Virus-specific transcription and translation in organs of BALB/Mo mice: comparative study using quantitative hybridization, in situ hybridization, and immunocytochemistry

10A1-MuLV but not the related amphotropic 4070A MuLV is highly neurovirulent: importance of sequences upstream of the structural Gag coding region

Recombinants of Moloney murine leukemia virus (MoMuLV) with either an amphotropic (MoAmphoV) or 10A1-tropic host range (Mo10A1V) induce a spongiform neurodegenerative disease in susceptible mice. To test whether MoMuLV -derived sequences are required for induction of neuropathology, mice were inoculated with either the original 10A1 or the amphotropic (4070A) MuLV isolate. Strikingly, wild-type 10A1 was more neurovirulent than Mo10A1V, inducing severe neurological clinical symptoms with a median latency of 99 days in 100% of infected mice. In contrast, no motor disturbances were detected in any of the 4070A-infected mice, although limited central nervous system lesions were observed. A viral determinant conferring high neurovirulence to 10A1 was mapped to a region encompassing the first 676 bases of the viral genome, including the U5 LTR and encoding the amino-terminus of glycosylated Gag (glycoGag). In contrast to studies with the highly neurovirulent CasFr(KP) virus, an inverse correlation between surface expression levels of glycoGag and neurovirulence was not observed; however, this does not rule out a common underlying mechanism regulating virus pathogenicity.

Entry of amphotropic and 10A1 pseudotyped murine retroviruses is restricted in hematopoietic stem cell lines

Although transduction with amphotropic murine leukemia virus (MLV) vectors has been optimized successfully for hematopoietic differentiated progenitors, gene transfer to early hematopoietic cells (stem cells) is still highly restricted. A similar restriction to gene transfer was observed in the mouse stem cell line FDC-Pmix compared with transfer in the more mature myeloid precursor cell line FDC-P1 and the human erythroleukemia cell line K562. Gene transfer was not improved when the vector was pseudotyped with gp70SU of the 10A1 strain of MLV, which uses the receptor of the gibbon ape leukemia virus (Pit1), in addition to the amphotropic receptor (Pit2). Although 10A1 and amphotropic gp70SU bound to FDC-P1, K562, and fibroblasts, no binding to FDC-Pmix cells was detected. This indicates that FDC-Pmix cells lack functional Pit2 and Pit1 receptors. Pseudotyping with the vesicular stomatitis virus G protein improved transduction efficiency in FDC-Pmix stem cells by 2 orders of magnitude, to fibroblast levels, confirming a block to retroviral infection at the receptor level.

Thymic targets for Abelson murine leukemia virus are early gamma/delta T lymphocytes

Molecular analysis has shown that the majority of Abelson murine leukemia virus (Ab-MuLV)-induced primary thymomas represent transformed gamma/delta thymocytes. Many of these thymomas are of monoclonal origin as judged by provirus integration pattern and contain rearranged genes encoding T-cell receptor (TCR) gamma and delta chains but germ-line immunoglobulin heavy-chain genes. Some of the monoclonal tumors contain multiple rearranged alleles encoding TCR gamma, delta, and beta chains. Further, one Ab-MuLV thymoma cell line contained germ-line-configuration TCR gamma- and delta-chain genes, which became rearranged after in vitro propagation. Clones of this cell line were observed to rearrange these genes after intrathymic passage. Also, some subclones of this cell line underwent rearrangement of their immunoglobulin heavy-chain genes in culture. These observations suggest that the thymic targets for Ab-MuLV transformation are early gamma/delta thymocytes, some of which continue to rearrange their TCR gamma- and delta-chain genes.

