K. F. Meyer. In memoriam.
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Biomedical subjects
Publications and source records attributed to W P Rowe.
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Strain BALB/c mice were injected intraperitoneally with 0.5 milliliter of pristane, and 39 to 56 days later they were infected with Abelson murine leukemia virus, which is a lymphosarcomagenic variant of Moloney virus. Fifty-eight percent of the mice developed lymphosarcoma, and 28 percent developed immunoglobulin-producing plasmacytomas within 20 to 93 days (77 to 149 days after the pristane injection). Two of 57 control mice developed plasmacytomas at days 138 and 166 after a single injection of pristane; no plasmacytomas were found in mice treated with virus alone.
The Fv-l locus of the mouse, a major determinant of the biology of murine leukemia virus, is very closely linked to Gpd-1 on chromosome 4 (linkage group VIII).
Genes specifying or controlling the expression of G(IX) (cell surface), GCSA (cell surface), and gs (internal viral) antigens are located in chromosome 4 (linkage group [LG] VIII) of the AKR mouse. All three antigens may exhibit mendelian inheritance, mice being antigen positive or antigen negative, but each may also appear in leukemic cells of mice whose inherited genotype was antigen negative. The G(IX)-determining gene in LG VIII of AKR mice apparently is equivalent to Gv-1, which determines expression of the same antigen in 129 strain mice, but which in the latter strain is located in LG IX. As the estimated distance of Gv-1 from H-2 in 129 mice is considerable (37 units) further tests are now indicated to assess the possibility of pseudolinkage in this case. The Fv-1 locus, also located in LG VIII, influences the mouse's titer of MuLV, and might thereby be thought to regulate the G(IX) and gs phenotypes of AKR backcross segregants. But the data indicate a discrete LG VIII locus for G(IX), since expression of this antigen is mendelian and independent of infectious virus titer. Since the G(IX) and GCSA phenotypes of AKR backcross segregants were invariably concordant, these two antigens must be specified or controlled by closely linked genes, and the latter also is presumably independent of virus titer. The question as to what extent expression of gs antigen in the segregants is secondary to virus production is undecided.
The Fv-1 gene, which regulates sensitivity of mouse cells to infection by naturally occurring host-range types of murine leukemia virus, was shown to be located on linkage group VIII (chromosome 4), 39 map units from b.
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Two of the five nondefective adenovirus 2 (Ad2)-simian virus 40 (SV40) hybrids induce SV40 transplantation resistance in immunized hamsters. These two hybrids, Ad2(+)ND(2) and Ad2(+)ND(4), contain 32 and 43% of the SV40 genome, respectively. The pattern of induction of SV40 transplantation antigen (TSTA) by the various hybrids differentiates TSTA from both SV40 U and T antigens. Since the SV40 RNA induced by both these hybrids is early SV40 RNA, these findings confirm that TSTA is an early SV40 function. By combining available data on SV40 antigen induction by these hybrids with electron microscopy heteroduplex mapping studies, the DNA segment responsible for the induction of SV40 TSTA can be inferred to lie in the region between 0.17 and 0.43 SV40 units from the site on the SV40 chromosome cleaved by E. coli R(1) restriction endonuclease.
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The chromosomal location of one of the two murine leukemia virus-inducing loci of AKR mice has been determined. The locus, which appears to be the integrated genome of the virus, is designated Akv-1, and is on linkage group 1, 12 map units from Gpi-1, with gene order c-Gpi-1-Akv-1. This identification of a closely linked gene whose phenotype is independent of virus expression should facilitate analysis of the biologic importance of the Akv-1 locus.
AKR mice, which regularly contain infectious murine leukemia virus, were mated with four Fv-1(n) strains of mice which show little or no expression of virus. F(1), F(2), and first and second backcross generation hybrids were tested for virus in tail tissue at 2 and 6 wk of age. The segregation data indicate that the AKR mouse contains two unlinked, autosomal, chromosomal loci, either of which suffices to induce detectable levels of infectious virus in Fv-1(n) progeny by 6 wk of age. One of the loci (tentatively referred to as V(1)) is on linkage group I, 25-30 map units from the locus for albino; the gene order tentatively appears to be N(1)-c-Hbb.
