Maternal-fetal tolerance is maintained despite transgene-driven trophoblast expression of MHC class I, and defects in Fas and its ligand

During mammalian pregnancy, one or more semiallogeneic fetuses gestate in direct contact with the maternal circulation and uterine tissue. However, a damaging maternal immune response is not normally provoked. We studied two possible mechanisms for this maternal-fetal tolerance, alone and in combination. First, we directly tested the hypothesis that the striking absence of MHC class I molecules on most placenta trophoblasts protects the fetus from maternal immune attack, by creating transgenic mice which express Ld in giant cell trophoblasts. Second, because Fas ligand (FasL) may contribute to immune privilege, we tested whether functional FasL expression by the fetus, or Fas expression by the mother, contributes to successful reproduction in a fully allogeneic breeding. Our data indicate that neither abnormal expression of MHC class I in giant cells, nor disruption of the Fas-FasL system, nor a combination of these two defects, has an adverse effect on pregnancy outcome. These results suggest that during healthy allogeneic pregnancy, down-regulation of MHC class I and expression of FasL on placenta are not critical events, and other factors must prevent a harmful maternal immune response.

Peptide ligand structure influences the exchange of beta2-microglobulin by cell surface Kb

We have studied the interactions which occur between the peptide ligand and beta2-microglobulin (beta2m) components of the class I MHC complex by analysing the process of beta2m exchange. We have previously shown that the rate of beta2m exchange on a cell-surface class I MHC complex varies with the peptide ligand to which it is bound. It remains unclear, however, whether the ability of peptide ligand to alter beta2m/heavy-chain association is related to peptide affinity, peptide structure, or both. In this article, we examine the effects of variations in peptide ligand structure on the rate of beta2m exchange by cell surface Kb complexes. Using a panel of alanine substituted variants of the MCMV peptide (YPHFMPTNL), we show that single amino acid changes in peptide sequence can have dramatic effects on the rates of beta2m exchange. The observed changes in beta2m exchange rates are directly due to modification of the peptide ligand structure as they do not reflect changes in peptide affinity. These findings suggest that peptide ligand structure can induce conformational changes in the Kb heavy chain which alter the rates of cell surface beta2m exchange, and provide further evidence for peptide-dependent fluidity of the class I heavy chain.

Effects of adenosine on retrograde refractoriness of accessory atrioventricular connections

Ventricular premature stimuli were used to demonstrate adenosine-mediated decreases in the retrograde refractoriness of accessory atrioventricular connections. This response is consistent with the concept that accessory atrioventricular connections have electrophysiologic properties that are similar to those of atrial myocardium.

Influence of the preoperative signal-averaged electrocardiogram on left ventricular function after coronary artery bypass graft surgery in patients with left ventricular dysfunction. The CABG Patch Trial

Patients with ischemic left ventricular (LV) dysfunction often have an improved survival and life quality after coronary artery bypass grafting (CABG), in part due to an improvement in LV function. A lack of LV ejection fraction (EF) improvement postoperatively portends a worse prognosis. Recently, an abnormal preoperative signal-averaged electrocardiogram (SAECG) in patients with a severely depressed LV ejection fraction undergoing elective CABG was shown to be associated with a higher early and late postoperative mortality. The present study evaluated patients with severe LV dysfunction to identify any relation between an abnormal preoperative SAECG and postoperative changes in LV function after successful CABG. Forty-five patients with LV dysfunction (LVEF <0.36) scheduled for elective CABG underwent preoperative SAECG and both pre- and postoperative LVEF determinations using radionuclide scans. Thirty-one patients in the group had an abnormal preoperative SAECG and 14 patients had a normal preoperative SAECG. Baseline patient characteristics were similar in both groups and the mean preoperative LVEF was 0.26. Overall, LVEF improved 31% postoperatively with a significantly greater benefit noted in the group with a normal baseline SAECG (14.9+/-5.7-point vs 4.8+/-8.5-point increase, p <0.001). All patients whose LVEF did not improve or worsened postoperatively had an abnormal preoperative SAECG. No SAECG measure was altered significantly by the operation. A preoperative SAECG provides information on the postoperative functional recovery of ischemic myocardium.

