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爪蟾蝌蚪全脑电转染方法Whole-brain electroporation in Xenopus tadpoles

实验技术Protocol

1. 技术原理Principle

全脑电穿孔通过高压电场瞬时改变细胞膜通透性，实现质粒 DNA 等大分子在蝌蚪全脑或特定脑区的高效转染。定向施加电场可靶向单侧或双侧视顶盖、端脑等区域，适用于神经发育与脑功能的在体研究。适用发育期：NF 42–48 期。Whole-brain electroporation uses a pulsed high-voltage electric field to transiently permeabilise cell membranes, enabling efficient delivery of plasmid DNA into the entire tadpole brain or defined brain regions. Directional field application targets unilateral or bilateral optic tectum, telencephalon, etc. Target stage: NF 42–48.

爪蟾蝌蚪全脑电转染关键步骤示意图
图：全脑电转染关键步骤。（A）脑室注射电极放置；（B）单侧靶向；（C）单侧视顶盖有效转染 GFP；（D）双侧靶向；（E）全脑 GFP 表达。Fig: Key steps. (A) Electrode placement for ventricular injection; (B) unilateral targeting; (C) efficient GFP transfection in unilateral tectum; (D) bilateral targeting; (E) whole-brain GFP expression.

2. 主要设备与耗材Equipment & materials

设备 / 耗材Item型号 / 规格Spec / model关键参数Key parameter
显微操作系统MicromanipulatorSutter MP-285三维精度 ±0.1 μm3D precision ±0.1 μm
电脉冲发生器StimulatorGrass SD90–100 V, 脉冲宽度 0.1–100 ms
微压力注射仪Pressure injectorPicospritzer III最小注射量 10 nLMin. injection 10 nL
玻璃微电极Glass micropipette硼硅酸盐, 1.0 mm ODBorosilicate, 1.0 mm OD尖端 15 μmTip 15 μm
铂电极Platinum electrode定制 1×2 mm 铂片Custom 1×2 mm Pt pad间距 1.5–2.0 mmSpacing 1.5–2.0 mm
解剖显微镜Dissecting scopeLeica M808–40×, LED

3. 实验准备Preparation

DNA 工作液配制DNA working solution

成分Component浓度Concentration说明Note
质粒 DNA（超纯）Plasmid DNA (endotoxin-free)0.2–2.0 μg/μLA260/A280 = 1.8–2.0
Fast Green0.01% (w/v)注射定位指示剂Injection visualisation
2 mM CaCl₂稀释至终体积q.s.增强 DNA 吸附Improve DNA adsorption

工作液分装 −20 ℃ 避光保存，避免反复冻融（≤3 次）。Aliquot and store at −20 ℃ protected from light; ≤3 freeze-thaw cycles.

动物预处理Animal preparation

  • 麻醉：0.02% MS-222（pH 7.4）浸泡 5–7 min 至翻正反射消失。Anaesthesia: 0.02% MS-222 (pH 7.4) for 5–7 min until righting reflex disappears.
  • 固定体位：将蝌蚪置于湿润 Kimwipe 上，背面朝上，充分暴露头部。Position: place tadpole dorsal-side up on a moist Kimwipe, exposing the head.

4. 操作流程Procedure

脑室 DNA 注射Ventricular DNA injection

  • 微电极拉制参数：P-87, Heat=580, Pull=100, Vel=60，尖端直径约 15 μm。Puller settings: P-87, Heat=580, Pull=100, Vel=60; tip diameter ~15 μm.
  • 注射压力 10–15 psi；单次注射量 75–125 nL（全脑覆盖 ~100 nL，局部靶向 ~50 nL）。Injection pressure 10–15 psi; volume 75–125 nL per injection (whole-brain: ~100 nL; local targeting: ~50 nL).
  • 通过 Fast Green 绿色扩散确认脑室充盈，充盈不足则补注一次。Confirm ventricular filling by Fast Green diffusion; supplement if filling is incomplete.

