Obtaining mice that carry human mitochondrial DNA transmitted to the progeny

To study human diseases associated with mutations in mitochondrial DNA one needs an animal model in which the distribution of abnormal mtDNA and its impact on the phenotype might be followed. We isolated human mitochondria from HepG2 cell culture and microinjected them into murine zygotes, upon which those were transplanted to the pseudopregnant mice. PCR with species-specific primers allowed detecting human mtDNA in the tissues of 7-13-day embryos. No serious alterations in the development of transmitochondrial embryos were noticed. Among various organs/tissues of the 13-day embryos, human mtDNA was detected only in the heart, skeletal muscles, and stomach, which is in line with its uneven distribution among the blastomeres of an early mouse embryo that we described previously. In four recipient females, the microinjected zygotes were allowed to develop to term, the four neonate males of their joint litter were sacrificed, and in three of them human mtDNA was detected in the heart, skeletal muscles, stomach, brain, testes, and bladder. Six females of that joint litter were grown and mated to intact males. In the progeny (F1) of one of the females two mice were carrying human mtDNA in the heart, skeletal muscles, stomach, brain, lungs, uterus, ovaries, and kidneys. The study confirms the possibility to obtain transmitochondrial mice carrying human mtDNA that is transmitted to the animals of the next generation. Our results also indicate that among the organs to which human mtDNA is distributed some are more likely to receive it than others.     

Bovine satellite DNA induces heterochromatinization of host chromosomal DNA in cells of trassatellite mouse embryonal carcinoma

Embryonal teratocarcinoma F9 cells were transfected with a fragment (3.8 kb) of bovine satellite DNA IV (Sat), which is not homologous to mouse satellite DNA. FISH analysis revealed various chromosomal integration sites of integrated Sat in different transsatellite clones. After several passages, transsatellite had a tendency to spread along chromosome bearing Sat in one of the studied lines. The integrated transsatellites were enriched with prolonged single-strand DNA regions (SSR) revealed by FISH without previous chromosomal denaturation, and were unmethylated. The observed SSR are presumably supposed to represent intermediates of transsatellite DNA instability via unequal sister chromatid exchanges. DAPI staining demonstrated that the integrated Sat induced the formation of prominent ectopic neoheterochromatin blocks in regions adjacent to integrated Sat. These blocks were located exclusively between integrated Sat and centromeric heterochromatin. Thus, mouse repetitive centromeric DNA (AT-rich, DAPI-positive) "spreads" along the chromosome in response to integration of the bovine satellite GC-rich DNA. The results obtained are discussed in the context of possible position effect variegation mechanisms operating in undifferentiated cells.     

Single-strand DNA breaks in brain cells of different rat strains under normal condition and during exposure to stress

This study was aimed to characterize pattern of occurrence of spontaneous single-strand breaks in situ in glial and neuronal nuclei of the cortex, middle brain and hyppocapmi (CA3 field) of rats selected for a threshold of nervous system excitability, and to study the influence of stress of various modality on such breaks. The results obtained evidence that: 1) intact animals possess a subpopulation of glial and neuronal cells revealed following gap filling in situ in opposite to other types of terminally differentiated non-proliferating cells; 2) the size of such a subpopulation differs depending on the lines of examined rats, parts of brain, and the type of stress.     

Increased Brain Levels of Platelet-Activating Factor in a Murine Acquired Immune Deficiency Syndrome Are NMDA Receptor-Mediated

Abstract: Mice infected with the LP-BM5 murine leukemia virus (MuLV) develop an immunodeficiency syndrome (murine AIDS) and an encephalopathy characterized by impaired spatial learning and memory. Because platelet-activating factor (PAF) has been implicated in the pathogenesis of HIV-associated dementia complex, brain PAF levels were measured in LP-BM5 MuLV-infected mice. PAF levels in cerebral cortex and hippocampus were significantly increased at 6 and 12 weeks after LP-BM5 MuLV inoculation, whereas significant increases in striatal and cerebellar PAF levels were observed only at 12 weeks after inoculation. Administration of the NMDA antagonist MK-801 significantly reduced the increased PAF levels in the cerebral cortex and hippocampus of LP-BM5 MuLV-infected mice. These results indicate that the LP-BM5 MuLV-induced increases in brain PAF levels are the result of NMDA receptor activation and are consistent with the hypothesis that elevated CNS PAF levels contribute to the behavioral deficits observed in LP-BM5 MuLV-infected mice.     

Instability of repetitive units of foreign centromeric satellite DNA in transgenic mice and transfected cells

Cytologically detectable instability of centromeric satellite DNA may cause hereditary disorders in human. To study the mechanisms of such instability, two transgenic mouse lines and 11 clones of transfected F9 mouse embryonic teratocarcinoma cells were obtained with the 3.8-kb repetitive unit (Sat) of Bos taurus satellite DNA IV. Intergeneration and somatic instability of exogenous satellite DNA (satDNA) was observed in transgenic mice and transfected cells as a change in nucleotide sequence of an internal Sat region approximately 1000 bp in size. Since Sat was in the hemizygous state in both cases by the experimental protocol, the instability was attributed to intra-allelic processes. Intergeneration instability probably took place in the premeiotic period of gametogenesis or in early embryo development and led to prenatal death of transgenic embryos after at least one generation. No direct or inverse correlation was observed between methylation and instability of Sat. The results testify that submicroscopic changes in highly repetitive noncoding DNA sequences may already affect the genome function in higher eukaryotes.     

Distribution of foreign mitochondrial DNA during the first splitting of transmitochondrial mouse embryos

The distribution of human mitochondrial DNA (mtDNA) among single murine blastomeres was analyzed during the splitting of embryos injected with a suspension of human mitochondria at the one- or two-cell stage. Human mtDNA was detected by PCR with species-specific primers. The total amount of the- and four-cell murine embryos analyzed in the study was 315. In all embryos examined together with murine mtDNA copies of human mitochondrial genome were revealed indicating the phenomenon of an artificially modeled heteroplasmy. Foreign mtDNA was not ubiquitous in blastomeres of transmitochondrial embryos. Mathematical treatment of the results showed that, in the period between the injection of human mitochondria and the subsequent embryo cleavage, an uneven distribution of human mtDNA occurred in the cytoplasm. These results also indicate the presence of more than two to three segregation units of mtDNA in the entire pool of mitochondria (about 500) introduced into an embryo by microinjection.