Phase 1: Primary Neuronal Culture Preparation and Transfection — Days 1-7
Isolate primary cortical neurons from E18 Sprague-Dawley rat embryos using standard papain digestion protocol. Plate neurons at 150,000 cells/well in 24-well plates on poly-L-lysine (0.1 mg/ml, Sigma P2636) coated coverslips in Neurobasal medium (Thermo 21103049) with B27 supplement (Thermo 17504044) and 2mM glutamine. Allow neurons to mature for 5 days in vitro (DIV5) before transfection. Design and validate siRNA sequences: Tau siRNA (5'-GCAAGGAGAUUAAGCAGAA-3', Dharmacon), MAP6 siRNA (5'-GGACAUGCUGAACUACUAU-3', Dharmacon), and non-targeting control siRNA (Dharmacon D-001810-10). Perform transfections using Lipofectamine RNAiMAX (Thermo 13778075) at 50nM final concentration for each siRNA.
...Phase 1: Primary Neuronal Culture Preparation and Transfection — Days 1-7
Isolate primary cortical neurons from E18 Sprague-Dawley rat embryos using standard papain digestion protocol. Plate neurons at 150,000 cells/well in 24-well plates on poly-L-lysine (0.1 mg/ml, Sigma P2636) coated coverslips in Neurobasal medium (Thermo 21103049) with B27 supplement (Thermo 17504044) and 2mM glutamine. Allow neurons to mature for 5 days in vitro (DIV5) before transfection. Design and validate siRNA sequences: Tau siRNA (5'-GCAAGGAGAUUAAGCAGAA-3', Dharmacon), MAP6 siRNA (5'-GGACAUGCUGAACUACUAU-3', Dharmacon), and non-targeting control siRNA (Dharmacon D-001810-10). Perform transfections using Lipofectamine RNAiMAX (Thermo 13778075) at 50nM final concentration for each siRNA. Establish four experimental groups (n=6 wells each): control siRNA, tau siRNA alone, MAP6 siRNA alone, and tau+MAP6 co-depletion.
Phase 2: Knockdown Validation and Quality Control — Days 8-10
At 48 hours post-transfection (DIV7), harvest one well from each group for knockdown validation. Extract total RNA using TRIzol reagent (Thermo 15596026) and perform RT-qPCR using TaqMan probes for rat Mapt (Rn00691205_m1), Map6 (Rn01464975_m1), and Gapdh (Rn01775763_g1). Calculate knockdown efficiency using ΔΔCt method with GAPDH normalization. Additionally, perform Western blot validation using anti-tau antibody (Dako A0024, 1:1000) and anti-MAP6 antibody (Novus NBP1-85939, 1:500) with β-actin loading control (Sigma A2228, 1:5000). Only proceed with morphological analysis if knockdown efficiency >70% for both targets.
Phase 3: High-Resolution Morphological Imaging — Days 10-11
At 72 hours post-transfection (DIV8), fix neurons with 4% paraformaldehyde in PBS for 15 minutes at room temperature. Permeabilize with 0.1% Triton X-100 and block with 10% normal goat serum. Perform immunofluorescence staining using mouse anti-MAP2 (Sigma M4403, 1:800) for dendritic morphology and rabbit anti-βIII-tubulin (Abcam ab18207, 1:1000) for overall neuronal structure. Use Alexa Fluor secondary antibodies (Thermo A11001 and A11008, 1:500). Image neurons using confocal microscopy (63x oil objective, 0.3μm z-steps) with identical acquisition settings across all groups. Acquire minimum 25 neurons per condition from 3 independent culture preparations.
Phase 4: Quantitative Morphological Analysis and Microtubule Assessment — Days 11-14
Perform comprehensive morphological analysis using ImageJ and Sholl analysis plugin. Measure primary dendrite number, total dendritic length, dendritic complexity (Sholl intersections), and soma area for each neuron. Additionally, assess microtubule stability using immunofluorescence for acetylated α-tubulin (Sigma T7451, 1:800) as a marker of stable microtubules and tyrosinated α-tubulin (Abcam ab6160, 1:500) for dynamic microtubules. Calculate acetylated/tyrosinated tubulin ratio as an index of microtubule stability. Use live-cell imaging with SiR-tubulin (Cytoskeleton CY-SC002, 100nM) to assess microtubule dynamics in a subset of cultures (n=15 neurons per condition) with 2-minute intervals for 30 minutes.
Phase 5: Statistical Analysis and Data Integration — Days 14-16
Perform power analysis to confirm adequate sample size (β=0.8, α=0.05, expected effect size d=0.8). Use one-way ANOVA followed by Tukey's post-hoc test for multiple comparisons between groups. Apply Bonferroni correction for multiple morphological parameters (adjusted α=0.01). Perform principal component analysis (PCA) to identify patterns in morphological rescue. Calculate rescue index as: [(double depletion value - worst single depletion value) / (control value - worst single depletion value)] × 100%. Statistical analysis using R software with appropriate packages for morphological data analysis.