As discussed previously (13), there are several different techniques for injecting RNA into Xenopus eggs, and it is not possible to describe them all. We therefore describe the methods used in our own laboratory.
1. Microinjection needles are prepared from capillary tubing, such as GC120F-15 made by Clark Electromedical Instruments (Reading, England). We have used two types of needle puller. One consists of nothing more than a heated platinum coil. The capillary is clamped at its top, passed down through the coil, and a piece of modeling clay (about 7 g) is attached to the bottom. The current is then switched on. The shape of the needle and the diameter of the tip depend on the amount of current passed through the coil, the exact weight of the modeling clay, and on whether the investigator is able to catch the tubing before it hits the bench.
The second option is to use more expensive pullers, such as those made by Campden Instruments or Kopf. Whatever kind of puller is used, the diameter of the needle tip should not exceed 15 |im. Needles should be heated to 180°C to destroy RNAase activity, and they should be stored in a dust-free atmosphere.
2. Singer Instrument Company Micromanipulator, Mark I.
3. Inject + Matic air-driven injector (Supplied by Micro Instruments Ltd., Long Hanborough, Oxford, UK).
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