Experimentally introduced defective endogenous proviruses are highly expressed in chickens

We have previously described the experimental introduction of recombinant subgroup A avian leukosis viruses (ALV) with Rous-associated virus 0 long terminal repeats into the germ line of line 0 chickens and the generation of 23 transgenic lines. Two of these transgenic lines, alv6 and alv11, do not produce infectious virus. Both of these lines contain defective proviruses but do express the gag and/or env protein. We have measured viral RNA expression in tissues derived from alv6, alv11, and the parental line 0. Total RNA was prepared from 9-day embryo, 16-day embryo, 1-day chicken, and 28-day chicken tissues. Viral RNA was detected by Northern RNA transfer analysis. The results indicate that both alv6 and alv11 chickens express viral RNA in all tissues tested regardless of the stage of development. No viral transcripts were detected in any line 0 (C/E; ev-negative) tissue. The levels of biologically active env glycoprotein correlates with the env RNA levels in both lines. In an in vivo interference assay, alv6, alv11, and line 0 chickens were infected with Rous-associated virus 1 and monitored for viremia, antibody against Rous-associated virus 1, and ALV-induced pathogenesis from 4 to 21 weeks. None of the 61 alv6 chickens contained detectable virus or produced antibody against subgroup A ALV. Virus and/or antibody against subgroup A ALV was detected in 34 of the 43 alv11 chickens, whereas 51 of 52 line 0 birds were viremic and/or produced antibody. ALV-induced pathogenesis was observed predominantly in line 0 chickens (10 of 59), whereas very little ALV-induced pathogenesis was seen in either alv6 (1 of 62) or alv11 (1 of 44) chickens. Presumably the mechanism for the increased resistance of alv6 and alv11 chickens was subgroup-specific receptor interference. These results clearly demonstrate that experimentally introduced endogenous proviruses can be expressed at high levels in the avian system.

Histo-blotting: hybridization in situ detection of specific RNAs on tissue sections transferred on nitrocellulose

A simple and rapid variant of in situ hybridization on tissue sections (histo-blotting) usable for detection of specific RNA distribution among tissues is proposed. Tissue sections prepared with a cryostatic microtome are placed on nitrocellulose and these "histo-blots" are hybridized with labelled DNA or RNA probes under conditions of Northern-blot hybridization without any particular pretreatment. Tissue specificity of the RNA distribution may be determined by comparison of autoradiograms with the histological structure of the stained section. Histological staining and light microscopy may be carried out after hybridization of histo-blots. Hybridization in situ may be easily combined with immunostaining under conditions of immunoblotting. Application of the proposed method is shown for alfa-fetoprotein (AFP) and endogenous provirus (ev-3) RNA detection in rat and chicken embryos, respectively. Histo-blotting results correlate with the distribution of given RNAs among tissues determined by independent methods. Sensitivity, specificity and resolution of histo-blotting have been evaluated and discussed.

Retrovirus-induced insertional mutation in Mov13 mice affects collagen I expression in a tissue-specific manner

In the Mov13 mouse mutant, transcription of the alpha 1 (1) collagen gene is blocked by a retroviral insert in the first intron. We now report that teeth derived from homozygous embryos produce a dentin layer containing normal amounts of collagen 1. In situ hybridization and RNAase protection experiments indicate that the mutant allele is efficiently transcribed in odontoblasts, in contrast to other cell types. Correct splicing of the primary transcript containing the viral sequence results in a functional alpha 1 (1) collagen mRNA. The absence of a mutagenic effect in odontoblasts, as opposed to fibroblasts, suggests that the retroviral insert interferes with tissue-specific transcriptional control of the alpha 1 (1) collagen gene, most likely by inactivating cell-type-specific cis-acting regulatory elements.

Tissue specificity of retrovirus expression in inoculated avian embryos revealed by in situ hybridization to whole-body section

To examine the mechanism of viral tropism in vivo, we injected RAV(1) avian retrovirus into 1-day-old chicken embryos. After 8 days, the majority of the embryos became infected. In situ hybridization to whole embryo sections revealed high levels of intracellular viral RNA, apparently restricted to skeletal muscle cells. The most likely interpretation is that expression of this virus is regulated at the transcriptional level by one or more tissue-specific endogenous factors.

Comparison and optimization of in situ hybridization procedures yielding rapid, sensitive mRNA detections

This paper describes methods that are commonly used for performing mRNA in situ hybridizations. Each stage of the procedure has been analyzed to identify the parameters that most significantly affect the final cell morphology and sensitivity of the system. We have identified key elements of the procedure as the fixation employed, the type of polynucleotide probe and label chosen, and the detection system used. By optimizing these critical components, we have developed a procedure for performing mRNA in situ hybridizations that takes 2-4 hours and has a sensitivity of 1-10 molecules of mRNA per cell. This system has been used to detect levels of oncogene expression in normal bone marrow and peripheral blood. It is possible to detect the expression of three oncogenes (c-myc, c-sis, and c-abl) simultaneously in a small population of cells from the peripheral blood of leukemic patients.