Proteolytic mechanisms in corneal ulceration and repair

Corneal stromal ulceration is a devastating disorder that can cause blindness. Stromal ulceration was once thought to be a physical dissolution process, which even now is described as "melting." However, a major paradigm change occurred about 25 years ago with the demonstration of extracellular matrix-degrading activity associated with tissues isolated from ulcerating corneas. Recent studies have identified the enzymes involved as specific members of the matrix metalloproteinase (MMP) family. These studies have further provided evidence that MMPs participate at all stages of the ulcerative process, from formation of the initiating epithelial defect to ulcer resolution and repair. Roles for MMPs in these processes are discussed in this review. Studies on corneal ulceration provide basic information about failure to heal, which is useful for understanding mechanisms common to other organ systems besides the cornea.

The role of engineering geology in the hazard zonation of a Malaysian highway

The University of Strathclyde and the Institut Kerja Raya Malaysia (Public Works Institute) have undertaken a joint research project into the investigation, description, classification and geotechnical analysis of tropically weathered in situ materials (TWIMs) in Malaysia in general and on a major highway in particular. The research project has developed a general approach to TWIM profile characterization and classification which allows specific systems to be developed to deal with particular project requirements.

A key part of the research is to provide practical engineering geological and geotechnical advice to a hazard identification and risk assessment project on the 113 km long East-West Highway in Kelantan, northern Peninsular Malaysia. This highway has an ongoing history of persistant slope failure and contains a large number of significant earthworks in generlly mountainous terrain underlain by a ange of tropically weathered bedrocks including sedimentary, meta-sedimentary and igneous materials. The 3-year long-term project produced hazard maps for the earthworks along the highway. These maps provided a more scientific basis for cost-effective planning and design of maintenance and preventative remedial works along the highway.

This paper outlines the main elements of the project and indicates the key influence that the engineering geological character of the tropically weahered soil-rock profiles has had on the assessment of slope hazard.

Role of serum amyloid A as an intermediate in the IL-1 and PMA-stimulated signaling pathways regulating expression of rabbit fibroblast collagenase

The matrix metalloproteinase collagenase is expressed by resident tissue cells only when needed for biological remodeling. Exogenous addition of inflammatory and growth-promoting cytokines stimulates collagenase expression in early passage fibroblast cultures. In addition, the signal for collagenase expression in response to phorbol-12 myristate-13 acetate (PMA) or to agents which alter cell shape in early passage fibroblast cultures is routed extracellularly to an autocrine cytokine intermediate, IL-1 alpha. Importantly, fibroblasts, when freshly isolated from the tissue, are not competent for IL-1 alpha gene expression and, therefore, cannot produce collagenase in response to shape change agents. However, they do make a small amount of collagenase in response to PMA via an IL-1-independent pathway that has not been further characterized. In this paper, we investigate the role of a second autocrine, serum amyloid A3 (SAA3), in IL-1-dependent and -independent collagenase gene expression. We demonstrate that SAA3 is required for effective stimulation of collagenase expression by either exogenous or endogenous IL-1. Furthermore, while freshly isolated fibroblasts cannot express IL-1 alpha they can express SAA3, and this autocrine mediator acts independently of IL-1 alpha to control the low level of collagenase expression that can be stimulated by PMA. These results provide further evidence for a newly emerging paradigm of collagenase regulation which emphasizes the requirement for extracellular routing of signals. They also suggest that SAA3 might be utilized independently of IL-1 alpha to control tissue remodeling in vivo.

The interferon gamma (IFN-gamma) receptor: a paradigm for the multichain cytokine receptor

With the purification and cloning of the interferon gamma (IFN-gamma) receptor chains the mechanism of IFN-gamma action and the resultant signal transduction events were delineated in remarkable detail. The interferon gamma (IFN-gamma) receptor complex consists of two chains: IFN-gammaR1, the ligand-binding chain, and IFN-gammaR2, the accessory chain. Binding of IFN-gamma causes oligomerization of the two IFN-gamma receptor subunits, IFN-gammaR1 and IFN-gammaR2, which initiates the signal transduction events: activation of Jak1 and Jak2 receptor associated protein tyrosine kinases, phosphorylation of the IFN-gammaR1 intracellular domain on Tyr440 followed by phosphorylation and activation of Stat1alpha, the latent transcriptional factor. With all these steps established, the IFN-gamma receptor complex has provided the basic model for understanding the receptors for other members of the family of class II cytokine receptors.

