Stress-responsive genes are lowly transcribed under normal conditions and robustly induced in response to stress. The significant difference between basal and induced transcription indicates that the general transcriptional machinery requires a mechanism to distinguish each transcription state. However, what factors specifically function in basal transcription remains poorly understood. Using a classic model stress-responsive gene (Drosophila MtnA), we found that knockdown of the DEAD-box helicase Hlc resulted in a significant transcription attenuation of MtnA under normal, but not stressed, conditions. Mechanistically, Hlc directly binds to the MtnA locus to maintain the accessibility of chromatin near the transcriptional start site, which allows the recruitment of RNA polymerase II and subsequent MtnA transcription. Using RNA-seq, we then identified plenty of additional stress-responsive genes whose basal transcription was reduced upon knockdown of Hlc. Taken together, these data suggest that Hlc-mediated basal transcription regulation is an essential and widespread mechanism for precise control of stress-responsive genes.
In situ injectable hydrogels, which have great potential in tissue engineering, are characterized by simple preparation, minimal invasiveness and adaptation to complex shapes. However, injectable hydrogels have higher requirements for biocompatibility and safety due to their use in vivo implantation. Therefore, in this study, a human-like collagen (HLC)-based in situ gel-forming injectable HLC-HPA hydrogel was synthesized by combining the amino group of HLC with the carboxyl group of HPA activated using 1-ethyl-3-(3-dimethylaminopropyl)-carbodiimide hydrochloride (EDC) and N-hydroxysuccinimide (NHS), followed by crosslinking by horseradish peroxidase (HRP) and H 2 O 2 , and used as scaffold material for tissue engineering. The hydrogel stiffness, gel time and biodegradation rate could be easily and independently adjusted by varying the H 2 O 2 and HRP concentrations. Scanning electron microscope (SEM) clarified the homogeneous porous and interconnected internal structures of the hydrogel. In vitro cell viability and in vivo degradation experiments confirmed that the HLC-HPA hydrogel had good biodegradability and excellent biocompatibility. Interestingly, in cultured macrophages, the HLC-HPA hydrogel showed anti-inflammatory activity by reducing the amount of the pro-inflammatory cytokines tumor necrosis factor-α (TNF-α) and interleukin- 6 (IL-6) and increasing the secretion of the anti-inflammatory cytokine interleukin-10 (IL-10) induced by lipopolysaccharide (LPS). Meanwhile, in animal experiments, HLC-HPA hydrogels exhibit excellent biocompatibility and have properties of hemostasis and reduction of inflammatory response. Therefore, the HLC-HPA hydrogel prepared in this study has great potential for development for use in the biomedical field.
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