Laboratories

Molecular and Cell Genetics

Prof. Kohno Assoc. Prof. Kimata
Professor
Kenji KOHNO
Associate Professor
Yukio KIMATA
Assistant Professor
Akio TSURU, Masaaki KOIKE
Labs HP
http://bsw3.naist.jp/kouno/

Outline of Research and Education

The endoplasmic reticulum (ER) is an important organelle in which newly synthesized secretory and membrane proteins are correctly folded and assembled. Numerous ER-resident molecular chaperones and catalysts are known to assist in this process. When cells are exposed to ER stress such as glucose starvation, disturbance of Ca2+ ion stores, and genetic mutations, unfolded and misfolded proteins accumulate in the ER. Accumulation of unfolded proteins in the ER is highly detrimental to the cell and the organism. To maintain ER homeostasis, cells induce at least three responses to overcome this deleterious condition (termed as UPR: unfolded protein response (Fig. 1), all of which increase the capacity of protein folding in the ER: (1) transcriptional upregulation of UPR target genes, (2) translational attenuation of protein synthesis, and (3) ER associated protein degradation (ERAD) . If this damage cannot be overcome, cells undergo apoptosis. Recent studies suggest that ER stress is a factor responsible for neurodegenerative disease, and that the regulation of this response plays an important role also in the development and differentiation of animals. We are conducting studies, with a goal of clarifying the quality control of protein folding in the ER and the physiological roles of UPR at each of the molecular, the cellular and the individual animal level. In other work in our lab, we have developed a simple and highly sensitive method for conditional cell ablation in transgenic mice, called "toxin receptor-mediated cell knockout (TRECK)". We have created mouse models of hepatitis and diabetes mellitus and are conducting studies on regenerative medicine, making use of these TRECK-Tg mice.

Major Research Topics

ER quality control and Unfolded Protein Response (UPR)

  • ER stress-sensing mechanism by IRE1.(Fig.2)
  • Molecular analysis of unconventional splicing in mammals.(Fig.3)
  • Physiological functions of IRE1α and IRE1β using KO mice.(Fig.4)
  • Analysis of a novel ER chaperone molecule DNAJB12.

We are focusing on the following projects: i) how IRE1 senses the accumulation of unfolded proteins in the ER, ii) how IRE1 recognizes and cleaves the target RNA on ER membrane , iii) the analysis of the downstream of UPR in yeast and mammalian cultured cells , iv) the physiological role of UPR activation in animals using ERAI mice and IRE1 knockout mice. Furthermore, active research is now under way concerning the molecular chaperones involved in protein folding in the ER.

Regenerative medicine, using TRECK-Tg mice

Using our unique TRECK method, we have created mouse models of hepatitis and diabetes mellitus. These TRECK-Tg mice are expected to be useful not only in developing new therapies but also in exploring tissue-stem cells of adult mice. We are attempting to apply these mouse models to regenerative medicine (isolation and identification of hepatic stem cells and pancreatic beta-stem cells) (Fig. 5).

References

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Fig.1 Unfolded Protein Response in yeast and mammals.
Fig.1 Unfolded Protein Response in yeast and mammals
Fig.2 Cluster formation (right) of yeast Ire1 under ER stress.
Fig.2 Cluster formation (right) of yeast Ire1 under ER stress
Fig.3 Unconventional splicing of XBP1 mRNA in mammalian IRE1α-XBP1 pathway.
Fig.3 Unconventional splicing of XBP1 mRNA in mammalian IRE1α-XBP1 pathway.
Fig.4 Distended ER morphology (right) in goblet cells from IRE1β KO mouse
Fig.4 The ER in IRE1β KO goblet cells is distended with misfolded mucin accumulation
Fig.5  Liver cell transplantation and regeneration in a mouse model of hepatitis.The donated liver cells (green) undergo regeneration throughout the recipient's liver (a mouse model of hepatitis). Left, a light image; right, a fluorescent image.
Fig.5  Liver cell transplantation and regeneration in a mouse model of hepatitis.The donated liver cells (green) undergo regeneration throughout the recipient's liver (a mouse model of hepatitis). Left, a light image; right, a fluorescent image.
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