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Biomedical subjects

R Jaenisch

Publications and source records attributed to R Jaenisch.

At least 271 records · Page 15Linked to original sources
PubMed1976

Infection of developing mouse embryos with murine leukemia virus: tissue specificity and genetic transmission of the virus.

The tissue specificity of Moloney leukemia virus (M-MuLV) was studied by infecting mice at two different stages of development. Either newborn mice which can be considered as essentially fully differentiated animals were infected with M-MuLV or preimplantation mouse embryos were infected in vitro at the 4-8 cell stage, a stage of development before any differentiation has taken place. After surgical transfer to the uteri of pseudopregnant surrogate mothers, the latter developed to term and adult mice. In both cases, animals were obtained that had developed an M-MuLV induced leukemia. Molecular hybridization tests for the presence of M-MuLV-specific sequences were conducted on DNA extracted from different tissues of leukemic animals to determine which tissues were successfully infected by the virus. Mice which were infected as newborns carried M-MuLV-specific DNA sequences in "target tissues" only, i. e., thymus, spleen, lymph nodes or in organs infiltrated by tumor cells, whereas "non-target tissues" did not carry virus-specific sequences. In contrast, when leukemic animals derived from M-MuLV-infected preimplantation embryos were analyzed, virus-specific sequences were detected in target tissues as well as in non-target tissues, such as liver, kidney, brain, testes and the germ line. To study the expression of the viral DNA integrated in target and non-target organs, RNA was extracted from different tissues of an animal infected at the preimplantation stage. Fifty to 100 times more M-MuLV-specific RNA was detected in tumor tissues than was found in non-target organs. Since all organs contained the same amount of virus-specific DNA, these results indicate that the integrated virus genome can be differentially expressed in different tissues. The organ-tropism of RNA tumor viruses is discussed in view of these findings. Mice that were infected at the preimplantation stage were found to have M-MuLV integrated into their germ line. Virus transmission from the father to the offspring occurred according to simple Mendelian expectations. Molecular hybridization tests revealed that in the animals studied, the virus was integrated into the germ line at only one out of two or three possible integration sites. During the development of leukemia amplification of this virus copy was observed in the target tissues only, but not in the non-target tissues.

Animals↗
PubMed1976

Germ line integration and Mendelian transmission of the exogenous Moloney leukemia virus.

Mice were infected with the exogenous Moloney leukemia virus (M-MuLV) at two different stages of development. Either newborn mice (which can be considered as essentially fully differentiated animals) or preimplantation mouse embryos (at the 4-8 cell stage) were infected with M-MuLV. In both cases, animals that had developed an M-MuLV-induced leukemia were obtained. Two lines of evidence indicate that infection of preimplantation embryos, in contrast to infection of newborns, can lead to integration of the virus into the germ line. 1. Viremic males of the first backcross generation (N-1 generation) transmitted the virus to 50% of their offspring (N-2 generation) when mated with uninfected females. Likewise, a 50% transmission was observed from viremic N-2 and N-3 males to the next generations. 2. Molecular hybridization experiments revealed that viremic N-1 and N-2 animals carried one copy of M-MuLV per diploid mouse genome equivalent in all "non-target" organs tested. Together, both experiments indicate that the exogenous M-MuLV can be converted to an endogenous virus after infection of preimplantation embryos. The available evidence suggests that M-MuLV integrated into the germ line at one out of two possible integration sites. Thus, viremic backcross animals are heterozygous for a single Mendelian locus carrying the M-MuLV gene. During leukemogenesis an amplification of the M-MuLV from one copy to a maximum of four copies per diploid mouse genome equivalent takes place in the tumor tissues.

Animals↗
PubMed1976

Increase of AKR-specific sequences in tumor tissues of leukemic AKR mice.

AKR mice produce, from shortly after birth, high titers of their endogenous Gross type murine leukemia virus, and develop a thymus-derived leukemia at 7-9 months of age. We show that this oncogenesis is accompanied by an increase in the number of AKR-specific DNA sequences in the tumor tissues, whereas the "non-target" organs are not affected. Sequence increase was determined by kinetic analysis of DNA reassociation using an AKR-murine leukemia virus (MuLV)-specific cDNA and also by hybridization with excess AKR cDNA. The AKR cDNA was selected to recognize AKR sequences without significant crossreaction with DNA sequences of other endogenous viruses. The results show that during the development of the leukemia, the number of AKR-MuLV-specific genes increases in tumor tissues by a factor of 1 1/2 to 2.