A double-label technique that monitors sulfur mustard damage to nuclei and mitochondria of normal human epidermal keratinocytes in vitro

Sulfur mustard and 2-chloro ethyl ethyl sulfide (CEES, a sulfur mustard analog) is known to have immediate (minutes), long-term (hours to days), and toxic effects on human skin. Research was directed toward developing a single in vitro assay that might reflect both these short-term and long-term effects of this vesicating agent on normal human epidermal keratinocytes (NHEK) in vitro. Such an assay system would be useful in identifying and developing sulfur mustard therapeutic agents. NHEK were exposed to the monofunctional sulfur mustard analog 2-chloro ethyl ethyl sulfide for a variety of times. The effects of CEES on NHEK nuclei were assessed using the membrane-permeable SYTO nuclear stains, whereas the effects of CEES on NHEK metabolism were determined by using the nontoxic mitochondria dye Alamar blue. CEES enhanced SYTO binding in a concentration-dependent manner to the nucleus immediately subsequent to a 2-hr exposure, whereas CEES had relatively little effect on metabolic activity at this time. Fifteen to 36 hr subsequent to CEES exposure, however, Alamar blue revealed a robust, sulfur mustard-dependent effect on mitochondrial activity. To determine if both these indicator dyes could be used simultaneously, NHEK were exposed to CEES and stained with the SYTO nuclear stain 2 hr subsequent to exposure. This procedure was followed by assay of the same cell cultures with Alamar blue at 36 hr subsequent to initial CEES exposure. The data indicate that this nuclear/mitochondrial double-label technique can be used to monitor the short- and long-term effects of sulfur mustard on the same culture of NHEK.

Quantitation of the cell surface level of Ld resulting in positive versus negative selection of the 2C transgenic T cell receptor in vivo

The 2C transgenic TCR is positively selected on Kb and is alloreactive for and negatively selected on Ld. To test an avidity model for positive selection, mice were bred to express different levels of surface Ld by varying the number of gene copies encoding beta 2-microglobulin (beta 2m) or Ld heavy chain. Whereas mice expressing 35% Ld (beta 2m+/- Ld+/-) negatively selected the 2C TCR, mice expressing 2% Ld (beta 2m-/- Ld+/-) positively selected the 2C TCR. Furthermore, 2C cytotoxic T lymphocytes selected on 2% Ld showed peptide-specific cytolytic activity against Ld/p2Ca targets. These findings provide clear in vivo evidence that positive selection can occur on very low levels of the same class I antigen capable of negative selection when expressed at higher levels.

Neighbors' perceptions of group homes

Neighbors often presume that group homes (GHs) have negative effects on their neighborhoods, but it is rather unclear how often GHs actually have adverse effects. Neighbors of GHs and a matched set of people who did not live near GH were interviewed. Neighbors of GHs were asked about their experiences with the specific GH near them, while "non-neighbors" were asked similar questions about their expectations of what it would be like to live near a GH. For both negative (e.g., noise, traffic) and positive effects (e.g., leaning about disabilities) of GHs, non-neighbors expected GHs would have a much greater impact on them than what was actually reported by neighbors. This research supports prior findings that expectations of negative effects are much greater than what is actually experienced by neighbors. It also suggests that GH operators might wish to capitalize on the positive expectations that may be over-shadowed by the more commonly voiced negative expectations.

Mouse macrophages carrying both subunits of the human interferon-gamma (IFN-gamma) receptor respond to human IFN-gamma but do not acquire full protection against viral cytopathic effect

Studies of hamster-human and mouse-human somatic fibroblast hybrids and transfected mouse fibroblasts have demonstrated that signaling through the human interferon-gamma receptor (hu-IFN-gammaR) requires the formation of a complex consisting of ligand (IFN-gamma), a ligand binding receptor chain (IFN-gammaR1), and a signal transducing receptor chain (IFN-gammaR2). To date, the ability of this receptor complex to transduce the full repertoire of biological signals has been difficult to assess due to the limited number of activities that IFN-gamma can exert on fibroblasts. The current report assesses the ability of hu-IFN-gammaR chains to transduce signals in the absence of background human gene products by expressing hu-IFN-gammaR2 in a transformed macrophage cell line (F10/96) derived from a hu-IFN-gammaR1 transgenic mouse. Our results indicate that F10/96 clones expressing both human receptor proteins bind hu-IFN-gamma with an affinity comparable to that of human cells. Binding of either human or mouse IFN-gamma to its respective receptor elicits classic IFN-gamma responses such as up-regulation of major histocompatibility complex antigens, enhanced expression of IRF-1, and increased production of NO2- radicals, interleukin-6, tumor necrosis factor-alpha, and granulocyte macrophage-colony stimulating factor. However, hu-IFN-gamma could not fully protect the clones from cytopathic effects of encephalomyocarditis virus and vesicular stomatitis virus while mo-IFN-gamma could. These results demonstrate that while co-expression of hu-IFN-gammaR1 and hu-IFN-gammaR2 is necessary and sufficient for most IFN-gamma-induced responses, it is not sufficient to confer a generalized antiviral state. These findings further suggest that additional species-specific accessory factor(s) are necessary for full signaling potential through the IFN-gamma receptor complex. The nature and potential role of such factors in IFN-gammaR signaling is discussed.

