Hemi-methylated CpG sites connect Dnmt1-knockdown-induced and Tet1-induced DNA demethylation during somatic cell reprogramming.

The relationship between active DNA demethylation induced by overexpressing Tet1 and passive DNA demethylation induced by suppressing Dnmt1 remains unclear. Here, we found that DNMT1 preferentially methylated, but TET1 preferentially demethylated, hemi-methylated CpG sites. These phenomena resulted in a significant overlap in the targets of these two types of DNA demethylation and the counteractions of Dnmt1 and Tet1 during somatic cell reprogramming. Since the hemi-methylated CpG sites generated during cell proliferation were enriched at core pluripotency loci, DNA demethylation induced by Tet1 or sh-RNA against Dnmt1 (sh-Dnmt1) was enriched in these loci, which, in combination with Yamanaka factors, led to the up-regulation of these genes and promoted somatic cell reprogramming. In addition, since sh-Dnmt1 induces DNA demethylation by impairing the further methylation of hemi-methylated CpG sites generated during cell proliferation, while Tet1 induced DNA demethylation by demethylating these hemi-methylated CpG sites, Tet1-induced DNA demethylation, compared with sh-Dnmt1-induced DNA demethylation, exhibited a higher ability to open the chromatin structure and up-regulate gene expression. Thus, Tet1-induced but not sh-Dnmt1-induced DNA demethylation led to the up-regulation of an additional set of genes that can promote the epithelial-mesenchymal transition and impair reprogramming. When vitamin C was used to further increase the demethylation ability of TET1 during reprogramming, Tet1 induced a larger up-regulation of these genes and significantly impaired reprogramming. Therefore, the current studies provide additional information regarding DNA demethylation during somatic cell reprogramming.

Overproduction of α-Lipoic Acid by Gene Manipulated Escherichia coli.

Alpha-lipoic acid (LA) is an important enzyme cofactor widely used by organisms and is also a natural antioxidant for the treatment of pathologies driven by low levels of endogenous antioxidants. In order to establish a safer and more efficient process for LA production, we developed a new biological method for LA synthesis based on the emerging knowledge of lipoic acid biosynthesis. We first cloned the lipD gene, which encodes the lipoyl domain of the E2 subunit of pyruvate dehydrogenase, allowing high levels of LipD production. Plasmids containing genes for the biosynthesis of LA were subsequently constructed utilizing various vectors and promotors to produce high levels of LA. These plasmids were transformed into the Escherichia coli strain BL21. Octanoic acid (OA) was used as the substrate for LA synthesis. One transformant, YS61, which carried lipD, lplA, and lipA, produced LA at levels over 200-fold greater than the wild-type strain, showing that LA could be produced efficiently in E. coli using genetic engineering methods.