What do physicians read (and ignore) in electronic progress notes?

OBJECTIVE

Several studies have documented the preference for physicians to attend to the impression and plan section of a clinical document. However, it is not clear how much attention other sections of a document receive. The goal of this study was to identify how physicians distribute their visual attention while reading electronic notes.

METHODS

We used an eye-tracking device to assess the visual attention patterns of ten hospitalists as they read three electronic notes. The assessment included time spent reading specific sections of a note as well as rates of reading. This visual analysis was compared with the content of simulated verbal handoffs for each note and debriefing interviews.

RESULTS

Study participants spent the most time in the "Impression and Plan" section of electronic notes and read this section very slowly. Sections such as the "Medication Profile", "Vital Signs" and "Laboratory Results" received less attention and were read very quickly even if they contained more content than the impression and plan. Only 9% of the content of physicians' verbal handoff was found outside of the "Impression and Plan."

CONCLUSION

Physicians in this study directed very little attention to medication lists, vital signs or laboratory results compared with the impression and plan section of electronic notes. Optimizing the design of electronic notes may include rethinking the amount and format of imported patient data as this data appears to largely be ignored.

In vitro degradation of the inner root sheath in human hair follicles lacking sebaceous glands

BACKGROUND

Cultured hair follicles lacking sebaceous glands do not appear to degrade the inner root sheath (IRS), suggesting that the gland may be involved in this process.

OBJECTIVES

To examine this supposition in cultured hair follicles.

METHODS

Pilosebaceous units were isolated from hair follicles cultured in vitro, and IRS degradation was studied by histology.

RESULTS

When grown in culture, the fibres of follicles lacking sebaceous glands were encased in a layer of translucent tissue. During hair growth in vitro this tissue remained intact at the distal end of the follicle but disappeared further down towards the bulb and then reappeared towards the proximal end. Transection within the region lacking this tissue resulted in the release of a naked hair fibre and the production of hair with no attached tissue upon subsequent hair growth. The translucent tissue represented the IRS, thereby demonstrating that this tissue is indeed degraded in vitro. Histological comparison with freshly isolated pilosebaceous units indicated that IRS degradation in vitro strongly resembled the process that occurs in vivo.

CONCLUSIONS

These data suggest that the sebaceous gland does not itself participate in IRS degradation. Indeed, this phenomenon appears to be a function of the follicle itself and is probably intimately linked with the processes of cellular proliferation, differentiation and death that occur during hair biogenesis.

Electrical stimulation for gastroparesis

BACKGROUND

Gastroparesis is a disabling, and sometimes fatal, disease that often does not respond to medical treatment. This single-surgeon prospective study examines the safety and 6-month efficacy of electrical stimulation for the treatment of gastroparesis.

METHODS

Sixteen patients with medically refractory gastroparesis underwent laparoscopic implantation of an electrical stimulator device (Enterra Therapy, Medtronic, Minneapolis, MN, USA) consisting of a subcutaneous stimulator and two gastric wall leads. Gastric emptying scans (GES) confirmed the diagnosis of gastroparesis. Patients were evaluated preoperatively using a self-administered GI symptomatology questionnaire and RAND 36 Health Survey. Once patients were >6-months from implantation, a repeat GES was obtained and patients completed a postoperative GI symptomatology questionnaire and RAND 36 Health Survey. Ten of 16 patients in this case series were >6-months from implantation. One was lost to follow-up. An F-test was used to establish equality of standard deviations between the 16 patients evaluated preoperatively and the subset of 10 patients evaluated postoperatively. A Student's t-test was used to evaluate the significance of differences in pre- and postoperative results.

RESULTS

Average operating time was 117 min with no intraoperative complications. The majority of patients were discharged on postoperative day 1. There were two complications in the postoperative period. Patients experienced a significant decrease in nausea and vomiting as measured by the GI symptomatology questionnaire. Half of all patients no longer required gastric prokinetic medications and there was a subjective reduction of pyrosis, early satiety, and epigastric pain. A significant increase in quality of life as measured by the RAND 36 Health Survey was seen, and six of eight patients no longer demonstrated gastroparesis on GES.

CONCLUSION

Laparoscopic implantation of an electrical stimulation device is a safe and effective treatment by subjective and objective standards for the management of medically refractory gastroparesis.

