Differential LHRH secretion, dye coupling, and protein expression in two morphologically distinct cell types...

The immortalized neuronal cell line, GT1-7, has been shown to secrete LHRH in a pulsatile manner and to possess many other characteristics of hypothalamic LHRH neurons in vivo, and thus provides a potential model system for studying biochemical and physiological mechanisms regulating LHRH secretion. In the present study, two morphologically and functionally distinct types of cells have been identified in GT1-7 cultures and each type purified to over 95% homogeneity. One type (N cells) appeared more neuronal with extended neurites and somewhat rounded cell perikarya, while the other type (G cells) had flatter cell perikarya that contained filopodia but no neurites. Growth properties of the two cell types also differed. The doubling time for proliferation of N cells was nearly two-fold shorter than that for G cells and N cells displayed 'piling up' whereas G cells exhibited contact inhibition. Functionally, N cells, but not G cells, were dye-coupled as measured by a fluorescence photobleaching assay. While both cell types expressed LHRH, N cells released significantly higher levels of LHRH into the culture media and exhibited more intense LHRH immunostaining. The two cell types also showed differences in immunostaining for other proteins. N cells, unlike G cells, immunostained positive for neuron-specific enolase (NSE), whereas G cells, unlike N cells, stained immunopositive for vimentin. Both cell types expressed SV-40 T antigen protein, indicating that they were derived from the same transgenic mouse hypothalamic tumour. The physiological significance of these two cell types in GT1-7 cultures remains to be determined, but elucidation of their morphological and biochemical properties is intended to contribute to better understanding and application of this experimentally important neuroendocrine cell line.