AKR murine leukemia virus↗
PubMed1975

Infection of preimplantation mouse embryos and of newborn mice with leukemia virus: tissue distribution of viral DNA and RNA and leukemogenesis in the adult animal.

Explanted mouse embryos derived from low leukemia incidence strains were infected with Moloney murine leukemia virus (M-MuLV) at the 4-8 cell stage of development. After cultivation in vitro to the blastocyst stage, the embryos were surgically transferred to the uteri of pseudo-pregnant surrogate mothers. Of 15 animals born, one developed a leukemia at 8 weeks of age. When autopsied, this leukemia was found to be of the lymphatic type, as is typical for the M-MuLV-induced disease. In addition, infectious M-MuLV virus was isolated from the serum. Molecular hybridization tests for the presence of M-MuLV-specific sequences were conducted on DNA and RNA extracted from eight different organs. The DNA-DNA reannealing experiments revealed the presence of two classes of M-MuLV-specific sequences in equal concentrations in all tissues tested. The less abundant class of M-MuLV-specific sequences was not detected in tissues from uninfected animals or in non-target tissues of leukemic animals infected at birth. The results are consistent with the working hypothesis that the virus was integrated in all cells of the animal, possibly including the germ line. Fifty to 100 times more M-MuLV-specific RNA was detected in tumor tissues than was found in non-target organs such as liver, brain, and testes. Since all organs contained the same amount of virus-specific DNA, these results indicate that the M-MuLV-specific DNA can be differentially expressed in different tissues.

Animals↗
PubMed1975

Infection of mouse blastocysts with SV40 DNA: normal development of the infected embryos and persistence of SV40-specific DNA sequences in the adult animals.

In SV40-transformed culture cells, viral-specific sequences have been found to be covalently linked to host sequences (Sambrook et al. 1968). The most appealing interpretation to explain the presence of SV40-specific sequences in adult mice following infection at the preimplantation stage would be to assume that the viral DNA was integrated at this early stage of development into the host genome and was thus conserved during further development. However, our results do not exclude an extrachromosomal existence of the SV40 genome, for example, as an independently replicating plasmid or as a lytic infection in a few permissive cells. So far our attempts to demonstrate autonomous SV40 DNA replication in early mouse embryos have been unsuccessful. We plan to investigate whether the SV40-specific information can be genetically transmitted from the infected mice to their offspring; chromosomal integration would be proven if transmission of SV40 DNA occurred in accordance with simple Mendelian expectations. The injection of mouse blastocysts with purified SV40 DNA did not detectably interfere with normal development of the embryos to healthy adult mice, which were still tumor-free at one year of age. This was not due to the trivial possibility that the viral DNA did not successfully infect and was eliminated from the injected embryos, as virus-specific DNA sequences were detected in 40% of the infected year-old animals, or in about 25% of DNA preparations extracted from some of their tissues (Table 1). It is nevertheless possible that the animals may not have been old enough to exhibit tumorigenesis of SV40 origin; to test this possibility, the experiment will have to be repeated for longer survival periods. The absence of any obvious signs of expression of viral genetic functions, i.e., tumor formation, up to one year of age of the host is reminiscent of the "cryptic transformants" described earlier (Smith et al. 1972) which harbor SV40 information but behave essentially like normal untransformed cells. Whether transcription or translation of the virus gene can occur in infected mice is presently an open question. Testing for expression of an integrated viral genome in diverse differentiated tissues may provide a useful model system to study the regulation of differentiation. These matters are currently being investigated.

Animals↗
PubMed1974

Simian virus 40 DNA sequences in DNA of healthy adult mice derived from preimplantation blastocysts injected with viral DNA.

Explanted mouse blastocysts were microinjected in the blastocoel cavity with simian virus 40 (SV40) viral DNA. After surgical transfer to the uteri of pseudopregnant surrogate mothers, approximately 40% of the blastocysts developed to term and became healthy adults without apparent tumors at 1 year of age. Molecular hybridization tests for the presence of SV40-specific DNA sequences were conducted on DNA extracted from various organs of these animals. Between 0.5 and 13 SV40 genome equivalents per diploid mouse DNA value were found in some organs of approximately 40% of the adult survivors; this represents a substantial augmentation of the amount administered per embryo. The results are consistent with the working hypothesis that the SV40 DNA may have been integrated into the host genome; alternatively, the viral DNA may have replicated as an extrachromosomal entity or by lytic infection in a few permissive cells. Persistence of the viral DNA from preimplantation stages to adult life may thus provide a new tool for experimental investigation of vertical transmission and expression of tumor viruses.

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