Spontaneous Phenotypes Research Articles

Abstract 117: Transplantation of Bone Marrow Cells from miR-150-KO Mice Improves Immune Function and Attenuates Arterial Stiffness and Hypertension in Senescence-Accelerated Mice

Background and Objective: Aging is associated with increased prevalence of arterial stiffness and hypertension. The senescence-accelerated mouse (SAMP1) demonstrates early and spontaneous aging phenotypes around 6-8 months of age. In contrast, microRNA-150 knockout (miR-150 KO) slows down the aging process and extends lifespan in mice by 20-30%. The object of this study is to investigate whether transplantation of bone marrow cells (BMCs) from miR-150 KO mice attenuates arterial stiffening and hypertension in SAMP1 mice. Method and Results: Pulse wave velocity (PWV) and blood pressure (BP) levels were increased significantly in the SAMP1 mice compared with the age-matched control (AKR/J) mice (10 months), indicating that SAMP1 mice developed arterial stiffening and hypertension. Interestingly, transplantation of bone marrow cells (BMCs) from miR-150-KO mice decreased PWV and BP in SAMP1 mice to nearly control levels within 3 months. BMC transplantation decreased expression of collagen1, TGFβ1, Scleraxis (collagen gene transcription factor), MMP-2 and MMP-9 but increased expression of elastin in aortas of SAMP1 mice, indicating improved arterial remodeling. BMC transplantation from miR-150-KO mice partially rescued the downregulation of B cells lymphocytes and increased the serum level of IgG and IgM, abolished infiltration of T cells and macrophages, and decreased inflammatory cytokine expression in aortas in SAMP1 mice. In the cell culture study, IgG deficiency increased inflammatory factor cytokine expression in endothelial cells, which can be abolished by addition of IgG protein. Conclusion: BMC transplantation from miR-150-KO mice reversed arterial stiffness and hypertension in SAMP1 mice likely via modulation of the immune function. This study demonstrates, for the first time, that BMC transplantation may be an effective therapeutic strategy for aging-related arterial stiffness and hypertension.

Immune Relevant and Immune Deficient Mice: Options and Opportunities in Translational Research.

In 1989 ILAR published a list and description of immunodeficient rodents used in research. Since then, advances in understanding of molecular mechanisms; recognition of genetic, epigenetic microbial, and other influences on immunity; and capabilities in manipulating genomes and microbiomes have increased options and opportunities for selecting mice and designing studies to answer important mechanistic and therapeutic questions. Despite numerous scientific breakthroughs that have benefitted from research in mice, there is debate about the relevance and predictive or translational value of research in mice. Reproducibility of results obtained from mice and other research models also is a well-publicized concern. This review summarizes resources to inform the selection and use of immune relevant mouse strains and stocks, aiming to improve the utility, validity, and reproducibility of research in mice. Immune sufficient genetic variations, immune relevant spontaneous mutations, immunodeficient and autoimmune phenotypes, and selected induced conditions are emphasized.

Mitochondrial polymorphisms contribute to aging phenotypes in MNX mouse models.

Many inbred strains of mice develop spontaneous tumors as they age. Recent awareness of the impacts of mitochondrial DNA (mtDNA) on cancer and aging has inspired developing a mitochondrial-nuclear exchange (MNX) mouse model in which nuclear DNA is paired with mitochondrial genomes from other strains of mouse. MNX mice exhibit mtDNA influences on tumorigenicity and metastasis upon mating with transgenic mice. However, we also wanted to investigate spontaneous tumor phenotypes as MNX mice age. Utilizing FVB/NJ, C57BL/6J, C3H/HeN, and BALB/cJ wild-type inbred strains, previously documented phenotypes were observed as expected in MNX mice with the same nuclear background. However, aging nuclear matched MNX mice exhibited decreased occurrence of mammary tumors in C3H/HeN mice containing C57BL/6J mitochondria compared to wild-type C3H/HeN mice. Although aging tumor phenotypes appear to be driven by nuclear genes, evidence suggesting that some differences are modified by the mitochondrial genome is presented.

Foxp3-driven miR-23~27~24 clusters control regulatory T cell-mediated immune regulation

Abstract CD4+ Foxp3+ regulatory T (Treg) cells maintain immune homeostasis by regulating pathologic immune responses against self-, innocuous as well as dangerous foreign antigens. Previously, microRNA (miRNA)-mediated gene regulation has been shown to play a pivotal role in the maintenance and function of Treg cells. Here, we report that miR-23~27~24 clusters, which are abundantly expressed in Treg cells, are critical in controlling Treg cell biology. Foxp3 directly promotes elevated expressions of miR-23~27~24 clusters required for optimal Treg cell function through binding to the “enhancer element” at the miR-23~27~24 loci. Loss of miR-23~27~24 clusters in Treg cells lead to the development of spontaneous lympho-hyperactivation phenotypes over time. Moreover, upon allergen challenge, mice with Treg cell-specific ablation of miR-23~27~24 clusters exhibited elevated eosinophilic airway inflammation. Together, our results identify a Foxp3-driven miRNA family that plays important roles in controlling Treg cell-mediated immune regulation at both physiological and pathological settings.