Anticipated reactions to genetic testing for hereditary non-polyposis colorectal cancer susceptibility*

Genetic testing for cancer susceptibility (e.g. hereditary non-polyposis colorectal cancer) is available for some families with a history of colon cancer. Our aim was to investigate participants' anticipated emotional and behavioral reactions to genetic testing for colon cancer and whether gender or clinical risk influences these reactions. 437 asymptomatic participants with a colorectal cancer family history completed a questionnaire about anticipated emotions and actions, under different genetic testing scenarios. More women than men anticipated feeling worried, regretful, and angry if tested positive. People at lower-risk anticipated more surprise and disbelief than those at higher-risk. People anticipated feeling more guilt, regret and less relief if they were not tested than if they were. High-risk results were anticipated to increase depression and worry. Most people still wanted screening if at low risk, anticipated leading healthier lifestyles whatever the result, but would make more plans for the future if they were at high risk. Clinical implications are that as anticipated emotional effects of not being tested may be more severe than having a test, people choosing to forgo testing should feel able to reconsider their decision anytime. Most people did not anticipate strong emotional reactions but thought it would change their lifestyle and would like continued clinical surveillance whatever the result.

Lentiviral transduction of green fluorescent protein in retinal epithelium: evidence of rejection

This paper demonstrates lentiviral transduction of the humanized form of the Aequoria victoria gene for green fluorescent protein (GFP) into human fetal retinal pigment epithelium (RPE) in vitro and rabbit RPE in vivo. In vitro GFP expression of cultured human fetal RPE begins within two to three days after 12-16 h of maintained exposure to the virus at titers of 10(8)-10(9) infectious units (IU)/ml. Both stationary and dividing cells are transduced using a lenti viral vector with a cytomegalovirus (CMV) promoter. Expression remains stable for at least three to four months without evidence of toxicity and continues through cell division. In vivo expression is followed non-invasively in rabbit eye using a scanning laser ophthalmoscope (SLO), which can detect single fluorescing retinal cells. In vivo expression begins within a few days after a viral solution is introduced into the subretinal space. A solution of 10(9) IU/ml produces fluorescence within three to four days. Less concentrated solutions lead to slower and less expression. No expression is detectable at concentrations of 10(6) IU/ml. Within one to two weeks after introduction of the viral solution, there is evidence of rejection seen by SLO as a loss of GFP fluorescence and disruption of the RPE. Histology shows damage to the RPE layer and monocytic cell infiltrates in the choroid and subretinal space within the area receiving the viral solution. Strong GFP expression leads to rejection within two weeks. With less expression, rejection is delayed and in some cases undetectable for at least six months. If the GFP gene is not included in the viral vector or if the viral concentration is insufficient to produce detectable GFP expression, rejection is not seen. Using a rhodopsin promoter or injecting the virus intra rather than subretinally produces weak expression and no rejection. Lentivirus can induce expression of a foreign gene in the RPE. Viral induced transduction and GFP expression have no effect on the viability of the RPE in vitro. Continued expression of GFP after cell division implies chromosomal integration of the gene. In vivo expression of GFP in RPE encounters rejection. Rejection may not occur with low GFP expression. The latter occurs with low viral titers, a rhodopsin promoter or intra-retinal injection of viral solution. The results are relevant to gene therapy in retina when gene transduction leads to the expression of foreign proteins.

Vagus nerve stimulation and drug reduction

The authors prospectively assessed drug reduction and patient satisfaction in 21 patients using vagus nerve stimulation (VNS) for refractory epilepsy and compared results to a case-matched control group with a mean follow-up of 13.2 months. Significant antiepileptic drug (AED) reduction occurred in 9/21 (42.9%) of VNS patients averaging 0.43 AED/patient, with dose reduction in four patients (19.0%). For 12/21 (57.1%) patients not reducing AED, dose reduction occurred in 6/21 (28.6%). Drug and dose reduction of AED is possible in patients using VNS for refractory epilepsy without loss of seizure control and with improved patient satisfaction.

A PAK-like protein kinase is required for maturation of young hyphae and septation in the filamentous ascomycete Ashbya gossypii

