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 Müller glial cells of intact embryonic chicken retina with that of primary cultures derived from Müller 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 contransfection of Müller cell primary cultures. The progesterone receptor (PR) was also demonstrated to function in intact retina, but not in Müller cell primary cultures. An immunochemical assay was utilized to confirm that a glucocorticoid-responsive, beta-galactosidase-encoding fusion gene was specifically induced in Müller cells after its transfection into intact retina. Thus, in contrast to Müller cells in intact retina, Müller 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 Müller glial cells.