Improvements in histological quality and signal retention following in situ hybridization in early chick embryos using plastic resin and recolorization.

We describe a novel method that allows reliable detection of in situ hybridization signals in thin sections of plastic embedded embryos. Sections from plastic embedded embryos are thinner and have superior histological quality compared to paraffin, gelatin, agarose embedded sections or cryosections; however, plastic resin traditionally has not been used as an embedding medium following in situ hybridization because of loss of signal. When signal is detected with alkaline phosphatase and NBT/BCIP, the resulting colored precipitate is subject to fading when samples are exposed to organic compounds. The colored precipitate can be redeposited by repeating the NBT/BCIP reaction following plastic sectioning. This recolorization shows no loss of specificity, because signal is detected only where the anti-digoxigenin/alkaline phosphatase conjugated antibody is bound to the riboprobe. Strong signals can be detected without recolorization; however, weaker signals require the recolorization step. This novel method of re-depositing colored precipitate after processing and sectioning allows accurate determination of the location of gene expression and study of this expression in high quality histological sections of early chick embryos.