1994 Fiscal Year Final Research Report Summary
Regulation of the expression of microvillar lactase in small intestine
| Project/Area Number |
05670071
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| Research Category |
Grant-in-Aid for General Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Research Field |
Environmental physiology (including Physical medicine and Nutritional physiology)
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| Research Institution | University of Shizuoka |
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Principal Investigator |
GODA Toshinao University of Shizuoka, School of Food and Nutritional Sciences, Department of Nutrition, Instructor, 食品栄養科学部・栄養学科, 助手 (70195923)
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| Co-Investigator(Kenkyū-buntansha) |
TAKASE Sachiko University of Shizuoka, School of Food and Nutritional Sciences, Department of N, 食品栄養科学部・栄養学科, 教授 (10046196)
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| Project Period (FY) |
1993 – 1994
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| Keywords | Lactase / Sucrase / mRNA / Microvillar Membrane / Carbohydrate / Lipid / Diurnal Rhythm / Intestinal Villus |
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| Research Abstract |
Regulatory mechanisms of lactase expression were investigated.
1.Gene expression of lactase along the villus-crypt axis :
Dot blot hybridization of lactase mRNA extracted from six consecutive fractions of villus-crypt columns revealed that, unlike sucrase mRNA which was expressed maximally in the lower villus, maximal lactase mRNA level was not attained until the upper villus, suggesting that lactase gene is continuously expressed in the differentiating as well as in the mature absorptive cells.
2.Dietary regulation of lactase gene expression :
A short-term force-feeding experiment showed that sucrese evoked lactase mRNA levels, but a non-metabolizable sugar (alpha-methylglucoside) was unable to enhance it.The sucrose-induced increase in lactase mRNA levels was observed along the entire height of villi, and this enhancement was completely inhibited by actinomycin D injection, suggesting that lactase gene transcription might be enhanced by metabolite (s) of carbohydrates.
3.Localization of l
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actase in enterocytes :
Immunoelectron microscopy revealed that lactase was detected not only in the microvilli, but also in the lateral membranes, suggesting that an alternative route for intracellular transport of lactase via the lateral membranes to the microvilli.
4.Diet-induced changes in posttranslational modifications of lactase :
Feeding medium-chain triglycerides (MCT) causes a decrease in bile acid concentrations in the intestinal lumen, resulting in a retarded degradation of sucrase in the microvilli.The animals fed the high long-chain triglyceride (LCT) diet showed a lower lactase activity than the rats fed the high-MCT diet, which was accompanied by the reduction in the lactase activity per unit weight of immunoreactive lactase, suggesting that LCT might accelerate inactivation and/or degradation of lactase.
5.Diurnal rhythm of lactase expression :
Sucrase mRNA exhibited diurnal variations, but lactase mRNA did not show diurnal variations.Total lactase activity in the microvillar membranes showed a diurnal variation together with a parallel variation of total microvillar proteins, suggesting that diurnal rhythm of lactase activity is caused by a change in turnover of microvillar proteins. Less
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