A histological processing technique that preserves the integrity of calcified tissues (bone, enamel), yolky amphibian embryos, and growth factor antigens in skeletal tissue

We have devised a processing technique to embed calcified tissues, such as bone and tooth enamel, in paraffin, to preserve the delicate antigenic sites of molecules such as growth factors. The same technique, omitting the decalcification step, allows delicate tissues, such as axolotl embryos (Ambystoma mexicanum) containing large yolk masses, to be easily handled during tissue processing and to be serially sectioned. Specimens were all fixed in periodate-lysine-paraformaldehyde (PLP) fixative at 5 degrees C. Bone and teeth were decalcified in an EDTA-G solution at -4 degrees C. Maintaining a temperature of 5 degrees C, the decalcified samples were then washed (with PBS, pH 7.2, under vacuum) to remove glycerol. Both the decalcified tissues and the yolky embryos were dehydrated through an ascending series of isopropanol and embedded in low melting-point paraffin under vacuum. Acidic fibroblast growth factor (aFGF) was located in cells of the expanded cambial layer in the early fracture calluses of male CD-1 mice, demonstrating retention of antigenic sites. The results reported here have not previously been obtained with existing processing and embedding techniques.