Differential expression of gap junctions in neurons and astrocytes derived from P19 embryonal carcinoma cells

The P19 embryonal carcinoma cell line represents a pluripotential stem cell that can differentiate along the neural or muscle cell lineage when exposed to different environments. Exposure to retinoic acid induces P19 cells to differentiate into neurons and astrocytes that express similar developmental markers as their embryonic counterparts. We examined the expression of gap junction genes during differentiation of these stem cells into neurons and astrocytes. Untreated P19 cells express at least two gap junction proteins, connexins 26 and 43. Connexin32 could not be detected in these cells. Treatment for 96 hr with 0.3 mM retinoic acid induced the P19 cells to differentiate first into neurons followed by astrocytes. Retinoic acid produced a decrease in connexin43 mRNA, protein, and functional gap junctions. Connexin26 message was not affected by retinoic acid treatment. The neurons that developed consisted of small round cell bodies extending two to three neurites and expressed MAP2. Connexin26 was detected at sites of cell-cell and cell-neurite contact within 3 days following differentiation with retinoic acid. The astrocytes were examined for production of their intermediate filament marker, glial fibrillary acidic protein (GFAP). GFAP was first detected at 8 days by Western blotting. In culture, astrocytes co-expressed GFAP and connexin43 similar to primary cultures of mouse brain astrocytes. These results suggest that differentiation of neurons and glial cells involves specific connexin expression in each cell type. The P19 cell line will provide a valuable model with which to examine the role gap junctions play during differentiation events of developing neurons and astrocytes.