Retroviral gene transfer into primary hepatocytes: implications for genetic therapy of liver-specific functions

The liver is an important target for potential gene therapy because of the critical role it plays in intermediary metabolism and synthesis of serum proteins. We report the use of retroviral vectors for transfer of recombinant genes into primary mouse hepatocytes. Hepatocytes were grown in a defined serum-free medium and expressed liver-specific functions for up to 14 days. Hepatocytes were transformed to Genticin (G418) resistance by infection with recombinant retroviruses carrying the Tn5 neomycin-resistance gene. The G418-resistant cells exhibited characteristic hepatocyte morphology and continued to express liver-specific gene function. A retrovirus that expresses neomycin resistance driven by a herpes simplex thymidine kinase promoter produced the most efficient transformation compared with viruses using the retroviral long terminal repeat promoter or the simian virus 40 early-region promoter. These experiments indicate that primary hepatocytes can be successfully cultured and transformed with recombinant genes using retroviral vectors. These results provide a model for future somatic gene replacement therapy in which functional genes can be introduced into hepatocytes by viral-mediated gene transfer.

Lymphoid and other tissue-specific phenotypes of polyomavirus enhancer recombinants: positive and negative combinational effects on enhancer specificity and activity

Heterologous enhancer recombinants and deletions of the polyomavirus (Py) noncoding region were constructed and analyzed for tissue specificity of DNA replication and transcription in a number of lymphoid and other cell lines. The simian virus 40 72-base-pair repeat, mouse immunoglobulin heavy-chain enhancer, and Moloney murine leukemia virus enhancer were inserted into the PvuII-D locus (nucleotides 5128 through 5265) of Py. The ability of these recombinants and the parental PvuII-D deletion mutant to replicate in permissive 3T6 cells and MOP-6 cells as well as in nonpermissive mouse B lymphoid, T lymphoid, mastocyte, and embryonal carcinoma cells was determined. Wild-type Py DNA was not permissive for replication in most lymphoid cell lines, except one hybridoma line. Simply deleting the Py PvuII-D region, however, gave Py an expanded host range, allowing high-level replication in some T lymphoid and mastocytoma cell lines, indicating that this element can be a tissue-specific negative as well as positive element. Substitution of the murine leukemia virus enhancer for Py PvuII-D yielded a Py genome which retained the ability to replicate in 3T6 cells but also replicated well in B lymphoid cells. Substitution with the immunoglobulin heavy-chain enhancer allowed replication in B lymphoid cells but interfered with replication in 3T6 cells and mastocytomas. Surprisingly, substitution with the simian virus 40 72-base-pair enhancer repeat gave a recombinant which would not replicate in any cell line tried, including MOP-6 cells, even though other recombinants with this enhancer would replicate. Thus, we observed both cooperation and interference in these combinations between enhancer components and the Py genome and that these combined activities were cell specific. These results are presented as evidence that there may be a positional dependence, or syntax, for the recognition of genetic elements controlling Py tissue specificity.

Detection of viral-specific nucleic acid and intracellular virions in ventral horn neurons of lactate dehydrogenase-elevating virus infected C58 mice

C58 mice which have been immunosuppressed by treatment with cyclophosphamide (200 mg/kg) one day prior to infection with the C strain of lactate dehydrogenase-elevating virus (LDV-C) develop poliomyelitis. Using in situ hybridisation, we found that some ventral horn neurons in these mice contain cytoplasmic viral-specific nucleic acid. Viral-specific nucleic acid was also found within a few small cells located near inflammatory foci. In addition, mature virus particles were observed by electron microscopy in some ventral horn neurons, indicating that these cells are productively infected in C58 mice. Neither viral nucleic acid nor virions were found in the ventral horn neurons of poliomyelitis-resistant mouse strains or C58 mice that were not immunosuppressed prior to infection. Ventral horn neurons which contained viral nucleic acid or virions within cytoplasmic vesicles generally were normal in appearance and were not located within poliomyelitis inflammatory foci. Our data are consistent with the hypothesis that infected neurons first replicate virus and subsequently are attacked and cleared by inflammatory cells.

