EXPRESSION OF THE GENES-CODING FOR GLUTAMIC-ACID DECARBOXYLASE IN PLURIPOTENT CELL-LINES

The expression of glutamic acid decarboxylase (GAD) is a basic characteristic of a wide array of inhibitory neurons that use gamma-aminobutyric acid as a neurotransmitter. Clonal cell models will be essential for investigating the mechanisms which are responsible for the selective expression of GAD. P19 embryonal carcinoma cells are an important model for the analysis of neuronal gene expression. Depending on culture conditions, undifferentiated cells can be induced to form cells as widely divergent as cardiac muscle-like cells and neuron-like and glial-like cells. P19 cells are amenable to a number of powerful genetic manipulations including transformation with foreign DNA and selection of mutants. In this study we used nuclease protection assays and Northern blot analysis to determine if P19 cells express the GAD1 and GAD2 genes. The results show that uninduced P19 cells express these genes at very low but easily detectable levels. When the cells are induced to differentiate along the neuronal pathway with retinoic acid, the levels of transcripts for both GAD genes rise dramatically. At least some RNA transcripts of both genes from induced cells comigrate with the corresponding mRNA from the brain and thus probably represent processed mRNA. The expression of GAD genes in undifferentiated cultures of embryonal stem (ES) cells was also investigated. These cultures express levels of GAD1 transcripts that are higher than uninduced P19 cells. In contrast, expression of the GAD2 gene was barely detectable. These results indicate that P19 EC cells and ES cells will be useful for the investigation of the mechanisms that regulate the expression of the GAD1 and GAD2 genes.