Exploratory experiment designed to discover new patterns targeting MED1, CDK9 in cultured cells and in vitro nucleosome system. Primary outcome: Reduction in DDR foci formation
This experiment examined the role of transcriptional machinery components in DNA damage response (DDR) focus formation through loss-of-function approaches. The researchers used absence or inactivation of key factors (likely RNA polymerase II, MED1, CDK9) and measured the resulting effects on DDR foci formation. The study employed both in vivo cellular systems and an in vitro reconstitution system using nucleosomes to demonstrate that these transcriptional factors are necessary for proper DDR focus assembly. This approach allowed direct testing of whether transcriptional machinery is required for the spatial organization of DNA repair factors into discrete foci.
siRNA Transfection: Design 3 independent siRNAs per target (MED1/CD247, CDK9, and additional DDR factors: ATM, ATR, BRCA1, RNF8). Transfect U2OS at 50% confluence using RNAiMAX (Life Technologies, 30 nM siRNA, 1:1 ratio). Include non-targeting siRNA pool and untreated controls. Validate knockdown via qRT-PCR at 48h and 72h.
Promoter Occupancy: MED1 and CDK9 occupy DDR gene promoters (p21, PUMA, GADD45) at baseline and increase 3-5-fold upon DNA damage. Knockdown reduces promoter occupancy by ≥50%, confirming direct transcriptional regulation.
Focus Phenotype: DDR factor knockdown must produce ≥25% reduction in IR-induced γH2AX or 53BP1 focus count at ≥1 timepoint (6h or 24h post-IR) with statistical significance (p < 0.05, n≥3 independent experiments).
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