Filamentous fungi grow by hyphal extension, which is an extreme example of polarized growth. In contrast to yeast species, where polarized growth of the tip of an emerging bud is temporally limited, filamentous fungi exhibit constitutive polarized growth of the hyphal tip. In many fungi, including Ashbya gossypii, polarized growth is reinforced by a process called hyphal maturation. Hyphal maturation refers to the developmental switch from slow-growing hyphae of young mycelium to fast-growing hyphae of mature mycelium. This process is essential for efficient expansion of mycelium. We report for the first time on the identification and characterization of a fungal gene important for hyphal maturation. This novel A. gossypii gene encodes a presumptive PAK (p21-activated kinase)-like kinase. Its closest homolog is the S. cerevisiae Cla4 protein kinase; the A. gossypii protein is therefore called AgCla4p. Agcla4 deletion strains are no longer able to perform the developmental switch from young to mature hyphae, and GFP (green fluorescent protein)-tagged AgCla4p localizes with much higher frequency in mature hyphal tips than in young hyphal tips. Both results support the importance of AgCla4p in hyphal maturation. AgCla4p is also required for septation, indicated by the inability of Agcla4 deletion strains to properly form actin rings and chitin rings. Despite the requirement of AgCla4p for the development of fast-growing hyphae, AgCla4p is not necessary for actin polarization per se, because tips enriched in cortical patches and hyphae with a fully developed network of actin cables can be seen in Agcla4 deletion strains. The possibility that AgCla4p may be involved in regulatory mechanisms that control the dynamics of the actin patches and/or actin cables is discussed.

Rice transposable elements: a survey of 73,000 sequence-tagged-connectors

As part of an international effort to sequence the rice genome, the Clemson University Genomics Institute is developing a sequence-tagged-connector (STC) framework. This framework includes the generation of deep-coverage BAC libraries from O. sativa ssp. japonica c.v. Nipponbare and the sequencing of both ends of the genomic DNA insert of the BAC clones. Here, we report a survey of the transposable elements (TE) in >73,000 STCs. A total of 6848 STCs were found homologous to regions of known TE sequences (E<10(-5)) by FASTX search of STCs against a set of 1358 TE protein sequences obtained from GenBank. Of these TE-containing STCs (TE-STCs), 88% (6027) are related to retroelements and the remaining are transposase homologs. Nearly all DNA transposons known previously in plants were present in the STCs, including maize Ac/Ds, En/Spm, Mutator, and mariner-like elements. In addition, 2746 STCs were found to contain regions homologous to known miniature inverted-repeat transposable elements (MITEs). The distribution of these MITEs in regions near genes was confirmed by EST comparisons to MITE-containing STCs, and our results showed that the association of MITEs with known EST transcripts varies by MITE type. Unlike the biased distribution of retroelements in maize, we found no evidence for the presence of gene islands when we correlated TE-STCs with a physical map of the CUGI BAC library. These analyses of TEs in nearly 50 Mb of rice genomic DNA provide an interesting and informative preview of the rice genome.

The biosynthetic gene cluster for the microtubule-stabilizing agents epothilones A and B from Sorangium cellulosum So ce90

BACKGROUND

Epothilones are produced by the myxobacterium Sorangium cellulosum So ce90, and, like paclitaxel (Taxol((R))), they inhibit microtubule depolymerisation and arrest the cell cycle at the G2-M phase. They are effective against P-glycoprotein-expressing multiple-drug-resistant tumor cell lines and are more water soluble than paclitaxel. The total synthesis of epothilones has been achieved, but has not provided an economically viable alternative to fermentation. We set out to clone, sequence and analyze the gene cluster responsible for the biosynthesis of the epothilones in S. cellulosum So ce90.

RESULTS

A cluster of 22 open reading frames spanning 68,750 base pairs of the S. cellulosum So ce90 genome has been sequenced and found to encode nine modules of a polyketide synthase (PKS), one module of a nonribosomal peptide synthetase (NRPS), a cytochrome P450, and two putative antibiotic transport proteins. Disruptions in the genes encoding the PKS abolished epothilone production. The first PKS module and the NRPS module are proposed to co-operate in forming the thiazole heterocycle of epothilone from an acetate and a cysteine by condensation, cyclodehydration and subsequent dehydrogenation. The remaining eight PKS modules are responsible for the elaboration of the rest of the epothilone carbon skeleton.

CONCLUSIONS

The overall architecture of the gene cluster responsible for epothilone biosynthesis has been determined. The availability of the cluster should facilitate the generation of designer epothilones by combinatorial biosynthesis approaches, and the heterologous expression of epothilones in surrogate microbial hosts.

