Expression and localization of hsp-23 in unstressed and heat-shocked Drosophila cultured cells

The cellular distribution and expression of hsp-23 in Drosophila Kc cultured cells was studied by indirect immunofluorescence. In unstressed cells, hsp-23 is only expressed in less than 5% of the cellular population and shows an exclusive cytoplasmic localization. Following heat shock, the 23-kilodalton (kDa) heat-shock protein (HSP) is present in all cells; it can be found both in the nucleolus and in granules in the cytoplasm. After 3 h of recovery at 23 °C, the 23-kDa HSP returns to the cytoplasm where it shows a diffuse distribution. Thus the previously reported low amounts of the 23-kDa HSP in unstressed cells does not seem to represent a basal level of expression in every cell but rather selective expression in certain cells.