Search PubMed⌕ Search

Biomedical subjects

R Jaenisch

Publications and source records attributed to R Jaenisch.

At least 163 records · Page 9Linked to original sources
PubMed1992

Molecular complementation of a collagen mutation in mammalian cells using yeast artificial chromosomes.

The cloning of large contiguous segments of mammalian DNA in Saccharomyces cerevisiae has become possible with the advent of Yeast Artificial Chromosomes (YACs). We are interested in extending the technique of genetic complementation analysis to the molecular level through the introduction of YACs into mammalian cells and the mammalian germline. We report the successful introduction of homogeneous DNA derived from a 150 kbp YAC spanning the murine Col1a1 locus into murine fibroblasts carrying a mutation at this locus. The YAC DNA was fractionated by pulse field electrophoresis, condensed with polyamines, and introduced into mutant fibroblasts via DNA-lipid micelles. The DNA was integrated as a stable intact unit in 10% of the transfected clones conferring collagen RNA expression to the mutant cells.

Animals↗
PubMed1992

A strategy for rapid production and screening of yeast artificial chromosome libraries.

We describe methods for rapid production and screening of yeast artificial chromosome (YAC) libraries. Utilizing complete restriction digests of mouse genomic DNA for ligations in agarose, a 32,000-clone library was produced and screened in seven weeks. Screening was accomplished by subdividing primary transformation plates into pools of approximately 100 clones which were transferred into a master glycerol stock. These master stocks were used to inoculate liquid cultures to produce culture "pools," and ten pools of 100 clones were then combined to yield superpools of 1,000 clones. Both pool and superpool DNA was screened by polymerase chain reaction (PCR) and positive pools representing 100 clones were then plated on selective medium and screened by in situ hybridization. Screening by the two tiered PCR assay and by in situ hybridization was completed in 4-5 days. Utilizing this methodology we have isolated a 150 kb clone spanning the alpha 1(I) collagen (Col1a1) gene as well as 40 kb clones from the Hox-2 locus. To characterize the representation of the YAC library, the size distribution of genomic Sal I fragments was compared to that of clones picked at random from the library. The results demonstrate significant biasing of the cloned fragment distribution, resulting in a loss of representation for larger fragments.

Base Sequence↗
PubMed1992

Infection by polyomavirus of murine cells deficient in class I major histocompatibility complex expression.

Embryonic fibroblasts and kidney epithelial cells from beta 2-microglobulin-deficient mice were as infectible by polyomavirus as cells from normal littermates were, as judged by expression of nuclear viral capsid antigen, development of cytopathic effects, and yields of infectious virus. We conclude that expression of intact class I major histocompatibility complex molecules is not essential for polyomavirus infection.

Animals↗
PubMed1992

An X-linked human collagen transgene escapes X inactivation in a subset of cells.

Transgenic mice carrying one complete copy of the human alpha 1(I) collagen gene on the X chromosome (HucII mice) were used to study the effect of X inactivation on transgene expression. By chromosomal in situ hybridization, the transgene was mapped to the D/E region close to the Xce locus, which is the controlling element. Quantitative RNA analyses indicated that transgene expression in homozygous and heterozygous females was about 125% and 62%, respectively, of the level found in hemizygous males. Also, females with Searle's translocation carrying the transgene on the inactive X chromosome (Xi) expressed about 18% transgene RNA when compared to hemizygous males. These results were consistent with the transgene being subject to but partially escaping from X inactivation. Two lines of evidence indicated that the transgene escaped X inactivation or was reactivated in a small subset of cells rather than being expressed at a lower level from the Xi in all cells, (i) None of nine single cell clones carrying the transgene on the Xi transcribed transgene RNA. In these clones the transgene was highly methylated in contrast to clones carrying the transgene on the Xa. (ii) In situ hybridization to RNA of cultured cells revealed that about 3% of uncloned cells with the transgene on the Xi expressed transgene RNA at a level comparable to that on the Xa. Our results indicate that the autosomal human collagen gene integrated on the mouse X chromosome is susceptible to X inactivation. Inactivation is, however, not complete as a subset of cells carrying the transgene on Xi expresses the transgene at a level comparable to that when carried on Xa.

Animals↗
PubMed1992

Site-directed mutagenesis of type I collagen: effect on susceptibility to collagenase.

