| Co-Investigator(Kenkyū-buntansha) |
SEO Hisao Research Institute of Environmental Medicine, Nagoya Universaity, Professor, 環境医学研究所, 教授 (40135380)
MURATA Yoshihara Research Institute of Environmental Medicine, Nagoya Universaity, Professor, 環境医学研究所, 教授 (80174308)
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| Research Abstract |
We identified ZAKI-4 as a thyroid hormone responsive gene in cultured human skin fibroblasts. We examined the temporal and spatial expression patterns of ZAKI-4 messenger RNA (mRNA) in control and hypothyroid rat brains. Northern blot analysis revealed that ZAKI-4 mRNA was detected in both cerebral cortex and cerebellum as early as embryonic day (E) 1 8. In the cerebral cortex, the expression level gradually increased with age, reaching a plateau at postnatal day (P) 7 and remained constant thereafter until P30. A similar pattern of increase with age was also observed in hypothyroid rats ; however, the magnitude of the increase was significantly reduced. In cerebellum the expression level did not change with age or by thyroid status. In situ hybridization revealed that ZAKI-4 mRNA is widely expressed in neurons throughout the brain. It is noteworthy that the expression in the neurons of layer VI of the cerebral cortex was more evident in control rats than that in hypothyroid rats from
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P17 to P30. Though not influenced by hypothyroidism, there were several regions of the brain in which ZAKI-4 mRNA was strongly expressed. These regions were the mitral cell layer of the olfactory bulb, the substantia nigra, and the hippocampus, where calcineurin is also abundantly expressed. Therefore, it may be hypothesized that ZAKI-4 plays an important role in the development and function of the brain by modulating calcineurin function; and decrease in ZAKI-4 mRNA expression in the specific brain areas may explain, in some parts, the mechanism of abnormal brain development by hypothyroidism.
There are two isoforms of mRNAs, α and β, in ZAKI-4. These isoforms differ at the 5' region but are the same in the rest of the sequences. Expressions of ZAKI-4 a and /3 mRNAs show a distinctive tissue distribution in the mouse, suggesting their specific functions in each tissue. ZAKI-4 α and β mRNAs encode 192 and 243 amino acids, respectively. The sequences differ at their N-terminal regions but are completely identical at the C-terminal region, which includes an calcineurin-inhibitory motif. In mouse, expressions of ZAKI-4 α and β show distinct tissue distribution. While ZAKI-4 α mRNA is expressed specifically in brain, ZAKI-4 ft mRNA is expressed not only in brain but also in other tissues such as heart and skeletal muscle. Al, though both isoforms seem to function as a calcineurin inhibitor, the difference in their N terminal regions and their distinct distributions suggest that ZAKI-4 α and βp exert biological functions in a tissue specific manner in vivo. Less
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