Nika Yamazaki (from Tokyo Institute of Technology)
Our research interest is focused on the regulatory mechanisms of multigene families both in the immune and in the central nervous systems. In the immune system, somatic DNA recombination and gene conversion play important roles in the expression of antigen receptor genes. Gene rearrangement, known as V-(D)-J joining, not only generates a vast diversity in the receptor genes, but also activates a particular member of the gene family by bringing an enhancer element and promoter element into close proximity.
For the olfactory system, hundreds of odorant receptor genes have been reported, although it is yet to be studied how this multigene family is regulated for expression. It is known that each member of the gene family is expressed in one of the four topographically distinct zones, where olfactory neurons expressing one particular kind of receptor are randomly distributed Furthermore, it is assumed that a limited number of the receptor genes (possibly one) are activated in each olfactory neuron.
We have been studying how each neuron activates a limited number of the receptor genes keeping the rest of the genes silent. One obvious regulatory mechanism is at the level of transcription. In the mammalian immune system, DNA rearrangement is also utilized to activate one particular member of the receptor genes, and to exclude one of the two alleles (allelic exclusion). It is of interest to study whether such a mechanism is involved in the regulation of the olfactory system.
In order to study selective expression of the odorant receptor genes, we have been characterizing the genomic structure of the murine odorant receptor genes using genomic clones from the P1 phage library. Many P1 clones were found to contain multiple receptor genes, indicating that these genes are linked in tandem on the chromosome. We have extensively analyzed a P1 clone that contains two highly related (92% homologous) receptor genes, MOR28 and MOR10. It was found that these genes were expressed in the same zone in the olfactory epithelium, yet each gene was expressed in a different olfactory neuron. We are trying to understand the molecular mechanisms for the differential expression of the two highly related receptor genes.
Some odorant receptor genes are known to be expressed also in the testis, suggesting that they may be involved in maturation and/or chemotaxis of sperm cells. In order to elucidate the expression of the odorant receptor genes in the testis, we are currently characterizing a murine olfactory receptor gene which shares a significant homology with the HGMP07J gene isolated from a human testicular cDNA library.
For the study of mutually exclusive expression of the odorant receptor genes, we have generated transgenic mice which are forced to express one particular member of the receptors in every single olfactory neuron. The transgene contains the mouse receptor MOR28 gene under the control of OMP promoter. Since the OMP gene is expressed specifically in the olfactory epithelium, the transgenic receptor gene is expected to be activated in all mature neurons in the transgenic mouse. These studies will give us a new insight into the molecular mechanisms not only of the receptor gene expression, but also of neuronal projection in the olfactory bulb. When the olfactory neurons are regenerated, they send axons to the specific region called glomeruli in the olfactory bulb. It is amazing that axons are able to find a right target glomerulus out of two thousand similar structures. We are hoping that our transgenic approach will become a useful clue to study the target specificity and selectivity in the synapse formation.
Publication List:
Akamatsu, Y., Tsurushita, N., Nagawa, F., Matsuoka, M., Okazaki, K., Imai, M. and Sakano, H. (1994) Essential residues in V(D)J recombination signals. J. Immunol.153, 4520-4529.
Heike, T., Nishikomori, R., Kawai, M., Tsuboi, A., Arai, N. and Mikawa, H.(1994) Molecular basis for developmental changes of GM-CSF gene inducibility in embryonal carcinoma cells. Bioche. Biophys. Res. Comm.198, 473-479.
Heike, T., Nishikomori, R., Kawai, M., Tsuboi, A., Arai, N. and Mikawa, H.(1994) Developmental changes of GM-CSF gene inducibility in embryonal carcinoma cells. Mol. Immun.31, 1269-1275.
Kondo, T. and Ishiura, M. (1994) Circadian Rhythms of Cyanobacteria: Monitoring the Biological Clocks of Individual Colonies by Bioluminescence. J. Bacteriol.176, 1881-1885.
Kondo, T., Tsinoremas, N.F., Golden, S.S., Johnson, C.H., Kutsuna, S. and Ishiura M. (1994) Circadian Clock Mutants of Cyanobacteria. Science266, 1233-1236.
Matsuda, I., Masuda, E.M., Tsuboi, A., Behnam, S., Arai, N. and Arai, K. (1994) Characterization of NF(P), the nuclear factor that interacts with the regulatory P sequence (5'-CGAAAATTTCC-3') of the human interleukin-4 gene: relationship to NF-KB and NF-AT. Bioche. Biophys. Res. Comm.199, 439-446.
Tsuboi, A., Matsuda, E.S., Naito, Y., Tokumitsu, H., Arai, K. and Arai, N. (1994) Calcineurin potentiates activation of the granulocyte-macrophage colony-stimulating factor gene in T cells: involvement of the conserved lymphokine element 0. Mol. Biol. Cell5, 119-128.
Tsuboi, A., Muramatsu, M., Tsutsumi, A., Arai, K. and Arai, N. (1994) Calcineurin activates transcription from the GM-CSF promoter in synergy with either protein kinase C or NF-KB/AP-1 in T cells. Bioche. Biophys. Res. Comm.199, 1064-1072.
Watanabe, M., Muramatsu, M., Tsuboi, A. and Arai, K. (1994) Differential response of NF-KB1 pl05 and NF-KB2 p100 to HTLV-I encoded Tax. FEBS Letters342, 115-118.
Yoshimatsu, T. and Nagawa, F. (1994) Effect of artificially inserted introns on gene expression in Sacchromyces cerevisiae. DNA Cell Biol.13, 51-58.
National Insitute for Basic Biology