A genetic approach to define the role of collagenase in physiological and pathological bone remodeling is to identify spontaneous mutations in the collagenase gene which alter enzymatic activity. Alternatively it is possible, though site-directed mutagenesis, to alter genes encoding critical amino acid sequences in the collagen substrate, in a manner analogous to the successful development of animal models for osteogenesis imperfecta. We have thus utilized this approach to alter the Col1a1 gene to encode amino acid substitutions in sequences around the known collagenase cleavage site (glycine-isoleucine at positions 775-776) in type I collagen, and transfect these genes into homozygous Mov-13 fibroblasts, in which the endogenous Col1a1 gene is inactive. Nonconservative substitutions of proline for isoleucine at the P1' site and double substitutions of proline for glutamine (P2) and alanine (P2') resulted in type I collagen resistant to hydrolysis by collagenase. Furthermore, in normal fibroblasts transfected with a mutant Col1a1 gene encoding collagenase resistance in which an additional methionine substitution at position 776 provided a marker for the mutant protein, mutant and wild type triple helical molecules were synthesized and secreted as heterotrimers. A single mutant alpha 1(I) chain did not prevent cleavage of the wild type alpha 1(I) chain but it is likely that the uncleaved alpha 1(I) chain would prevent dissociation of the triple helical fragments containing the other cleaved chains. Introduction of these genes into transgenic mice should result in abnormal phenotypes characterized by altered connective tissue remodeling.

Amino Acid Sequence↗
PubMed1991

Clearance of influenza virus respiratory infection in mice lacking class I major histocompatibility complex-restricted CD8+ T cells.

Transgenic mice homozygous for a beta 2-microglobulin (beta 2-m) gene disruption and normal mice that had been treated with a CD8-specific mAb were infected intranasally with an H3N2 influenza A virus. Both groups of CD8T cell-deficient mice eliminated the virus from the infected respiratory tract. Potent CTL activity was detected in lung lavage populations taken from mice with intact CD8+ T cell function, with minimal levels of cytotoxicity being found for inflammatory cells obtained from the antibody-treated and beta 2-m mutant mice. We therefore conclude that cells infected with an influenza A virus can be cleared from the respiratory tract of mice lacking both functional class I major histocompatibility complex (MHC) glycoproteins and class I MHC-restricted, CD8+ effector T cells.

Animals↗
PubMed1991

MHC class I deficiency: susceptibility to natural killer (NK) cells and impaired NK activity.

The role of major histocompatibility complex (MHC) class I expression in natural killer (NK) cell target recognition is controversial. Normal T cell blasts from MHC class I-deficient mutant mice were found to serve as target cells for NK cells in vitro, which suggests that MHC class I molecules are directly involved in NK cell recognition. Spleen cells from the mutant mice were deficient in their ability to lyse MHC class I-deficient target cells or NK-susceptible tumor targets, and mutant mice could not reject allogeneic bone marrow. Thus, class I molecules may participate in the positive selection or tolerance induction of NK cells.

Animals↗
PubMed1991

Cellular transcripts encoded at a locus which permits retrovirus expression in mouse embryonic cells.

Three independent recombinant retroviruses have been activated on insertion into the F2 locus of mouse F9 embryonal carcinoma cells. Each provirus has integrated downstream from the cellular F2 promoter, which is active in transient transfection assays using a chloramphenicol acetyltransferase reporter enzyme. The F2 promoter drives expression of a series of related transcripts in F9 and 3T3 cells, and a single 450-nt transcript in mouse tissues. F2 homologous sequences have been detected in the genomes of all mammalian species tested, and the 450-nucleotide (nt) F2 transcript is expressed in rat and human cells. Three pairs of differently sized F2 cDNA clones have been isolated and analyzed. The largest clones possess two 199-nt 98.5% identical repeats, one of which is present in the smaller clones, as well as the major 450-nt transcript. Activated proviral integration sites map to introns of the largest F2 cDNA clone. While none of the F2 cDNA contains a long open reading frame or homology to databank sequences, evidence suggests that the F2 locus encodes a constitutive function required at high levels, or represents an expressed but nonfunctional, single-copy element, conserved among mammals.

Animals↗
PubMed1991

Involvement of the cell cycle-regulated nuclear factor HiNF-D in cell growth control of a human H4 histone gene during hepatic development in transgenic mice.

