Role of IroC in the fly olfactory system

Abstract

Sensory neurons, such as the visual and olfactory neurons, tend to express only one sensory receptor per neuron in order to prevent sensory overlap and then send their axons to particular target regions in the brain to form specific connections. The molecular mechanisms underlying either of these processes are largely unknown. The olfactory system represents an extreme example as only one receptor from a very large repertoire of receptor genes (up to 1200 in mouse) is selected for expression. The olfactory system of Drosophila represents an ideal system to study these mechanisms as it is quantitatively reduced and very well described. We have observed expression of a transcription factor family, IroC, in the maxillary palps, one of the two olfactory organs in the fly, and especially in the subset of olfactory receptor neurons, which coexpresses two olfactory receptor genes, OR33c and OR85e. IroC has previously been shown to regulate the coexpression of two rhodopsin genes in the fly retina and to contribute to retinal axon guidance. We thus aimed to identify the putative role of this family of transcription factors in the fly olfactory system by performing classical loss-of-function and gain-of-function experiments. Our results attribute three functions to IroC in the fly olfactory system. (i) Iro proteins repress the expression of OR33c and OR85e genes. (ii) Iro proteins may have a role in the specification of pb2B neurons from progenitor cells. (iii) Iro proteins contribute to the proper targeting of olfactory receptor neurons.