E2F coordination of G2/M transcriptional program

PRIMARY OUTCOME

G2/M gene expression levels

EXPECTED OUTCOMES

## Primary Outcomes **E2F Switch**: Endocycling cells show dominant expression of E2F7/E2F8 (repressors) and near-absent E2F1-E2F3 (activators) vs. mitotic cells. This E2F regulatory switch drives endocycle gene expression program. **Target Gene Identification**: E2F7/E2F8 occupy promoters of G2/M genes (Aurora B kinase, PLK1, Cyclin B1) in endocycling cells, repressing their expression by 60-80% vs. mitotic cells. This explains why endocycling cells arrest in G2 without mitosis. ## Secondary Outcomes **Functional Impact**: E2F7 or E2F8 knockdown in endocycling cells causes: (a) reactivation of G2/M gene expression (+40-60% of mitotic levels), (b) appearance of mitotic markers (phospho-H3+ cells), (c) attempted cytokinesis (abnormal multinucleated cells). **Species Conservation**: E2F7/E2F8 binding patterns at G2/M genes are conserved across rat TGCs, human BeWo, and HDF endocycle models, suggesting universal mechanism.

SUCCESS CRITERIA

## Primary Success Criteria **E2F Expression Pattern**: E2F7/E2F8 mRNA must be ≥3-fold higher in endocycling vs. mitotic cells, while E2F1 must be ≤30% of mitotic cell levels (confirmed via qRT-PCR, n≥3). **Target Repression**: G2/M genes (Aurora B, PLK1, CCNB1) must show ≥50% lower expression in endocycling vs. mitotic cells (qRT-PCR, p < 0.01). ## Secondary Success Criteria **ChIP-seq Validation**: E2F7/E2F8 ChIP-seq peaks must be significantly enriched at G2/M gene promoters (≥4-fold over input, q < 0.01) in endocycling cells, confirmed in ≥2 independent ChIP experiments. **Knockdown Rescue**: E2F7 knockdown must reactivate G2/M gene expression by ≥40% and increase phospho-H3+ cells by ≥2-fold, confirming causal relationship.

PROTOCOL

# E2F Coordination of G2/M Transcriptional Program in Endocycling Cells Protocol ## Phase 1: Cell Culture and Synchronization for Endocycle Entry (Days 1-21) **Cell Model**: Use primary rat trophoblast giant cells (TGCs) or human placental BeWo cells as models of physiological endocycle. Alternatively, use serum-starved (48h) Human Dermal Fibroblasts (HDFs) re-entering cell cycle in which E2F7/E2F8 dominate. **Endocycle Induction**: Culture TGCs in DMEM + 10% FBS. Endocycle entry confirmed via: (a) DNA content (4N-8N by propidium iodide, flow cytometry), (b) absence of cytokinesis (cleavage furrow markers absent), (c) upregulation of E2F7/E2F8 (qRT-PCR). **Synchronization**: Harvest asynchronously cycling and endocycling cells at 80% confluence. For cell cycle synchronization in HDFs, perform double thymidine block (2 mM thymidine, 16h each block) to enrich G1/S and G2/M populations. ## Phase 2: E2F Family Expression and Chromatin Binding (Days 22-42) **RNA Extraction and RT-qPCR**: Extract total RNA from endocycling vs. mitotic cells. Synthesize cDNA. Assay E2F transcription factor family (E2F1-E2F8) using SYBR Green qPCR (primer efficiency validated, ΔΔCt method). Include cell cycle markers (CCNA2, CCNB1, CDC2). **Chromatin Immunoprecipitation (ChIP-seq)**: Perform ChIP for E2F7, E2F8, and E2F1 (active form) in endocycling cells using validated antibodies. Cross-link cells (1% formaldehyde), sonicate, immunoprecipitate. Prepare sequencing libraries (10 ng input DNA). Sequence on Illumina NovaSeq (50M reads/sample). **Bioinformatics Analysis**: Map ChIP-seq reads to genome (BWA). Call peaks (MACS2, q < 0.01). Annotate peaks to nearest genes. Perform motif analysis (HOMER) to identify enriched transcription factor motifs. Compare E2F7/E2F8 vs. E2F1 targets. ## Phase 3: Functional Validation of E2F Targets (Days 43-63) **siRNA Knockdown of E2F7/E2F8**: Transfect endocycling cells with siRNAs targeting E2F7 (3 independent siRNAs), E2F8, or both. Knockdown validated via qRT-PCR and western blot (anti-E2F7, #ab235903, anti-E2F8, #ab44566). **Cell Cycle Phenotype**: Assess DNA content (PI staining, flow cytometry) and mitotic markers (phospho-H3 Ser10, western blot) at 72h post-knockdown. Measure G2/M gene expression (Aurora B, PLK1, Cyclin B1) via qRT-PCR. **Direct Target Validation**: For candidate G2/M genes, perform ChIP-qPCR for E2F7/E2F8 binding at promoter regions. Use primers flanking E2F consensus sites. Compare enrichment over IgG control.

LINKED HYPOTHESES

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[E2F coordination of G2/M transcriptional program](http://scidex.ai/artifact/exp-6a6ceb54-5493-433f-bfc7-00e34451cc09)

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