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Background/Aims: MicroRNA-29b (miR29b) has been previously identified in early mouse embryos through miRNA microarray analysis. Recent research has indicated that miR29b participates in DNA methylation by regulating DNA methyltransferase 3a/3b (Dnmt3a/3b) expression. However, the expression pattern and biological function of miR29b in mouse preimplantation embryonic development remain unknown. Methods: In this study, we examined the expression patterns of miR29b and Dnmt3a/3b in mouse early embryos at different developmental stages. Subsequently, expression and localization of DNMT3A/3B protein was analyzed in mouse early embryos by immunofluorescence staining. The biological function of miR29b in mouse early embryos was analyzed by microinjection of commercially available miRNA-specific inhibitors and mimics. Results: Our data showed that Dnmt3a/3b mRNA expression is negatively regulated by miR29b in mouse early embryos. Immunofluorescence analysis revealed that DNMT3A/3B protein expression is predominantly localized within the nucleoplasm of embryos. Alterations to the activity of miR29b could change the DNA methylation levels in mouse preimplantation embryos and lead to a developmental blockade, from the morula to the blastocyst stage. Conclusion: These results indicated a role for the miR29b-Dnmt3a/3b-DNA methylation axis in mouse early embryonic development, and we provide evidence that miR29b is indispensable for mouse early embryonic development. This study contributes to a preliminary understanding of the role of miR29b during mouse embryonic development.

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Stabilized polyacrylonitrile (PAN) fibers pretreated under N 2 and air atmospheres were prepared and their thermal behaviors were compared by differential scanning calorimetry and thermogravimetry methods. The results indicated that the subsequent stabilization reaction of PAN pretreated in air was more obvious than that in N 2 . In addition, the thermal stability of PAN pretreated in air is better than that in N 2 . The structural analysis by Fourier transform infrared spectroscopy and solid state 13 C nuclear magnetic resonance implied that oxygen promoted dehydrogenation and a compact conjugated structure was formed in PAN. In addition, the C¼ ¼O structures were generated in air and increased gradually with temperature. The contents of oxygen in PAN fibers studied by elemental analysis corresponded with the structural evolution. Further investigation indicated that the C¼ ¼O structures helped dehydration and also promoted formation of the cross-linked structures. A mechanism for structural evolution in PAN during stabilization in air was proposed.

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