Firefly luciferase circRNA-LNP

Luciferin reporter gene assay is a reporting system to detect the activity of Firefly Luciferase using luciferin as a substrate, which is often used in the research of miRNA target gene verification and promoter transcriptive activity regulation. Dual luciferase usually refers to Firefly luciferase and Renilla luciferase.

Cytotoxicity assays are usually based on the assessment of cell membrane damage, which can also be indirectly detected by measuring cell viability. Detection methods include MTT assay, CKK-8 assay, LDH assay and ATP assay, etc.

Live/dead viability and cytotoxicity staining assays are based on the simultaneous detection of intracellular esterase activity in metabolically active (viable) cells and membrane integrity loss in non-viable cells. In commonly used dual-staining approaches, membrane-permeant fluorogenic substrates are converted by intracellular esterases into fluorescent products in live cells, while impermeant DNA-binding dyes selectively enter cells with compromised plasma membranes and label nucleic acids in dead or dying cells, enabling discrimination between viable and non-viable populations by fluorescence microscopy or flow cytometry.

The CCK-8/WST-8 assay is based on the reduction of the water-soluble tetrazolium salt WST-8 to a water-soluble formazan product by cellular dehydrogenases in metabolically active cells, where the generated formazan amount is proportional to the number of living cells and is quantified by measuring absorbance in the visible range, providing a colorimetric readout for cell viability and proliferation assessment. This class of tetrazolium-based assays improves upon earlier MTT-based systems by producing a water-soluble formazan, eliminating the need for organic solubilization steps and enabling direct spectrophotometric measurement in culture medium.

The MTT assay is a colorimetric endpoint assay for estimating viable cell number, cell growth, cytotoxicity, or cell activation in cultured mammalian cells. Living cells reduce the yellow tetrazolium salt MTT into purple/blue formazan, while dead cells do not generate the same signal; the resulting color can be quantified with a multiwell spectrophotometer. MTT reduction is commonly interpreted as a readout of metabolic activity that often correlates with viable cell number, but it should not be treated as a direct cell-counting method unless the assay is optimized for the cell type and experimental condition. Studies show that MTT reduction can involve mitochondrial and non-mitochondrial reducing systems, and formazan may accumulate in intracellular lipid droplets rather than simply marking mitochondria.

CRISPRi and CRISPRa use catalytically inactive Cas9, typically SpCas9 D10A/H840A, as an RNA-guided DNA-binding platform that targets genomic loci through sgRNA complementarity and an adjacent PAM without generating Cas9 nuclease-mediated DNA cleavage. CRISPRi represses transcription by recruiting dCas9 alone or dCas9 fused to repressor domains such as KRAB to promoters or transcription start site regions, while CRISPRa activates transcription by recruiting activation domains such as VP64, VPR, or SAM components to promoter-proximal regions. The primary readout is target-gene expression change, commonly measured by RT-qPCR, RNA-seq, reporter fluorescence, or protein-level assays, and the readout reflects transcriptional repression or activation at the targeted endogenous locus.

The following protocol uses the MTT colorimetric assay as a classic literature-established method for assessing cell viability/metabolic activity in cultured mammalian cells. MTT[3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide] is reduced by metabolically active cells to a colored formazan product; the amount of formazan is quantified spectrophotometrically and provides an indirect measure of metabolically active viable cells. Importantly, MTT reduction reflects cellular oxidoreductase/metabolic activity rather than an absolute direct count of living cells, so changes in cellular metabolism can alter the signal independently of cell number.