Making a tooth:growth factors,transcription factors,and stem cells

Mammalian tooth development is largely dependent on sequential and reciprocal epithelial-mesenchymal interactions. These processes involve a series of inductive and permissive interactions that result in the determination, differentiation, and organization of odontogenic tissues. Multiple signaling molecules, including BMPs, FGFs, Shh, and Wnt proteins, have been implicated in mediating these tissue interactions. Transcription factors participate in epithelial-mesenchymal interactions via linking the signaling loops between tissue layers by responding to inductive signals and regulating the expression of other signaling molecules. Adult stem cells are highly plastic and multipotent. These cells including dental pulp stem cells and bone marrow stromal cells could be reprogrammed into odontogenic fate and participated in tooth formation. Recent progress in the studies of molecular basis of tooth development, adult stem cell biology, and regene- ration will provide fundamental knowledge for the realization of human tooth regeneration in the near future.

Inhibition of human La protein by RNA interference downregulates hepatitis B virus mRNA in 2.2.15 cells

AIM: To investigate the role of human La protein in HBV mRNA expression.METHODS: Three human La protein (hLa) specific siRNA expression cassettes (SECs) containing U6+1 promoter were prepared via one-step overlapping extension PCR. After transfection with SECs into HepG2 cells, inhibition effects on hLa expression were analyzed by semi-quantitative RT-PCR and Western blotting. Then, effective SECs were screened out and transfected into 2.2.15 cells, a stable HBV-producing cell line. HBV surface antigen(HBsAg) and e antigen (HBeAg) secretions into culture media were detected by microparticle enzyme immunoassay (MEIA) and HBs and HBe mRNA levels were analyzed by semi-quantitative RT-PCR.RESULTS: SEC products containing U6+1 snRNA promoter,and 3 sites of hLa mRNA specific siRNA were obtained successfully by one-step overlapping extension PCR and could be directly transfected into HepG2 cells, resulting in inhibition of La protein expression in both mRNA and protein levels, among which U6+l-hLa833 was the most efficient,which reduced 18.6-fold mRNA and 89% protein level respectively. In 2.2.15 cells, U6+l-hLa833 was also efficient on inhibition of hLa expression. Furthermore, semi-quantitative RT-PCR showed that HI3s and HBe mRNA levels were significantly decreased by 8-and 66-fold in U6+l-hLa833 transfected cells compared to control. Accordingly, HBsAg and HBeAg secretions were decreased partly posttransfection with SECs.CONCLUSION: PCR-based SECs can be used to mediate RNAi in mammalian cells and provide a novel approach to study the function of La protein. The inhibition of La protein expression can result in a significant decrease ofHBV mRNA, which implies that the hLa protein is also involved HBV RNA metabolism as one of the HBV RNA-stabilizing factors in human cells.

Association between TRAIL expression on peripheral blood lymphocytes and liver damage in chronic hepatitis B

AIM: To explore a novel mechanism for tumor necrosis factorrelated apoptosis-inducing ligand (TRAIL), upregulation of CD4+ and CD8+T lymphocytes participating in the pathophysiological process of chronic hepatitis B (CHB).METHODS: The levels of serum soluble TRAIL (sTRAIL),serum IFN-γ and membrane-bound TRAIL expression on peripheral leucocytes from 58 CHB patients were examined ELISA and flow cytometry respectively. The levels of TRAIL were compared with the baseline levels of 17 healthy controls, and correlation analysis was performed between ALT, TBIL, PT, morphological change in hepatic tissues, and serum IFN-γ.RESULTS: The results showed that TRAIL levels on membranes of CD4+, CD8+ T cells in CHB patients were much higher than those in healthy controls (P＜0.001),and were correlated with serum TBIL (r = 0.354, P = 0.008for CD4+ and r = 0.522, P = 0.000 for CD8+, respectively),ALT (r = 0.393, P = 0.003 for CD8+), PT (r = 0.385,P = 0.004 for CD8+) and serum IFN-γ level (r = 0.302,P = 0.011 for CD4+ and r= 0.307, P = 0.009 for CD8+).On the contrary to membrane-bound TRAIL expression,serum level of sTRAIL was not correlated with that of TBIL and PT, though it was higher than that of the normal population and was positively correlated with serum HBeAg expression (r = 0.695, P = 0.001).CONCLUSION: The expression level of TRAIL on the membrane of lymphocytes was upregulated and associated with the liver injury in CHB patients. These findings suggest that upregulation of TRAIL expression may be induced by virus antigen and inflammatory cytokine IFN-γ.