DIFFERENTIAL LHRH SECRETION, DYE-COUPLING, AND PROTEIN EXPRESSION IN 2 MORPHOLOGICALLY DISTINCT CELL-TYPES IDENTIFIED IN GT1-7 CULTURES

The immortalized neuronal cell line, GT1-7, has been shown to secrete LHRH in a pulsatile manner and to possess many other characteristics o f hypothalamic LHRH neurons in vivo, and thus provides a potential mod el system for studying biochemical and physiological mechanisms regula ting LHRH secretion, In the present study, two morphologically and fun ctionally distinct types of cells have been identified in GT1-7 cultur es and each type purified to over 95% homogeneity, One type (N cells) appeared more neuronal with extended neurites and somewhat rounded cel l perikarya, while the other type (G cells) had flatter cell perikarya that contained filopodia but no neurites, Growth properties of the tw o cell types also differed, The doubling time for proliferation of N c ells was nearly two-fold shorter than that for G cells and N cells dis played 'piling up' whereas G cells exhibited contact inhibition, Funct ionally, N cells, but not G cells, were dye-coupled as measured by a f luorescence photobleaching assay, While both cell types expressed LHRH , N cells released significantly higher levels of LHRH into the cultur e media and exhibited more intense LHRH immunostaining. The two cell t ypes also showed differences in immunostaining for other proteins. N c ells, unlike G cells, immunostained positive for neuron-specific enola se (NSE), whereas G cells, unlike N cells, stained immunopositive for vimentin, Both cell types expressed SV-40 T antigen protein, indicatin g that they were derived from the same transgenic mouse hypothalamic t umour, The physiological significance of these two cell types in GT1-7 cultures remains to be determined, but elucidation of their morpholog ical and biochemical properties is intended to contribute to better un derstanding and application of this experimentally important neuroendo crine cell line.