The transmission of murine leukemia virus (MLV) to hybrids between AKR and Fv-1(b) mice was studied in order to evaluate the effect of the Fv-1 gene on endogenous MLV infection and to attempt to determine if the genetic loci contributed by AKR carry viral genetic determinants. Fv-1 was shown to have a marked suppressive effect on time of appearance of detectable infectious virus and on the titers attained in vivo, but did not affect the ability of the cells to produce virus in vitro after induction with 5-iododeoxyuridine. The host range type of the virus detected in the hybrid mice was almost always of the type carried by AKR, although the low-virus Fv-1(b) parents carry the genome of a different host range type. This finding provides strong, but not conclusive, evidence that the virus-inducing loci of AKR contain MLV genetic determinants.
Quantitative studies were made of the organ distribution of murine leukemia virus in AKR mice of various ages. Infectious virus first appeared shortly before or after birth and was continuously present in all mice thereafter. Highest infectivity titers were found in uterus and bone, with spleen slightly lower. Virus titers in normal thymus were relatively low, but increased significantly with the development of thymic lymphoma. The level of viremia decreased after the 1st month of life, but increased sharply in lymphomatous mice.
Genetic information of murine leukemia viruses is known to be present in essentially all mice. Delineation of the biological effects of the expression of this genetic information is complicated by the difficulty in determining whether the presence of a viral antigen in a tissue is the result of gene activation that occurs independently in a large number of cells, proliferation of antigen-positive cells, or of spread of infectious virus from a few cells. This problem is further complicated by the difficulty in determining whether activation of virus genetic material is the cause or result of a biological phenomenon, such as malignancy. Further understanding of the activation of virus genes in normal cells is of great importance in answering these questions. In vitro techniques were used for the study of induction of virus. Virus-negative cell lines were established from embryos of AKR mice, which in vivo produce high titers of infectious murine leukemia virus. It was found that 5-iododeoxyuridine and 5-bromodeoxyuridine were potent inducers of virus synthesis in all clones and subclones of the AKR cells tested. In addition to establishing that the complete viral genome is a heritable component of all cells of the AKR mouse, these studies of virus activation provide novel approaches to a number of important problems in the biology of leukemia viruses.
Cells of embryos of the high leukemic mouse strain AKR can be grown in culture as virus-negative cell lines. However, these lines and clonal sublines uniformly have the capacity to initiate synthesis of murine leukemia virus. Exposure of the cells to 5-iododeoxyuridine or 5-bromodeoxyuridine induced synthesis of virus in as high as 0.1 to 0.5 percent of the cells; many of the cells were producing virus as soon as 3 days after initiation of treatment. Induction of virus by these drugs is several orders of magnitude greater than that obtained with any other treatment tested. These studies indicate that the full genome of murine leukemia virus is present in an unexpressed form in all AKR cells and provide a potentially powerful technique for activating leukemia virus genomes in other cell systems.
Previous studies have indicated that all naturally occurring murine leukemia viruses propagate significantly more efficiently on embryo cells of either NIH Swiss or BALB/c mice. Studies of the plaquing efficiency of representative viruses on embryo cells of various inbred and hybrid mice indicate that the pattern of sensitivity of the cells is genetically determined. All of 23 strains tested were found to resemble either NIH Swiss (N-type) or BALB/c (B-type) with respect to plaquing efficiency of these viruses. Virus growth on embryo cells derived from (N-type x B-type)F(1) hybrids indicated dominance of resistance to both types of viruses. Backcross hybrid studies indicated that a single locus is the primary determinant of the host-range patterns observed. This locus has no effect on growth of certain laboratory-passaged leukemia viruses which propagate equally well on embryo cells of all mouse strains, F(1), and backcross hybrids. Though other genetic and nongenetic factors influence viral growth or expression in vitro and in vivo, the genetic locus described appears of major significance in the biology of murine leukemia.
The N-B locus affecting tissue culture infectivity with naturally occurring murine leukemia viruses appears to be identical to the Fv-1 locus described for sensitivity to Friend leukemia virus. Results of tissue culture studies were parallel to results of studies in vivo and indicate that the F-S virus is N-tropic and the F-B virus is NB-tropic. Inbred and partially congenic mouse strains sensitive at Fv-1 show N-type sensitivity; strains resistant at Fv-1 show B-type sensitivity. The Fv-2 locus does not appear to exert significant effect in tissue culture. Knowledge of N-B type has been useful in predicting Fv-1 sensitivity.