Genetic control of endogenous C-type virus production in pancreatic acinar cells of C57BL/He and C57BL/6J mice.

Abstract

Electron microscopy revealed very active production of C-type virus particles in the pancreatic acinar cells of untreated normal adult mice of the C57BL/ He strain. In C57BL/6J mice, a similar picture was observed after a single intraperitoneal injection of dexamethasone. No viruses were observed in the pancreas of untreated or dexamethasone-treated BALJ3/c and C3Hf mice. F1 hybrids of both C57BL strains with C3Hf mice produced viruses in the same manner and quantity as the C57BL parents, whereas hybrids with BALB/c mice were entirely negative. Approximately 50% of mice of the first backeross generation of (BALB/c X C57BL/He)Fl hybrids with C57BL/He mice were active producers of C-type particles, while the other 50% were negative. It is suggested that a regulator gene that controls C-type virus production does not function in the pancreatic cells of either C57BL strain, and that BALB/c mice can provide hybrids with an active regulator.Recent developments of genetic studies on murine leukemia virus have been promoted by the possibility of detecting viral antigens and RNA-dependent DNA polymerase (reverse transcriptase) as markers for the presence and expression of viral information inserted in the cell genome. The findings that halogenated thymidine analogs and glucocorticoid hormones can, respectively, induce and stimulate cell lines to synthesize viral antigens and particles with great efficiency have further facilitated these studies (1, 2).The detection of C-type particles by electron microscopy can also contribute, provided that a sustained virus production takes place in the tissues under study. We have recently demonstrated by electron microscopy an intense proliferation of C-type virus in the pancreatic acinar cells of normal untreated adult mice of the low-leukemia C57BL/He strain (3). In this paper we report that C57BL/6J mice, generally considered virus-free, also present the same phenomenon after treatment by dexamethasone, whereas, this was not the case with BALB/c and C3Hf mice. In They were dehydrated in graded ethanol and embedded in Epon-Araldite mixture. Ultrathin sections stained with uranyl acetate and lead citrate were mounted on 300 mesh copper grids. They were examined in a Philips EM-300 electron microscope at 60 kV. RESULTSThe data on a semiquantitative evaluation of extracellular C-type particles produced by the exocrine pancreas of untreated or dexamethasone-treated mice of different strains are shown in Table 1. The acinar cells of untreated C57BL/He were found to contain, as previously reported (3), a large number of C particles in cytoplasmic vacuoles and in dilated cisternae of the endoplasmic reticulum, whereas only a small number of extracellular particles was seen. In contrast, the pancreas of untreated C57BL/6J mice presented no intracellular particles and only a few particles in the extracellular spaces. Dexamethasone treatment of C57BL/He mice resulted in a large increase of the extracellular C-type particles, mostly mature (Fig. 1). The dexamethasone-treated C57BL/ ...

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“…Type C viral information has been detected in the genomes of all mouse strains examined, and exocrine pancreatic cells of some, but not all, inbred mouse strains have been shown to be a favoured site for type C-particle replication [4]. The lack of endogenous type C viral enzyme activity in any of the density gradient peak fractious from isolates from BL/Ks normal and db/db pancreases (Figs.…”

An experimental geneticist looks at catecholamine metabolism

“…Studies on F1 and backcross hybrids suggest that even characteristics like the output of steroids by cells in vitro can be influenced by maternal differences, at least in the case of C57BL and DBA mice (Wood & Shire 1980). Such maternal effects could have consequences for the stress responses (Treiman et al 1970) and susceptibility to viruses and other pathogens (Boiocchi et al 1975) of the offspring, even when these had, as in the case of F1 females, identical nuclear genomes.…”