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How to fix embryos

Fixing embryos refers to preparing the embryo to be ready for molecular techniques such as whole mount RNA in-situ hybridization or for microscopy.  The process of fixing embryos kills the embryo so its cells could be examined.  One needs to take extra caution when dealing with fixative since it is dangerous.

Chemical Safety
Parafomaldehyde is a fixative.  It will fix your tissues just as well as it will fix the sample.  The 4% paraformaldehyde solution can be used only by the course instructors.  It should be disposed of by the instructors in a designated waste container.  Gloves should be worn at all times.

Like with most chemicals, if the chemicals or solutions used in this lab come in contact with your eyes or skin, you should flush the affected area with copious amounts of water, and tell the instructors about the spill.  If a chemical comes in contact with your eyes, or if you have any ill effects from contacting a chemical, you should call a physician. 


1. Place embryos in 4% Paraformaldehyde (PFA) overnight at 4 degree Celsius or 4 hours at room temperature.

2. Dechorionate the embryo and rinse the embryos several times in Phospahte Buffer Saline (PBS).

3. Wash the embryo in 100% Methanol 2 times.  During the second wash, leave the embryo in Methanol for at least 10 minutes at room temperature.

4. Then, put the embryos in fresh Methanol and leave them in -20 degree Celsius for at least 30 minutes.  Basically, leave the embryo in the Methanol until the embryo is needed for a molecular experiment or examination.