| The use of neural maps to encode information is a fundamental organizational principle of sensory nervous systems. In the olfactory system, olfactory receptor neurons that express the same odorant receptors are dispersed in the peripheral olfactory organs while their axons project to the same olfactory unit, the glomerulus, in the brain. The molecular and cellular mechanisms for the formation of this 'odortopic' map remain largely unknown.;The Drosophila antennal lobe, which is analogous to the olfactory bulb in vertebrates, has emerged as a powerful model system to study olfactory development, given its advantages in genetic tractability and cellular simplicity. Although much progress has been made in understanding of neuronal contributions to the formation of the antennal lobe, little is known about the roles of glia in olfactory development. In this study, a new population of glia, TIFR glia (transient-interhemispheric-fibrous-ring glia), was identified and shown to be necessary for the midline crossing of the olfactory axons and important for glomerular development in the antennal lobes. Neuroglian, a member of the L1 family of cell adhesion molecules, was found to be expressed in the glia as well as the olfactory neurons. Phenotypic and genetic analyses demonstrated that Neuroglian functions in the morphogenesis of the TIFR glia, which in turn regulates olfactory axon midline guidance.;In addition to the interaction between neurons and glia, cell-cell interactions were also observed between the olfactory neurons and their synaptic partners, the projection neurons. The presynaptic expression of a hyperactive version of the Limk gene, encoding a serine/threonine kinase and an important regulator of cytoskeletal dynamics, changed the dendritic projection of projection neurons and formed ectopic glomeruli at the midline. The finding supports a powerful role of olfactory neurons in the formation of the olfactory circuit.;The human orthologs of Neuroglian and Limk have been linked to human nervous system diseases, CRASH syndrome and Williams syndrome, respectively. The characterization of these two conserved genes in the Drosophila brain extends our knowledge of their cellular functions and helps to shed light on the pathology of human genetic diseases. |