Effects of adenosine on wavelength of premature atrial complexes in patients without structural heart disease

Intravenous adenosine produced slight decreases in conduction times for premature atrial complexes but proportionally greater shortening of the functional refractory period. Decreased wavelength may provide a basis for transient atrial fibrillation, which is sometimes observed after adenosine administration.

Role of matrix metalloproteinases in failure to re-epithelialize after corneal injury

Delayed re-epithelialization of the cornea after injury usually precedes stromal ulceration. Previous findings using a rat thermal injury model suggested that re-epithelialization is impeded by products of resident corneal cells, which destroy adhesive structures at the basement membrane zone. In this study, we provide additional evidence for this concept. Failure to re-epithelialize was found to correlate with an increase in the amounts of gelatinolytic matrix metalloproteinases present in the rat cornea. One of these gelatinases, gelatinase B, is synthesized by the resident corneal cells, and inhibitions of its synthesis correlated with inhibition of basement membrane dissolution. The matrix metalloproteinases collagenase and stromelysin are also synthesized by resident corneal cells in thermally injured corneas of rabbits, but the timing of bulk enzyme synthesis correlated more closely with deposition of repair tissue in the stroma than with failure to re-epithelialize. Nevertheless, in human corneas with repair defects, gelatinase B and collagenase are synthesized by cells in the basal layer of the epithelium directly adjacent to the basement membrane, suggesting that both could participate in dissolution of this structure. Importantly, treatment of thermally injured corneas with a synthetic inhibitor of matrix metalloproteinases significantly improved basement membrane integrity. These data support the concept that over-expression of matrix metalloproteinases by resident corneal cells impedes re-epithelialization after some types of corneal injury.

The mechanisms of peptide exchange and beta 2-microglobulin exchange on cell surface Ld and Kb molecules are noncooperative

It has previously been shown that the presence of exogenous beta 2-microglobulin (beta 2m) can dramatically enhance the binding of exogenous peptide to cell surface class I MHC. However, the mechanism by which this enhancement takes place is unknown. Two models have been proposed to explain this phenomenon. In the first model, the exchange of peptide and the exchange of beta 2m are cooperative processes. In the alternative model, beta 2m stabilizes free class I heavy chains to increase the total number of peptide binding sites available. In this report, we have examined the relationship between peptide exchange and beta 2m exchange. Comparisons of Ld and Kb complexes formed with peptides possessing widely disparate affinities revealed a reciprocal correlation between the peptide off-rate and the rate of beta 2m exchange. This result indicates that peptide exchange and beta 2m exchange are noncooperative processes that may, in fact, antagonize one another. These findings provide the first demonstration of peptide-specific influences on the rate of beta 2m exchange and suggest that exogenous beta 2m promotes peptide binding by maintaining class I heavy chains in a peptide-receptive state.

The mechanisms of peptide exchange and beta 2-microglobulin exchange on cell surface Ld and Kb molecules are noncooperative

It has previously been shown that the presence of exogenous beta 2-microglobulin (beta 2m) can dramatically enhance the binding of exogenous peptide to cell surface class I MHC. However, the mechanism by which this enhancement takes place is unknown. Two models have been proposed to explain this phenomenon. In the first model, the exchange of peptide and the exchange of beta 2m are cooperative processes. In the alternative model, beta 2m stabilizes free class I heavy chains to increase the total number of peptide binding sites available. In this report, we have examined the relationship between peptide exchange and beta 2m exchange. Comparisons of Ld and Kb complexes formed with peptides possessing widely disparate affinities revealed a reciprocal correlation between the peptide off-rate and the rate of beta 2m exchange. This result indicates that peptide exchange and beta 2m exchange are noncooperative processes that may, in fact, antagonize one another. These findings provide the first demonstration of peptide-specific influences on the rate of beta 2m exchange and suggest that exogenous beta 2m promotes peptide binding by maintaining class I heavy chains in a peptide-receptive state.