Regulation of the cell cycle-controlled histone gene promoter factor HiNF-D was examined in vivo. Proliferative activity was measured by DNA replication-dependent histone mRNA levels, and HiNF-D binding activity was found to correlate with cell proliferation in most tissues. Furthermore, HiNF-D is down-regulated during hepatic development, reflecting the onset of differentiation and quiescence. The contribution of transcription to histone gene expression was directly addressed in transgenic mice by using a set of fusion constructs containing a human H4 histone gene promoter linked to three different genes. Transgene expression in both fetal and adult mice paralleled endogenous mouse histone mRNA levels in most tissues, consistent with this promoter conferring developmental, cell growth-related transcriptional regulation. Our results suggest that HiNF-D is stringently regulated in vivo in relation to cell growth and support a primary role for HiNF-D in the proliferation-specific expression of H4 histone genes in the intact animal. Further, the data presented here provide an example in which apparent tissue specificity of gene expression reflects the proliferative state of various tissues and demonstrate that multiple levels of histone gene regulation are operative in vivo.

Aging↗
PubMed1991

Rejection of class I MHC-deficient haemopoietic cells by irradiated MHC-matched mice.

Irradiated MHC-heterozygous mice often reject bone marrow cells transplanted from one of the homozygous parental strains, a phenomenon ('hybrid resistance') that appears to violate the laws of transplantation. Rejection of parental and allogeneic marrow cells also differs from conventional T cell-mediated rejection mechanisms as it is effected by NK1.1+ cells. To account for the unusual specificity of bone marrow rejection, it has been proposed that NK1.1+ cells destroy marrow cells that fail to express the full complement of self MHC class I (MHC-I) molecules. We show here that NK1.1+ cells in normal mice reject haemopoietic transplants from mice that are deficient for normal cell-surface MHC-I expression because of a targeted mutation in the beta 2-microglobulin gene. These findings demonstrate that deficient expression of MHC-I molecules renders marrow cells susceptible to rejection.

Animals↗
PubMed1991

The recombination activating gene-1 (RAG-1) transcript is present in the murine central nervous system.

The recombination activating genes, RAG-1 and RAG-2, are likely to encode components of the V(D)J site-specific recombination machinery. We report here the detection of low levels of the RAG-1 transcript in the murine central nervous system by polymerase chain reaction, in situ hybridization, and Northern blot analyses. In contrast, an authentic RAG-2 transcript could not be detected reproducibly in the central nervous system. The RAG-1 transcript was found to be widespread in embryonic and postnatal neurons, with transcription being most apparent in regions of the postnatal brain with a high neuronal cell density (the cerebellum and the hippocampal formation). The results suggest that RAG-1 functions in neurons, where its role might be to recombine elements of the neuronal genome site-specifically, or to prevent detrimental alterations of the genome in these long-lived cells.

Aging↗
PubMed1991

The murine Mov-34 gene: full-length cDNA and genomic organization.

The Mov-34 mutation is a recessive embryonic lethal mutation caused by experimental introduction of a recombinant Moloney murine leukemia provirus into the mouse germline. We have cloned a full-length cDNA from the Mov-34 gene, the transcription unit disrupted by the proviral integration. This cDNA is predicted to encode a novel 321-amino acid, 36-kDa protein of unknown function. Overlapping phage lambda clones containing the entire Mov-34 gene have been isolated. The Mov-34 gene spans just over 8 kb and contains seven exons. The 5' flanking region of the Mov-34 gene contains neither "TATA" nor "CAAT" box sequences, and 5' end mapping by primer extension and ribonuclease protection reveal multiple transcription initiation sites.

Amino Acid Sequence↗
PubMed1991

Retrovirus-induced insertional mutagenesis: mechanism of collagen mutation in Mov13 mice.

The Mov13 mouse strain carries a mutation in the alpha 1(I) procollagen gene which is due to the insertion of a Moloney murine leukemia provirus into the first intron. This insertion results in the de novo methylation of the provirus and flanking DNA, the alteration of chromatin structure, and the transcriptional inactivity of the collagen promoter. To address the mechanism of mutagenesis, we reintroduced a cloned and therefore demethylated version of the Mov13 mutant allele into mouse fibroblasts. The transfected gene was not transcribed, indicating that the transcriptional defect was not due to the hypermethylation. Rather, this result strongly suggests that the mutation is due to the displacement or disruption of cis-acting regulatory DNA sequences within the first intron. We also constructed a Mov13 variant allele containing a single long terminal repeat instead of the whole provirus. This construct also failed to express mRNA, indicating that the Mov13 mutation does not revert by provirus excision as has been observed for other retrovirus-induced mutations.

Alleles↗
PubMed1991

A generic intron increases gene expression in transgenic mice.

