting.