Department of Bioengineering
Associate Prof. ： Junji HIROTA
The sense of smell is intimately connected with the activities an animal undertakes in order to live and it has been preserved in a wide range of animal species from primitive times through to the present day. The olfactory system of mammals is capable of detecting millions of different types of chemicals in the environment. Olfactory sensory neurons (OSNs), the primary sensory neurons in the olfactory system, initiate the sense of smell by detecting odorants through odorant receptors (OR). These ORs G-protein coupled receptors with a putative seven-transmembrane domain structure. OR genes form the largest gene superfamily present in any genome analyzed so far . In mouse, approximately 1400 OR genes, 5% of its total gene count, have bee identified from the genomic sequence. The magnitude of this figure in itself indicates how important the sense of smell is to animals. OR genes also constitute the largest gene family in humans. The ‘efficacy of scent’ as represented by aromatherapy in recent years has led to a growing interest in how odorant molecules affects our bodies and emotions through the sense of smell.
At Hirota Laboratory, we are using molecular biology, mouse genetics and bio-imaging technology to study the olfactory system in mice. Our research programs are discussed below.
- Molecular mechanisms underlying expression of olfactory receptor genes
It is believed that an individual OSN expresses a single functional allele of a single OR genes, while all other OR genes remain silent. The mechanisms underlying this feature of ‘singular’ OR gene expression are not understood, but irreversible DNA rearrangements have been excluded by nuclear transfer experiments. We are studying the molecular mechanisms of OR gene regulation in order to understand how individual OSNs control the expression of such a large gene family.
Figure 1: analysis of olfactory receptor gene expression
- Molecular mechanisms for neuronal differentiation of olfactory sensory neurons
Olfactory nerve cells are unique among nerve cells in that they continually differentiate and regenerate themselves during the life of an organism. We are studying development and differentiation of OSNS from the stem cells to the mature OSNs.
Figure 2: Axon visualisation using a knock-in mouse