To investigate the role of splicing in the regulation of gene expression, we have generated transgenic mice carrying the human histone H4 promoter linked to the bacterial gene for chloramphenicol acetyltransferase (CAT), with or without a heterologous intron in the transcription unit. We found that CAT activity is 5- to 300-fold higher when the transgene incorporates a hybrid intron than with an analogous transgene precisely deleted for the intervening sequences. This hybrid intron, consisting of an adenovirus splice donor and an immunoglobulin G splice acceptor, stimulated expression in a broad range of tissues in the animal. Although the presence of the hybrid intron increased the frequency of transgenics with significant CAT activity, it did not affect the integration site-dependent variation commonly seen in transgene expression. To determine whether the enhancement is a general outcome of splicing or is dependent on the particular intron, we also produced equivalent transgenics carrying the widely used simian virus 40 small-t intron. We found that the hybrid intron is significantly more effective in elevating transgene expression. Our results suggest that inclusion of the generic intron in cDNA constructs may be valuable in achieving high levels of expression in transgenic mice.

Animals↗
PubMed1991

Migration and proliferation of cultured neural crest cells in W mutant neural crest chimeras.

Chimeric mice, generated by aggregating preimplantation embryos, have been instrumental in the study of the development of coat color patterns in mammals. This approach, however, does not allow for direct experimental manipulation of the neural crest cells, which are the precursors of melanoblasts. We have devised a system that allows assessment of the developmental potential and migration of neural crest cells in vivo following their experimental manipulation in vitro. Cultured C57Bl/6 neural crest cells were microinjected in utero into neurulating Balb/c or W embryos and shown to contribute efficiently to pigmentation in the host animal. The resulting neural crest chimeras showed, however, different coat pigmentation patterns depending on the genotype of the host embryo. Whereas Balb/c neural crest chimeras showed very limited donor cell pigment contribution, restricted largely to the head, W mutant chimeras displayed extensive pigmentation throughout, often exceeding 50% of the coat. In contrast to Balb/c chimeras, where the donor melanoblasts appeared to have migrated primarily in the characteristic dorsoventral direction, in W mutants the injected cells appeared to migrate in the longitudinal as well as the dorsoventral direction, as if the cells were spreading through an empty space. This is consistent with the absence of a functional endogenous melanoblast population in W mutants, in contrast to Balb/c mice, which contain a full complement of melanocytes. Our results suggest that the W mutation disturbs migration and/or proliferation of endogenous melanoblasts. In order to obtain information on clonal size and extent of intermingling of donor cells, two genetically marked neural crest cell populations were mixed and coinjected into W embryos. In half of the tricolored chimeras, no co-localization of donor crest cells was observed, while, in the other half, a fine intermingling of donor-derived colors had occurred. These results are consistent with the hypothesis that pigmented areas in the chimeras can be derived from extensive proliferation of a few donor clones, which were able to colonize large territories in the host embryo. We have also analyzed the development of pigmentation in neural crest cultures in vitro, and found that neural tubes explanted from embryos carrying wt or weak W alleles produced pigmented melanocytes while more severe W genotypes were associated with deficient pigment formation in vitro.

Animals↗
PubMed1991

Generation of pigmented stripes in albino mice by retroviral marking of neural crest melanoblasts.

The pigment cells of the skin are derived from melanoblasts which originate in the neural crest. The dorsoventral migration of melanoblasts has been visualized in pigment stripes seen in aggregation chimeras, and the width of these bands has suggested that the entire pigmentation of the coat is derived from a small number of founder cells. We have generated mosaic mice by marking single melanoblasts in utero to gain information on the clonal history of pigment-forming cells. A retroviral vector carrying the human tyrosinase gene was constructed and microinjected into neurulating albino mouse embryos. Albino mice are devoid of pigmentation due to deficiency of tyrosinase. Thus, transduction of the wild-type gene into the otherwise normal melanoblasts should rescue the mutant phenotype, giving rise to patches of pigmentation, which correspond to the area colonized by the mitotic progeny of a marked clone. Mosaic animals derived from the injected embryos indeed showed pigmented bands with a width strikingly similar to the 'standard' stripes seen in aggregation chimeras. These results are consistent with the notion that the unit width bands seen in aggregation chimeras represent the clonal progeny of a single melanoblast and verify Mintz's (1967) conclusion that a few founder melanoblasts give rise to coat pigmentation. The pigment cells of the eye are of dual origin: the melanocytes in choroid and outer layer of the iris are derived from the neural crest and those in the pigment layer of the retina from the neuroepithelium of the optic cup. Marked clones in both lineages were observed in the eyes of many mosaic animals.

Animals↗