Intragenic recombination and diversifying selection contribute to the evolution of downy mildew resistance at the RPP8 locus of Arabidopsis

Pathogen resistance (R) genes of the NBS-LRR class (for nucleotide binding site and leucine-rich repeat) are found in many plant species and confer resistance to a diverse spectrum of pathogens. Little is known about the mechanisms that drive NBS-LRR gene evolution in the host-pathogen arms race. We cloned the RPP8 gene (for resistance to Peronospora parasitica) and compared the structure of alleles at this locus in resistant Landsberg erecta (Ler-0) and susceptible Columbia (Col-0) accessions. RPP8-Ler encodes an NBS-LRR protein with a putative N-terminal leucine zipper and is more closely related to previously cloned R genes that confer resistance to bacterial pathogens than it is to other known RPP genes. The RPP8 haplotype in Ler-0 contains the functional RPP8-Ler gene and a nonfunctional homolog, RPH8A. In contrast, the rpp8 locus in Col-0 contains a single chimeric gene, which was likely derived from unequal crossing over between RPP8-Ler and RPH8A ancestors within a Ler-like haplotype. Sequence divergence among RPP8 family members has been accelerated by positive selection on the putative ligand binding region in the LRRs. These observations indicate that NBS-LRR molecular evolution is driven by the same mechanisms that promote rapid sequence diversification among other genes involved in non-self-recognition.

Intragenic recombination and diversifying selection contribute to the evolution of downy mildew resistance at the RPP8 locus of Arabidopsis

Pathogen resistance (R) genes of the NBS-LRR class (for nucleotide binding site and leucine-rich repeat) are found in many plant species and confer resistance to a diverse spectrum of pathogens. Little is known about the mechanisms that drive NBS-LRR gene evolution in the host-pathogen arms race. We cloned the RPP8 gene (for resistance to Peronospora parasitica) and compared the structure of alleles at this locus in resistant Landsberg erecta (Ler-0) and susceptible Columbia (Col-0) accessions. RPP8-Ler encodes an NBS-LRR protein with a putative N-terminal leucine zipper and is more closely related to previously cloned R genes that confer resistance to bacterial pathogens than it is to other known RPP genes. The RPP8 haplotype in Ler-0 contains the functional RPP8-Ler gene and a nonfunctional homolog, RPH8A. In contrast, the rpp8 locus in Col-0 contains a single chimeric gene, which was likely derived from unequal crossing over between RPP8-Ler and RPH8A ancestors within a Ler-like haplotype. Sequence divergence among RPP8 family members has been accelerated by positive selection on the putative ligand binding region in the LRRs. These observations indicate that NBS-LRR molecular evolution is driven by the same mechanisms that promote rapid sequence diversification among other genes involved in non-self-recognition.

Activation of latent transgenes in Arabidopsis using a hybrid transcription factor

A hybrid transcription factor comprising a fusion of the DNA-binding domain of Saccharomyces cerevisiae GAL4 and the transcription activation domain of maize C1 was expressed in stably transformed Arabidopsis. Additional transgenic lines were created containing test genes controlled by a synthetic promoter consisting of concatemeric copies of the cis-acting site recognized by GAL4 (UASG) fused to a minimal promoter. The GAL4/C1 effector line was crossed to two lines containing a synthetic promoter/GUS fusion. Both histochemical staining and GUS activity assays indicate strong activation of GUS expression was achieved only after crossing. The GAL4/C1 effector line was also crossed to 15 lines containing a synthetic promoter/antisense adenylosuccinate synthetase gene. Severely retarded growth, and in some cases lethality, was observed in 40% of the F1 lines. This system of activation by crossing is generally useful for activating expression of test transgenes.

Cloning and sequence analysis of the putative rifamycin polyketide synthase gene cluster from Amycolatopsis mediterranei

The 54-kbp Type I polyketide synthase gene cluster, most probably involved in rifamycin biosynthesis by Amycolatopsis mediterranei, was cloned in E. coli and completely sequenced. The DNA encodes five closely packed, very large open reading frames reading in one direction. As expected from the chemical structure of rifamycins, ten polyketide synthase modules and a CoA ligase domain were identified in the five open reading frames which contain one to three polyketide synthase modules each. The order of the functional domains on the DNA probably reflects the order in which they are used because each of the modules contains the predicted acetate or propionate transferase, dehydratase, and beta-ketoacyl-ACP reductase functions, required for the respective step in rifamycin biosynthesis.

Molecular and cellular characterization of baboon C-Raf as a target for antiproliferative effects of antisense oligonucleotides

