Immunofluorescence analysis of the time-course of extinction, reexpression, and activation of albumin production in rat hepatoma-mouse fibroblast heterokaryons and hybrids.

Abstract

We have used a combination of a sensitive immunocytochemical stain for intracellular albumin, and Hoechst 33258 dye for identification of parental nuclei to investigate the time-course of extinction, reexpression, and activation of albumin production in fusion products of 1s (hyperdiploid) or 2s (hype rtetradiploid) rat hepatoma cells with mouse fibroblasts (L cells or embryonic cells) . In all combinations, the initial event is extinction of albumin production . Extinction occurs immediately after fusion when the mouse fibroblast is a normal embryonic (senescent?) cell . In the case of an L cell, rat albumin is synthesized and secreted during the first 12 h after fusion ; no production of mouse albumin occurs . Thereafter, albumin production ceases . 8-12 d after fusion, young hybrid colonies are found to resume the synthesis of rat albumin (reexpression), and several days later the production of mouse albumin begins (activation) . The patterns of reexpression and activation indicate (a) that chromosome loss is not necessary for either event to occur and (b) that the cells active in the synthesis of mouse albumin are a subpopulation of those cells already engaged in the production of rat albumin. We conclude that (a) extinction is mediated by diffusible factor(s) from the L-cell parent that act in the hepatoma nucleus to prevent the formation of new albumin messenger RNA; (b) reexpression and activation are gene dosage-dependent but extinction is not; and (c) previously active genes are more rapidly expressed than previously silent ones .

Neuroblastoma × spinal cord (NSC) hybrid cell lines resemble developing motor neurons

“…Thus, it appears that amplified N-myc in neuronal hybrids can not only serve to immortalize the hybrids, but may also not suppress expression of neuronal differentiated properties. Since the neural crestdescended neuroblastoma fusion partner is derived from the same embryonic primordium as neural tubedescended central neurons, it would also be expected that tissue extinction factors, initially described in fusion of cells from widely differing tissues (Mavel-Ninio and Weiss, 1981;Killary and Fournier, 1984), would be less likely to pertain to the NSC fusion series.…”

Lack of retrovirus gene expression in somatic cell hybrids of friend cells and teratocarcinoma cells with a teratocarcinoma phenotype.

“…Diffusible products of viral origin are probably not responsible for this regulation, because mutant polyoma viruses cannot complement wild-type virus functions (7). Kahn et al (17) have presented evidence for a cytoplasmic, diffusible substance to cause extinction of one differentiated phenotype in hybrid cells (24). It would now-be of major interest to determine whether the same factor is also involved in the extinction shown by teratocarcinoma phenotype hybrids or their differentiated progeny.…”

A liver-specific factor essential for albumin transcription differs between differentiated and dedifferentiated rat hepatoma cells.

“…In other words is vAPF itself an extinguishing protein? Extinction of albumin expression as well as other liver functions has been observed upon fusion of differentiated hepatoma cells with dedifferentiated variants or fibroblasts (Mevel-Ninio and Weiss 1981;Ott et al 1984a). Moreover, the selective extinction of albumin is directly related to the presence of a single chromosome and appears to act on or via the 5'-flanking albumin promoter sequences (Petit et al 1986).…”