电穿孔参数Electroporation parameters

参数Parameter标准范围Standard range调整策略Adjustment
电压Voltage30–50 V低电压（30 V）靶向局部；高电压（50 V）全脑30 V for local; 50 V for whole-brain
脉冲数Number of pulses2–7 次每增 1 次脉冲，效率约提升 15%Each additional pulse raises efficiency ~15%
脉冲波形Waveform指数衰减，τ = 70 msExponential decay, τ = 70 ms确保膜电位充分去极化Ensures complete membrane depolarisation

电极放置与极性Electrode placement & polarity

  • 单侧转染：负极靠近目标脑区（DNA 向正极迁移），铂电极间距 1.5 mm。Unilateral: negative pole towards target region (DNA migrates to positive pole); Pt electrode spacing 1.5 mm.
  • 双侧转染：交替切换脉冲极性（需同步触发装置），各侧施加相同脉冲数。Bilateral: alternate pulse polarity (synchronised trigger needed); apply equal pulses to each side.
  • 成功标志：电极接触点产生微气泡；失败标志：大泡沸腾或全身抽搐（应立即降低电压）。Success: micro-bubbles at electrode contact. Failure: boiling bubbles or whole-body convulsion — immediately lower voltage.

术后复苏Recovery

  • 转移至含 0.1× MMR（22 ℃）的复苏槽，10–15 min 内应恢复自主游动；24 h 存活率目标 ≥90%。Transfer to 0.1× MMR (22 ℃) recovery tank; tadpoles should swim spontaneously within 10–15 min. Target 24 h survival rate ≥90%.

5. 质量控制Quality control

  • 转染后 48 h，4% PFA 固定，共聚焦定量 GFP⁺ 细胞密度；双质粒（EGFP:DsRed=1:1）共转染率目标 70±10%。48 h post-EP: fix in 4% PFA, quantify GFP⁺ density by confocal. Dual-plasmid co-transfection rate target 70±10%.
  • H&E 切片评估脑室结构，出血或水肿发生率应 <5%；PI 染色（1 μg/mL）确认细胞死亡率 ≤2%。H&E sections to assess ventricular integrity; haemorrhage/oedema incidence should be <5%. PI staining (1 μg/mL) to confirm ≤2% cell death.

6. 故障排除Troubleshooting

问题Problem可能原因Cause解决方案Solution
无荧光表达No fluorescenceDNA 降解或电极接触不良DNA degraded or poor contact更换新鲜质粒；乙醇清洁铂电极Fresh plasmid; clean Pt electrode with ethanol
脑室出血Ventricular bleeding注射压力过高或穿刺损伤Pressure too high or piercing damage降低注射压力至 8 psi；钝化电极尖端Reduce pressure to 8 psi; blunt electrode tip
术后死亡率 >30%Post-EP mortality >30%电压过载或渗透压失衡Voltage overload or osmolarity imbalance校准脉冲输出；检测溶液渗透压（目标 200–220 mOsm）Calibrate output; check solution osmolarity (target 200–220 mOsm)

操作须遵循动物伦理规范（参照 NIH 实验动物指南第八版），实验方案取得本单位 IACUC 批准。废弃质粒材料高压灭菌（121 ℃, 30 min）后处置；操作后彻底洗手。Comply with institutional IACUC requirements (NIH Guide 8th ed.). Dispose of plasmid waste by autoclaving (121 ℃, 30 min). Wash hands after work.

参考文献References

  1. Haas K, et al. (2002) Targeted electroporation of defined neuronal populations in vivo. Neuron 35(6):1023–1034.
  2. Bestman JE & Cline HT (2008) The RNA-binding protein CPEB controls dendrite morphogenesis and neuronal circuit assembly in vivo. Proc Natl Acad Sci USA 105(51):20494–20499.
  3. Sive HL, Grainger RM, Harland RM (2000) Early Development of Xenopus laevis: A Laboratory Manual. Cold Spring Harbor Laboratory Press.
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