Differential responsiveness of a splice variant of the human type I interferon receptor to interferons

Chinese hamster ovary cells containing the yeast artificial chromosome F136C5 (alphaYAC) respond to all type I human interferons including IFN-alphaA, IFN-beta, and IFN-omega. The alphaYAC contains at least two genes encoding interferon-alpha receptor (IFN-alphaR) chains that are required for response to type I human interferons: Hu-IFN-alphaR1 and Hu-IFN-alphaR2. We previously isolated a splice variant of the Hu-IFN-alphaR1 chain designated Hu-IFN-alphaR1s. Chinese hamster ovary cells containing a disrupted alphaYAC, which contains a deletion in the human IFNAR1 gene, were transfected with expression vectors for the Hu-IFN-alphaR1 and Hu-IFN-alphaR1s chains. With these cells, two type I interferons have been identified which can interact with the splice variant (Hu-IFN-alphaR1s) and with the Hu-IFN-alphaR1 chains: Hu-IFN-alphaA and IFN-omega. Two other type I interferons, Hu-IFN-alphaB2 and Hu-IFN-alphaF, are capable of signaling through the Hu-IFN-alphaR1 chain only and cannot utilize the splice variant Hu-IFN-alphaR1s. Hu-IFN-alphaR1 and Hu-IFN-alphaR1s differ in that the latter is missing a single subdomain of the receptor extracellular domain encoded by exons 4 and 5 of the IFNAR1 gene. These results therefore indicate that different type I interferons require different subdomains of the Hu-IFN-alphaR1 receptor chain, and that the splice variant chain (Hu-IFN-alphaR1s) is functional.

Disruption of microfilaments alters laminin synthesis but not laminin trafficking in NHEK in vitro

Laminin synthesis and deposition are concomitant with the development of a basal lamina between the human epidermis and the underlying dermis. One of the challenges in tissue engineering of human epidermal models is to develop substrates and conditions that encourage the development of a basement membrane. The purpose of this study was to determine if actin filaments and/or microtubules are involved in the synthesis/secretion of laminin by normal human epidermal keratinocytes (NHEK) in vitro. NHEK synthesize and secrete laminin subunits B1, B2, and M but little, if any, of laminin subunit A. Data indicate that disruption of microfilaments by the destabilizing agent, cytochalasin D, had no apparent effect on the relative synthesis rates of most cytosolic proteins as revealed by one-dimensional sodium dodecyl sulfate (SDS) gel electrophoresis. This drug, however, increased laminin B2 synthesis several fold over untreated controls. This enhanced synthetic rate was independent of the type of collagen matrix on which the NHEK were grown. Similar increases in synthesis of the M and B1 laminin chains were not observed. To determine if this increase in synthesis lead to increases in laminin B2 secretion, laminin B2 was immunoprecipitated from both the apical and basal domains of NHEK cells grown on microporous membranes. While more laminin B1, B2, and M were secreted basally than apically, an observation consistent with laminin's role in basal lamina formation, cytochalasin D had no apparent effect on either basal or apical laminin B2 secretion. Experiments with the microtubule destabilizer, nocodazole, showed no similar effects on laminin synthesis and/or secretion. We conclude that (a) disruption of the actin network in NHEK selectively increases the synthesis of laminin B2, (b) the secretion of laminin B2 from NHEK cells is not governed by either the microfilamentous cytoskeleton or the amount of laminin synthesized by NHEK, and (c) disruption of the microtubular network does not alter laminin synthesis or secretion.

Interferon-gamma differentially regulates antigen-processing functions in distinct endocytic compartments of macrophages with constitutive expression of class II major histocompatibility complex molecules

RAW264.7 cells were transfected to express constitutively the murine class II major histocompatibility complex (MHC-II) molecule, I-Ak. The resulting RAW.Ak cells presented HEL(46-61) peptide to 3A9 T hybridoma cells, but they were unable to process and present HEL protein in their resting state. However, IFN-gamma stimulation induced the ability of RAW.Ak to process and present HEL protein, with little effect on their ability to present HEL(46-61) peptide. Antigen catabolism showed little change with IFN-gamma stimulation, suggesting that the production of peptides was not the regulated step in the processing pathway. Furthermore, HEL(46-61) peptide delivered directly into lysosomes by acid-resistant liposomes was also presented only upon IFN-gamma stimulation, while the presentation of peptides delivered into endosomes by acid-sensitive liposomes showed a lesser dependence on IFN-gamma stimulation. Thus, IFN-gamma regulated the ability of peptides delivered into certain lysosomal compartments to meet with MHC-II molecules and form peptide-MHC complexes, or to transport subsequently to the plasma membrane. Two other antigens, ribonuclease A and haemoglobin, were processed by RAW.Ak cells without IFN-gamma stimulation, suggesting that these antigens could be processed by different mechanisms, perhaps in earlier endocytic compartments. Thus, different antigens may be processed in distinct endocytic compartments, and an IFN-gamma-regulated mechanism controls the rescue of peptides from lysosomal compartments for presentation at the plasma membrane.