Lymphoid and other tissue-specific phenotypes of polyomavirus enhancer recombinants: positive and negative combinational effects on enhancer specificity and activity

Heterologous enhancer recombinants and deletions of the polyomavirus (Py) noncoding region were constructed and analyzed for tissue specificity of DNA replication and transcription in a number of lymphoid and other cell lines. The simian virus 40 72-base-pair repeat, mouse immunoglobulin heavy-chain enhancer, and Moloney murine leukemia virus enhancer were inserted into the PvuII-D locus (nucleotides 5128 through 5265) of Py. The ability of these recombinants and the parental PvuII-D deletion mutant to replicate in permissive 3T6 cells and MOP-6 cells as well as in nonpermissive mouse B lymphoid, T lymphoid, mastocyte, and embryonal carcinoma cells was determined. Wild-type Py DNA was not permissive for replication in most lymphoid cell lines, except one hybridoma line. Simply deleting the Py PvuII-D region, however, gave Py an expanded host range, allowing high-level replication in some T lymphoid and mastocytoma cell lines, indicating that this element can be a tissue-specific negative as well as positive element. Substitution of the murine leukemia virus enhancer for Py PvuII-D yielded a Py genome which retained the ability to replicate in 3T6 cells but also replicated well in B lymphoid cells. Substitution with the immunoglobulin heavy-chain enhancer allowed replication in B lymphoid cells but interfered with replication in 3T6 cells and mastocytomas. Surprisingly, substitution with the simian virus 40 72-base-pair enhancer repeat gave a recombinant which would not replicate in any cell line tried, including MOP-6 cells, even though other recombinants with this enhancer would replicate. Thus, we observed both cooperation and interference in these combinations between enhancer components and the Py genome and that these combined activities were cell specific. These results are presented as evidence that there may be a positional dependence, or syntax, for the recognition of genetic elements controlling Py tissue specificity.

Thymocyte subsets transformed by Abelson murine leukemia virus

The infectious complex of Abelson murine leukemia virus was altered by replacing its usual helper virus, Moloney leukemia virus, with radiation leukemia virus (RadLV). After intrathymic injection of the Abelson-RadLV complex, thymomas arose rapidly, as described previously for injection of the Abelson-Moloney complex. Cell lines were derived from thymomas induced by each Abelson virus complex and were classified according to normal thymus cell phenotypes. Each virus complex induced some cell lines which were like a 0.7% subpopulation of murine thymocytes in that they failed to express the Thy-1 cell-surface antigen. These lines are thus far indistinguishable from some Abelson-derived bone marrow transformants classified as pre-B cells. However, the Abelson-Moloney complex induced some cell lines which expressed low levels of Thy-1 and which shared most markers with immature blast cells of the thymic medulla, whereas the Abelson-RadLV complex induced some lines which were clearly like thymic cortex blast cells. Thus, Abelson virus can induce thymoma cell lines of at least two, and possibly three, distinct phenotypes corresponding to normal thymocyte blast subsets, the determination of which can be influenced by helper virus sequences.

Thymocyte subsets transformed by Abelson murine leukemia virus

The infectious complex of Abelson murine leukemia virus was altered by replacing its usual helper virus, Moloney leukemia virus, with radiation leukemia virus (RadLV). After intrathymic injection of the Abelson-RadLV complex, thymomas arose rapidly, as described previously for injection of the Abelson-Moloney complex. Cell lines were derived from thymomas induced by each Abelson virus complex and were classified according to normal thymus cell phenotypes. Each virus complex induced some cell lines which were like a 0.7% subpopulation of murine thymocytes in that they failed to express the Thy-1 cell-surface antigen. These lines are thus far indistinguishable from some Abelson-derived bone marrow transformants classified as pre-B cells. However, the Abelson-Moloney complex induced some cell lines which expressed low levels of Thy-1 and which shared most markers with immature blast cells of the thymic medulla, whereas the Abelson-RadLV complex induced some lines which were clearly like thymic cortex blast cells. Thus, Abelson virus can induce thymoma cell lines of at least two, and possibly three, distinct phenotypes corresponding to normal thymocyte blast subsets, the determination of which can be influenced by helper virus sequences.