Synthesis of mitochondrial RNA in hamster-mouse hybrid cells

Mitochondrial protein synthesis in interspecific somatic cell hybrids

The fusion of an oligomycin (OLI)-resistant mutant of mouse LM(TK-) cells to a chloramphenicol (CAP)-resistant mutant of AK412 Chinese hamster cells resulted in a series of interspecific somatic cell hybrids. Hybrids selected in HAT medium retained only mouse mitochondrial genomes while hybrids selected in HAT plus CAP and OLI retained both hamster and mouse mitochondrial genomes in approximately equal amounts. Nuclear-coded mitochondrial proteins from both parental species were incorporated into mitochondria in all of the hybrids. However, the mitochondrially coded proteins of three individually isolated hybrid cell lines were predominantly mouse-specific, with only trace amounts of hamster protein detected.

Retention of both parental mitochondrial DNA species in mouse-Chinese hamster somatic cell hybrids

Interspecific somatic cell hybrids were isolated following the fusion of an oligomycin-resistant derivative of LM (TK-) mouse cells to a chloramphenicol-resistant derivative of AK412 Chinese hamsters cells. Hybrids were selected in either HAT medium, HAT plus chloramphenicol (CAP), HAT plus oligomycin (OLI), or HAT plus chloramphenicol and oligomycin. Cytogenetic analysis of the hybrids indicated that their karyotype reflected the sum of the parents. Hybrids selected in HAT medium alone or HAT plus OLI retained primarily mouse mitochondrial DNA while those selected in HAT plus CAP, or HAT plus CAP plus OLI retained both species of mitochondrial DNA. There was no evidence for mitochondrial DNA recombination, despite the continued growth of these hybrids in CAP plus OLI. Hybrids that were removed from dual antibiotic selection for over three months retained both species of mitochondrial DNA in approximately equal amounts with no detectable loss or rearrangement.

Propagation of two species of mitochondrial DNA in chinese hamster-mouse somatic cell hybrids

Mouse-hamster hybrid cells were analyzed for the species of mitochondrial DNA (mtDNA) retained using Southern blotting and hybridization with highly labeled mitochondrial DNA probes. Initial analyses were performed as soon as there were 10(7) cells, which took between five and eight weeks from the time the fusion was performed (approximately 23 cell doublings). The majority of clones tested had detectable levels of both mouse and hamster mtDNA at first testing.

Uniparental propagation of mitochondrial DNA in mouse-human cell hybrids

The retention of the two parental mitochondrial DNAs has been investigated in a large number of mouse-human cell hybrids segregating either mouse or human chromosomes, by using a highly sensitive and specific method for detection of the DNA; the results have been correlated with the karyotype and isozyme marker pattern in the same hybrid lines. In all the hybrids examined, a consistent pattern was observed for the type of mitochondrial DNA retained: the mitochondrial DNA of the parent whose chromosomes were segregated from the nucleus was undetectable or present in marginal amounts. This was true also of hybrids containing a complete set of the segregating chromosomes in the total or a large fraction of the cell population.

Ribonucleic acid synthesis in normal and immune macrophages after antigenic stimulus

Macrophage ribonucleic acid (RNA) synthesis is an important metabolic process intimately related to the function of these cells. Mouse peritoneal macrophage RNA was extracted with phenol in the presence of bentonite and electrophoresed on composite agarose-polyacrylamide gels. The pulse-chase technique was used to follow the precursor relationships in macrophage ribosomal RNA (rRNA) maturation. The rRNA species at 18S and 28S appeared at 15 and 45 min, respectively, after RNA synthesis was halted. Their appearance corresponded closely to decreases in the rRNA precursors at 45S, 36S, and 34S. Studies of RNA methylation aided in confirming the identity of these ribosomal species. Unmethylated RNA species appeared as messenger RNA between 5S and 15S, and at about 55S probably represented heterodisperse nuclear RNA. When normal macrophages were incubated with heat-killed Salmonella enteritidis, an acceleration in the maturation of RNA was observed. The accelerated maturation was indicated by the earlier appearance of 28S rRNA and the more rapid development of an equilibrium state, where further labeling did not change the RNA profile. In macrophage RNA from mice immunized with S. enteritidis, rRNA species appeared rapidly but did not accumulate to the same extent as observed for normal macrophages. Precursor rRNA and other RNA species developed as usual, suggesting specific degradation of mature rRNA. Such rRNA wastage could indicate a mechanism controlling ribosome assembly in the non-proliferating activated macrophage. The pattern of RNA synthesis in immune macrophages was essentially unchanged by the presence of heat-killed S. enteritidis in vitro.

Ribosomal proteins of hamster, mouse and hybrid cells

We hhave been analyzing what could be considered to be structural ribosomal proteins, that is, those that remain with the ribosome when it has been subjected to centrifugation through 1.75 M sucrose, treatment with puromycin and KCl, and centrifugation through 0.5 M KCl and sucrose. By two-dimensional gel electrophoresis, a mouse-specific protein and a Syrian hamster-specific protein are detected, using liver or cultured cell lines. With liquid scintillation counting after two-dimensional gel electrophoresis it is possible to estimate the proportion of species-specific ribosomal protein in a mouse-hamster somatic cell hybrid.

Regulation of species-specific ribosomal RNA in a somatic hybrid cell

When 13B hamster-mouse hybrid cells are harvested either right after 4 h of incubation with [me-3H]methionine or following 26 h of "chase" with excess non-radioactive methionine, in both cases about half of the labeled cytoplasmic rRNA is of hamster type. It had been previously shown in this laboratory (Eliceiri, G.L. (1973) Biochim. Biophys. Acta 312, 737-741) that when [3H]uridine was the radioactive precursor about 80% of the labeled cytoplasmic rRNA was of hamster type after a short incubation, and about half after a long incubation. It is postulated that a temporary difference in the specific acitivity of [3H]UTP in possibly segregated mouse and hamster types of nucleoli might account for these results. The master/mouse ratio of cytoplasmic rRNA in hybrid 13B is similar in free and in membrane-bound ribosomes, and in ribosomes of sparse (rapidly growing) cell populations and of confluent (slowly growing) cells.