C-Raf is a an essential member of the growth factor-ras pathway and a target for intervention strategies aimed at blocking cell proliferative responses. Excessive smooth muscle proliferation is considered one cause of the arterial closure in restenosis. Because of the similarity to the human cardiovascular system, a useful current animal model of the disease is a baboon model. As a foundation for animal studies employing antisense oligonucleotides, efforts were made to characterize the molecular and cellular biology of the baboon system. The nucleotide sequence of baboon c-raf cDNA was determined. Antisense phosphorothioate oligonucleotides specific to the 3'-UTR of c-raf mRNA from human and baboon were compared using primary baboon smooth muscle cells in culture. A particular human antisense oligonucleotide, referred to as ISIS 5132, was different by only 2 of 20 bases from the baboon sequence. The corresponding baboon antisense oligonucleotide ISIS 12959, however, was markedly more effective to inhibit c-raf mRNA, protein production, and DNA synthesis, and the results attest to the species specificity of the approach. After antisense treatment, c-raf mRNA levels dropped rapidly, whereas protein levels decreased with a half-life of roughly 24-48 hours, consistent with the antiproliferative effects. The data are discussed with regard to the profile of protein-protein interactions made by C-Raf and with the view that the baboon system closely parallels the human one at the signal transduction level. As this work progressed, a baboon cDNA homolog of a human c-raf-2 pseudogene was isolated, sequenced, and shown to be transcribed into mRNA.

Sequences in the human immunodeficiency virus type 1 U3 region required for in vivo and in vitro integration

A series of mutants with alterations in the U3 region of the human immunodeficiency virus type 1 long terminal repeat were made, and the effects of these mutations were evaluated both in vitro and in vivo. When the subterminal 6 to 8 nucleotides of the U3 long terminal repeat were mutated, the resulting provirus was unable to efficiently replicate in vivo, and a mutant oligonucleotide which mimicked the mutation could not be efficiently cleaved but could be joined to target DNA by wild-type recombinant integrase protein in vitro. These results suggest that this region is important in the specific recognition of the viral DNA by the integrase protein.

Transfer and expression of the human multiple drug resistance gene in human CD34+ cells

The human multiple-drug resistance (MDR1) gene has been transferred into human hematopoietic progenitors using retroviral gene transfer. Human bone marrow cells and isolated CD34+ cells isolated from marrow were exposed to growth factors interleukin-3 (IL-3), IL-6, and stem cell factor for 48 hours and then to two changes of MDR retroviral supernatants over the next 24 hours. Progenitor assays in methylcellulose at this time showed that 18% to 70% of BFU-E and 30% to 60% of CFU-GM contain the transferred MDR gene by polymerase chain reaction analysis. Up to 11.2% of the progeny of these cells express increased amounts of MDR glycoprotein on their surface by fluorescence-activated cell sorter (FACS) analysis. In addition, transduced cells are enriched in high MDR-expressing cells after exposure to taxol as assessed by FACS analysis, and by resistance of BFU-E to taxol (Bristol-Myers Squibb, Princeton, NJ). These studies indicate the feasibility of using MDR gene transfer as a means of enriching marrow for MDR-transduced cells. They also provide the basis of a phase 1 clinical protocol in patients with advanced cancers not involving the bone marrow for the use of MDR gene transfer as a means of protecting marrow cells, which normally express low levels of MDR, from the myelosuppressive effects of drugs like taxol.

Human immunodeficiency virus type 1 mutants resistant to nonnucleoside inhibitors of reverse transcriptase arise in tissue culture

We have recently described a nonnucleoside compound that specifically inhibits the reverse transcriptase of human immunodeficiency virus type 1 (HIV-1), the causative agent of AIDS. This compound, nevirapine (BI-RG-587), interacts with highly conserved tyrosine residues at positions 181 and 188 in the reverse transcriptase to inhibit the recombinant enzyme and virus replication in cell culture with 50% inhibitory concentrations in the 40 nM range. HIV-1 variants resistant to nevirapine emerged with passage in cell culture in the presence of drug. This resistant phenotype was stable with continued passage in the absence of drug. These mutants had a substitution of cysteine for the tyrosine at position 181. Introduction of this mutation into the recombinant enzyme increased the inhibitory concentration of nevirapine 100-fold. Substitution of cysteine for tyrosine at residue 181 into the wild-type viral genome conferred a similar reduction in susceptibility to nevirapine. Mutants were also resistant to a tetrahydroimidazo[4,5,1-jk][1,4]benzodiazepin-2(1H)-one and -thione derivative and two 6-phenylthiouracil derivatives but retained their sensitivity to the other reverse transcriptase inhibitors, 3'-azido-3'-deoxythymidine and foscarnet.