Interaction between the components of the interferon gamma receptor complex

Interferon gamma (IFN-gamma) signals through a multimeric receptor complex consisting of two different chains: the IFN-gamma receptor binding subunit (IFN-gamma R, IFN-gamma R1), and a transmembrane accessory factor (AF-1, IFN-gamma R2) necessary for signal transduction. Using cell lines expressing different cloned components of the IFN-gamma receptor complex, we examined the function of the receptor components in signal transduction upon IFN-gamma treatment. A specific IFN-gamma R2:IFN-gamma cross-linked complex was observed in cells expressing both IFN-gamma R1 and IFN-gamma R2 indicating that IFN-gamma R2 (AF-1) interacts with IFN-gamma and is closely associated with IFN-gamma R1. We show that the intracellular domain of IFN-gamma R2 is necessary for signaling. Cells coexpressing IFN-gamma R1 and truncated IFN-gamma R2, lacking the COOH-terminal 51 amino acids (residues 286-337), or cells expressing IFN-gamma R1 alone were unresponsive to IFN-gamma treatment as measured by MHC class I antigen induction. Jak1, Jak2, and Stat1 alpha were activated, and IFN-gamma R1 was phosphorylated only in cells expressing both IFN-gamma R1 and IFN-gamma R2. Jak2 kinase was shown to associate with the intracellular domain of the IFN-gamma R2.

Conformational changes induced in the MHC class I molecule by peptide and beta 2-microglobulin

Assembly of the class I MHC molecule is inextricably linked to the antigen presentation function of the class I molecule. Association of the class I MHC molecule with beta 2-microglobulin (beta 2m) is a prerequisite for association with the heterodimeric protein TAP, and once peptide is acquired, the class I molecule folds and begins its sojourn to the cell surface. To maintain its folded conformation, class I MHC requires peptide but not beta 2m, and the sequence of the peptide bound exercises a subtle influence on the structure of the class I molecule that is likely to be a factor in T cell receptor discrimination of MHC/peptide complexes.

Computer-assisted mapping of infarcted and viable regions of gross cardiac sections following experimental myocardial infarction

We have developed a computer-assisted method that creates digital maps of the viable and infarcted regions of tetrazolium-stained gross cardiac sections. Here we describe and test the method, using a canine occlusion-reperfusion infarction model. Quantitative image analysis showed that the method accurately recorded differences between infarcted and viable regions at a spatial resolution of 5-20 pixels per mm2. Microscopic analysis of tissue samples taken from the sections showed that the maps were accurate. In 15 of 15 cases the histology of the samples matched that predicted by the maps. A comparison of infarct area measurements derived from the maps showed that the method was reproducible. The average intraoperator standard deviation was +/- 8% of a slice's infarcted area and the average interoperator standard deviation was +/- 20%. We conclude that the method creates accurate, detailed, and reproducible maps of the infarcted and viable regions of tetrazolium-stained cardiac sections.

New vectors for manipulation and selection of functional yeast artificial chromosomes (YACs) containing human DNA inserts

A set of fragmentation vectors is described which produce a deletion series of smaller yeast artificial chromosomes (YACs) from a larger parent YAC with the insertion of a eukaryotic selectable marker. In addition, new vectors were designed to permit integration of the genes encoding neomycin (neo) or hygromycin B (hyg) resistance into YACs containing inserts of human DNA. All these vectors are compatible with the yeast host strain AB1380, in which most human genomic YAC libraries are maintained. Linearized vector DNA is used to transform yeast cells in which homologous recombination between human DNA in the YAC and the Alu sequence in the fragmentation or integrating vector produces terminal deletions from the acentromeric (URA3) end of the YAC or insertion of the vector into the YAC, respectively. A set of directional deletions of a YAC is useful for genomic mapping, restriction analysis and functional measurements of large chromosomal regions. The neo and hyg eukaryotic markers permit the study of gene function after introduction of deleted YACs into mammalian cells. Transformation of YACs with the fragmentation vectors resulted in fragmentation in 21-46% of the clones examined; transformation with the integrating vector resulted in integration in 46% of the clones examined.