Steroid hormone receptors activate transcription in glial cells of intact retina but not in primary cultures of retinal glial cells

We have compared the steroid responsiveness of Muller glial cells of intact embryonic chicken retina with that of primary cultures derived from Muller glia. Appropriately constructed fusion genes were found to be highly glucocorticoid inducible after their cotransfection with an expression vector encoding the human glucocorticoid receptor (GR) into intact embryonic d 10 (E10) or E5.5 retina. Dramatically attenuated inductions were obtained after cotransfection of Muller cell primary cultures. The progesterone receptor (PR) was also demonstrated to function in intact retina, but not in Muller cell primary cultures. An immunochemical assay was utilized to confirm that a glucocorticoid-responsive, beta-galactosidase-encoding fusion gene was specifically induced in Muller cells after its transfection into intact retina. Thus, in contrast to Muller cells in intact retina, Muller cells in primary culture have lost the capacity to achieve transcriptional activation by steroid receptors. We postulate that coordinate expression of the GR, and other more general factors required for steroid inducibility, is lost by dispersion and primary culture of retinal Muller glial cells.