Retroviral gene transfer using safe and efficient packaging cell lines

One of the requirements for the use of retroviral vectors in human gene therapy is a packaging cell line which is incapable of producing replication-competent virus and which produces high titers of replication-deficient vector virus. Wild-type virus may be produced through recombinational events between the helper virus and a retroviral vector. We have constructed an ecotropic packaging cell line, GP + E-86, and an amphotropic packaging cell line, GP + envAm12, in which the viral gag and pol genes are on one plasmid and the viral env gene is on another plasmid. Both plasmids contain deletions of the packaging sequence and the 3' LTR. The fragmented helper virus genomes, when introduced into 3T3 cells, produce titers of retrovirus which are comparable to the titers produced from packaging cells containing the helper virus genome on a single plasmid. We have found no evidence for the generation of wild-type retrovirus using the GP + E-86 and GP + envAm12 packaging lines, either alone or in combination with the N2 retroviral vector. We also show that these packaging cell lines can be used to transfer the neoR gene of the N2 vector into mouse hematopoietic cells, followed by successful (48-52%), long-term (up to 200 days) transplantation into irradiated recipients. These results indicate that these packaging lines are safe and efficient for use in experiments designed for murine (using GP + E-86) and human (using GP + envAm12) gene therapy.

Construction and use of a safe and efficient amphotropic packaging cell line

An amphotropic retrovirus packaging cell line was constructed in which the gag, pol, and env genes of the helper virus are separated on two different plasmids and in which the packaging signals and 3' long terminal repeats are removed. To do this, a plasmid containing the Moloney murine leukemia virus gag and pol gene was transfected into NIH 3T3 cells, and a plasmid containing the 4070A amphotropic env gene was transfected into one of the resulting clones which produced a high level of reverse transcriptase. A clone producing a high level of amphotropic env protein (GP + envAm12) was then isolated. When transfected into GP + envAm12 cells, titers of the retroviral vector N2, containing a neomycin resistance gene, ranged from 10(2) to greater than 10(6) CFU/ml on 3T3 cells, from 1.3 x 10(4) to 2.7 x 10(5) CFU/ml on HeLa cells, and from 1.0 x 10(2) to 6.0 x 10(3) CFU/ml on K562 cells when assayed by G418 resistance. These titers were comparable to titers obtained using the PA317 cell line. Tests for the safety of the GP + envAm12 packaging line showed no evidence for the generation of wild-type virus. Thus, the efficiency and safety of the GP + envAm12 cell line in gene transfer into human cells may provide an optimal system for experiments whose goal is human gene therapy.

A safe packaging line for gene transfer: separating viral genes on two different plasmids

A retrovirus packaging cell line was constructed by using portions of the Moloney murine leukemia virus in which the gag, pol, and env genes of the helper virus were separated onto two different plasmids and in which the psi packaging signal and 3' long terminal repeat were removed. The plasmid containing the gag and pol genes and the plasmid containing the env gene were cotransfected into NIH 3T3 cells. Clones that produced high levels of reverse transcriptase and env protein were tested for their ability to package the replication-defective retrovirus vectors delta neo and N2. One of the gag-pol and env clones (GP+E-86) was able to transfer G418 resistance to recipient cells at a titer of as high as 1.7 X 10(5) when it was used to package delta neo and as high as 4 X 10(6) when it was used to package N2. Supernatants of clones transfected with the intact parent gag-pol-env plasmid 3P0 had comparable titers (as high as 6.5 X 10(4) with delta neo; as high as 1.7 X 10(5) with N2). Tests for recombination events that might result in intact retrovirus showed no evidence for the generation of replication-competent virus. These results suggest that gag, pol, and env, when present on different plasmids, may provide an efficient and safe packaging line for use in retroviral gene transfer.

Construction of a safe and efficient retrovirus packaging cell line

Ecotropic and amphotropic retrovirus packaging cell lines have been constructed in which the helper virus genome have been separated onto two plasmids, and the psi packaging signal and 3' LTR have been removed. The gag and pol genes on one plasmid and the env gene on another plasmid were transfected into NIH 3T3 cells. Packaging cell lines produced by these transfected genes released titers of replication-defective retroviral vectors which were comparable to titers produced by packaging cell lines containing the helper virus genome on one plasmid. There has been no evidence of recombination events between the ecotropic helper virus plasmids and the vector virus plasmid that would result in the generation of intact replication-competent virus. These results suggest that a packaging cell line containing gag, pol and env on different plasmids is efficient and safe for use in retroviral gene gransfer.

