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​英訳サンプル:       7​


miR-206 was originally found to be a muscle differentiationspecific miRNA. It was recently discovered that miR-206 was also expressed in osteoblasts, and miR-206 expression decreased with osteoblast differentiation. Overexpression of miR-206 inhibited osteoblast differentiation, and the knockout of miR-206 promoted osteoblast differentiation. Further mechanism studies revealed that the gap junction protein connexin 43 was the target gene of miR-206 in osteoblasts . Transgenic mice expressing miR-206 showed abnormal osteoblast differentiation with a phenotype of low bone mass. These data confirmed that miR-206 was a key negative regulator of osteogenesis, and the regulation of miR-206 determined the fate of osteoblasts.


Runx2 and Smads1/5 are necessary for osteogenic differentiation. miR-133 and miR-135 are down-regulated in the BMP-2-induced pluripotent mesenchymal cell line C2C12. Further, miR-133 is a negative regulator of Runx2. miR-133 directly binds to the predicted binding sequence in the 30 UTR of Runx2 mRNA to inhibit the translation of Runx2 in C2C12 cells. Thus, miR-133 inhibits the osteogenic differentiation of C2C12 that had been induced by BMP-2. Meanwhile, miR-135 represses the osteogenic differentiation of C2C12 cells by targeting the Smad5 gene.


When a cell divides, the genetic material inside that cell needs to be copied. This process is called DNA replication. Watson and Olovnikov proposed that the limitation on cell division is rooted in the very nature of DNA replication. The enzymes that replicate a strand of DNA are unable to continue replicating all the way to the end, which causes the loss of some DNA.




As an analogy, think of a DNA strand as a long row of bricks, and of DNA replication as a bricklayer walking backwards on top of a brick wall laying a new layer on top of that now. When the end of the wall is reached, the bricklayer finds himself standing on top of the brick he is supposed to replicate. Since he can’t put down a brick where his feet are, he steps back and falls off the wall, leaving the very end of the wall bare. As a result, the new copy of the wall is a bit shorter than the original.

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