Optimization of in situ hybridization histochemistry for localization of GAP-43 mRNA in fetal brain during human...

In situ hybridization histochemistry has proven to be an important tool for cellular and molecular studies in neurobiology. The method basically involves the anatomic localization of labeled RNA or DNA molecules that hybridize with complementary target RNA or DNA sequence in the cell. In regard to gene expression, in situ hybridization allows the study of specific mRNA level and distribution between various cell types, or of comparative levels of mRNA throughout development. Major advantages of in situ hybridization are: (a) specific mRNAs can be detected in heterogeneous cell populations where only one of multiple sets of cells present may be transcribing the mRNA of interest; (b) it allows the maximal use of rare tissues that may be in short supply (clinical biopsies, embryos, cultured cells); (c) the location of the mRNA can be identified on conventional microscopic sections without the necessity of electron microscopy; and (d) identification of specific gene without metabolic incorporation of radiolabeled precursor into the endogenous protein in the cells. Because of these advantages, we decided to utilize this approach for specific studies involving the expression and distribution of GAP-43 (growth-associated protein 43) mRNA in early human development. The method we employed for in situ hybridization is basically a modification of the many original protocols developed by others and can be easily applied to many studies of cellular gene expression in the human nervous system.