Human beta-globin gene expression after gene transfer using retroviral vectors

A retroviral vector containing a 4.4-kb Pst I human beta S-globin gene and a neomycin resistance gene was used to infect NIH-3T3 and mouse erythroleukemia cells (MELC). In MELC, human beta-globin mRNA transcripts are transcribed and properly initiated and spliced. In some cases, there is an appropriate increase in beta-globin mRNA on addition of dimethylsulfoxide (DMSO), an inducer of hemoglobin synthesis and erythroid differentiation in these cells. When NIH-3T3 cells are infected with the same retroviral vector, there is less globin mRNA accumulation and no evidence for appropriate regulation. Human beta-globin gene expression in MELC clones induced with DMSO is 2-3% that of endogenous mouse beta-globin gene expression. These results indicate that retroviral vectors can be used to transfer and appropriately express human beta-globin genes in erythroid cells.

Epiploic appendicitis: CT characteristics

Acute infarction of an appendix epiploica resulted in an inflammatory process involving the caudal aspect of the transverse colon and the adjacent greater omentum. Computed tomography demonstrated prominent linear soft tissue densities, an increase in CT number of the involved greater omentum, and posterior displacement of the small bowel. In the setting of acute abdominal pain the location and focal nature of the inflammatory process as seen on CT may allow the radiologist to suggest the correct diagnosis.

The mouse c-abl locus: molecular cloning and characterization

The mouse c-abl gene, part of the sequence of which was captured in Moloney murine leukemia virus to generate the transforming gene (v-abl) of the Abelson murine leukemia virus, has been isolated and characterized. The c-abl locus spans 40 kb in the mouse genome with the v-abl homologies distributed in no less than ten clusters along 25 kb of the cloned DNA. Partial sequence of the v-abl homologous regions indicates that v-abl derived from c-abl mainly by splicing of multiple exons of the c-abl gene. The c-abl sequences can be subdivided into two regions: a tyrosine kinase coding sequence distributed among eight small clusters on the 5' end of the gene and a C-terminal portion consisting of one small and one large cluster, which are needed neither for the tyrosine kinase activity nor for the transforming ability of v-abl. Apparent exon/intron boundaries in the homologous kinase-coding regions of c-abl and c-src are at different locations.

Isolation and properties of Moloney murine leukemia virus mutants: use of a rapid assay for release of virion reverse transcriptase

A rapid assay for retroviral reverse transcriptase activity released into the culture medium by infected cells was developed. With the assay, 4,000 clonally infected cell lines could be tested in a few hours. We have adapted the assay for use as a screen for the detection of spontaneous viral mutants. Mutants of Moloney murine leukemia virus have been isolated which (i) produce a thermolabile reverse transcriptase, (ii) are temperature sensitive for release of enzyme activity, or (iii) can only productively infect cells already producing gag-related polypeptides. The assay has also been useful for the isolation of nonproducer cells infected with various replication-defective transforming viruses.

A transformation-defective mutant of Abelson murine leukemia virus lacks protein kinase activity

A transformation-defective mutant of Abelson murine leukemia virus (A-MuLV), called A-MuLV-P92td, has been isolated. The mutant encodes a serologically identifiable A-MuLV protein of molecular weight 92,000 (P92) but it lacks the ability to transform either fibroblasts or bone marrow lymphoid cells. In contrast to the protein made by transforming strains of A-MuLV, the protein made by A-MuLV-P92td does not becme phosphorylated during in vitro incubation with [gamma-32P]ATP. If the protein is mixed with proteins from cells transformed by a functional A-MuLV strain, phosphorylation of P92 occurs, showing that its ability to accept phosphate is not altered by the mutation. These parallel changes provide genetic evidence that the A-MuLV protein is a transforming protein and that its associated protein kinase activity (EC 2.7.1.37) is a crucial part of its transforming ability.

Structure of a cloned circular Moloney murine leukemia virus DNA molecule containing an inverted segment: implications for retrovirus integration

Closed circular Moloney murine leukemia virus (M-MuLV) DNA was prepared from recently infected cells and cloned in a lambda vector. Four classes of cloned M-MuLV inserts were found: Class I, full length 8.8-kilobase (kb) inserts with two tandem long terminal repeats (LTRs) of 600 base pairs; class 2, 8.2-kb inserts with a single copy of a LTR; class 3, M-MuLV DNA inserts with various portions deleted; and class 4, an 8.8-kb insert with an internal sequence inversion. Determination of nucleotide sequence at the junction between the two LTRs from a class 1 insert suggested that circularization occurred by blunt-end ligation of an 8.8-kb linear DNA. The class 4 molecule had an inversion that was flanked by inverted LTRs, each of which had lost two terminal base pairs at the inversion end points. Also, four base pairs that were present only once in standard M-MuLV DNA were duplicated at either end of the inversion. This molecule was interpreted as resulting from an integrative inversion in which M-MuLV DNA has integrated into itself. Its analysis thus provided explicit information concerning the mechanism by which retrovirus DNA integrates into host cell DNA. Models of retrovirus integration based on bacterial DNA transposition mechanisms are proposed.

