| Research Abstract |
In the present project, the following findings were made.
1) The long terminal repeat (LTR) of endogenous mouse mammary tumor virus (MMTV) in the SHN mouse strain, known to have a high incidence of mammary tumors, was cloned and its sequence was elucidated. In the open reading frame between 280 and 380 codons, many base changes were found when compared with reported murine MMTV sequences. In contrast, the sequence of regulatory area of the present LTR was well preserved.
2) The MMTV DNA was found to exist as extrachromosomal DNA fragments in the skin and was proven that it is an entire whole MMTV genome. Its role in the MMTV replicating processes, however, remains unknown.
3) It has been known that energy restriction (ER) suppresses gene expression of MMTV, although its mechanisms still remains unknown. We found that ER induced torpor and it, in turn, suppressed cellular proliferation in various organs. Suppression, however, was alleviated by increases in energy consumption or in housing temperatures.
4) We found that ER decreased the total amount of RNA specifically as well as numbers of cells. PRL mRNA was, however, decreased by ER to much greater extent than that in actin mRNA, suggesting that PRL mRNA decreased more profoundly than other genes.
5) Activities of microsomal Aa^<++>-ATPase was found to be decreased after ER.Their activities were found to be decreased at euthermic body temperatures in brain, liver, and salivary glands, and in these and kidney at heterothermic body temperatures.
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