Structure of the Abelson murine leukemia virus genome

Virions produced from cells transformed by A-MuLV contain a 30S, 5.6 kb RNA that can be translated in a cell-free system to form the characteristic A-MuLV protein. This RNA was mapped by heteroduplex methods using DNA probes from M-MuLV, the presumed parent of A-MuLV. The overall organization of the RNA was determined by using full-length M-MuLV reverse transcribed DNA and visualizing the heteroduplexes in the electron microscope. This showed that A-MuLV and M-MuLV have homologous sequences at both ends of their RNAs but that the central portion of the A-MuLV genome is not homologous to sequences in M-MuLV RNA. A precise measure of the lengths of the shared regions was obtained by using S1 nuclease to digest hybrids between 32P-labeled M-MuLV DNA and A-MuLV RNA; the resulting fragments were analyzed for their length by electrophoresis. The regions of homology were shown to be 1320 nucleotides long at the 5' end and 730 nucleotides long at the 3' end. Thus approximately 6200 nucleotides of the approximately 8300 in M-MuLV RNA were deleted when the A-MuLV genome was formed, but an insert of 3600 nucleotides, presumably derived from the normal murine genome, was inserted in place of the deleted region.

Synthesis of a 600-nucleotide-long plus-strand DNA by virions of Moloney murine leukemia virus

A discrete, 600-nucleotide-long plus-strand DNA has been identified among the products of reverse transcription by virions of Moloney murine leukemia virus. Its polarity was shown by hybridization to minus-strand DNA. It appears to be copied from the right end of minus-strand DNA because (i) its restriction endonuclease cleavage pattern corresponds to the redundant 600-base segment found at either end of the ultimate double-stranded reverse transcription products, (ii) its synthesis is actinomycin D sensitive, and (iii) its synthesis begins during the first hour of a reverse transcription reaction when only the right-hand end of minus-strand DNA is available as template. We therefore call this DNA plus-strong-stop DNA by analogy with the minus-strong-stop DNA copied from the left end of the viral RNA. Both strong-stop DNAs are made early during in vitro reactions and decline in concentration later, consistent with postulated roles as initiators of long minus- and plus-strand DNA. Unlike minus-strong-stop DNA, plus-strong-stop DNA remains as a double-stranded nucleic acid after its synthesis, as shown by S1 nuclease resistance. A primer to initiate plus-strong-stop DNA synthesis has not been identified; the product found thus far has no detectable RNA attached to it.

A detailed model of reverse transcription and tests of crucial aspects

A model of reverse transcription has been devised by which the detailed architecture of ten molecular structures is predicted. The model includes a number of novel features for which experimental evidence is presented. First, growing minus DNA strand is copied from the viral RNA only up to a position about 150 nucleotides from the 5' end of the RNA. Second, plus-strand DNA, after being copied from approximately 600 nucleotides at the 5' end of the minus-strand DNA, then transcribes the first approximately 20 nucleotides of the tRNApro primer (which is covalently attaced to the 5' end of the minus DNA strand). The 3' ends of the minus and plus DNA probably form a hybrid through the homology conferred by the primer binding site sequences. Third, the minus and plus DNA strands are elongated in a continuous fashion resulting in a linear double-stranded DNA molecule containing a 600 nucleotide direct repeat at both ends. The most of the features of the model have experimental support, and it appears to provide a credible description of reverse transcription.

In vitro synthesis of a 9 kbp terminally redundant DNA carrying the infectivity of Moloney murine leukemia virus

Detergent-disrupted virions of Moloney murine leukemia virus synthesize a 9 kbp double-stranded infectious DNA. It contains mainly full-length, single-stranded DNA, and its infectivity and size are insensitive to digestion by the single-strand-specific S1 nuclease. Analysis of fragmentation of the DNA using restriction endonucleases has shown that it is indistinguishable from the linear double-stranded DNA synthesized in infected cells. On the basis of the positions of the cleavage sites for a number of enzymes, the 9 kbp DNA has a 575 base direct terminal repetition. It is longer than the viral RNA at both ends, evidently due to repetitive copying of segments of the RNA. Virions also synthesize an 8.4 kbp double-stranded circular DNA that lacks one copy of the terminal repetition, as well as viral DNA longer than 9 kbp. The enzymatic machinery in the virions of retroviruses therefore appears to be responsible for all the steps involved in making fully double-stranded linear and one form of circular DNA.