Abstract 16694: Transplantation of Bone Marrow Cells From miR150 Knockout Mice Attenuates Arterial Stiffness and Hypertension in Senescence-accelerated Mice P1 (SAMP1)

Background & Objective. Aging is associated with increased prevalence of arterial stiffness and hypertension. The senescence-accelerated mouse P1 (SAMP1) demonstrates early and spontaneous aging phenotypes around 6-8 months of age. In contrast, microRNA-150 knockout (miR15-KO) slows down the aging process and extends lifespan in mice by 20-30%. The objective of this study is to investigate if arterial stiffness and hypertension occur in SAMP1 mice and if transplantation of bone marrow cells (BMCs) from miR-150 KO mice affects arterial stiffening and hypertension in SAMP1 mice. Method & Results. The results showed that blood pressure (BP) and pulse wave velocity (PWV) were increased significantly in the SAMP1 mice vs. the age-matched control (AKR/J) mice (10 months). Therefore, SAMP1 mice developed arterial stiffening and hypertension. Western blot analysis showed that collagen 1 and TGFβ1 expression were increased but the elastin expression was decreased in aortas of SAMP1 mice, indicating arterial remodeling. Klotho is a recently-discovered aging-suppressor gene. Plasma levels klotho protein and renal expression of klotho protein were decreased in SAMP1 mice. Interestingly, transplantation of BMCs from miR150-KO mice decreased PWV and BP in SAMP1 mice to nearly control levels within 3 months, suggesting that BMC transplantation attenuates senescence-related arterial stiffening and hypertension. BMC transplantation from miR150-KO mice increased plasma levels of klotho and renal expression of klotho and abolished T cell and macrophage infiltration in aortas and kidneys in SAMP1 mice. BMC transplantation decreased expression of collagen 1 and TGFβ1 but increased expression of elastin in aortas in SAMP1 mice. Conclusion. Accelerated aging led to arterial stiffness and hypertension in SAMP1 mice. BMC transplantation from miR150-KO mice reversed arterial stiffness and hypertension in SAMP1 mice. This study demonstrates, for the first time, that BMC transplantation may be an effective therapeutic approach for aging-related arterial stiffness and hypertension. (supported by NIH R01 HL105302 & HL102074).

Quantification of larval zebrafish motor function in multiwell plates using open-source MATLAB applications.

This article describes a method to quantify the movements of larval zebrafish in multiwell plates, using the open-source MATLAB applications LSRtrack and LSRanalyze. The protocol comprises four stages: generation of high-quality, flatly illuminated video recordings with exposure settings that facilitate object recognition; analysis of the resulting recordings using tools provided in LSRtrack to optimize tracking accuracy and motion detection; analysis of tracking data using LSRanalyze or custom MATLAB scripts; and implementation of validation controls. The method is reliable, automated and flexible, requires <1 h of hands-on work for completion once optimized and shows excellent signal:noise characteristics. The resulting data can be analyzed to determine the following: positional preference; displacement, velocity and acceleration; and duration and frequency of movement events and rest periods. This approach is widely applicable to the analysis of spontaneous or stimulus-evoked zebrafish larval neurobehavioral phenotypes resulting from a broad array of genetic and environmental manipulations, in a multiwell plate format suitable for high-throughput applications.

A Novel Intergenic ETnII-β Insertion Mutation Causes Multiple Malformations in Polypodia Mice

Mouse early transposon insertions are responsible for ∼10% of spontaneous mutant phenotypes. We previously reported the phenotypes and genetic mapping of Polypodia, (Ppd), a spontaneous, X-linked dominant mutation with profound effects on body plan morphogenesis. Our new data shows that mutant mice are not born in expected Mendelian ratios secondary to loss after E9.5. In addition, we refined the Ppd genetic interval and discovered a novel ETnII-β early transposon insertion between the genes for Dusp9 and Pnck. The ETn inserted 1.6 kb downstream and antisense to Dusp9 and does not disrupt polyadenylation or splicing of either gene. Knock-in mice engineered to carry the ETn display Ppd characteristic ectopic caudal limb phenotypes, showing that the ETn insertion is the Ppd molecular lesion. Early transposons are actively expressed in the early blastocyst. To explore the consequences of the ETn on the genomic landscape at an early stage of development, we compared interval gene expression between wild-type and mutant ES cells. Mutant ES cell expression analysis revealed marked upregulation of Dusp9 mRNA and protein expression. Evaluation of the 5′ LTR CpG methylation state in adult mice revealed no correlation with the occurrence or severity of Ppd phenotypes at birth. Thus, the broad range of phenotypes observed in this mutant is secondary to a novel intergenic ETn insertion whose effects include dysregulation of nearby interval gene expression at early stages of development.

Risk‐induced hatching timing shows low heritability and evolves independently of spontaneous hatching in red‐eyed treefrogs

Plasticity in the timing of transitions between stages of complex life cycles allows organisms to adjust their growth and development to local environmental conditions. Genetic variation in such plasticity is common, but the evolution of context-dependent transition timing may be constrained by information reliability, lag-time and developmental constraints. We studied the genetic architecture of hatching plasticity in embryos of the red-eyed treefrog (Agalychnis callidryas) in response to simulated predator attacks using a series of paternal and maternal half-sibs from a captive breeding colony of wild-collected animals. We compared the developmental timing of induced early hatching across sibships and estimated cross-environment genetic correlations between induced and spontaneous hatching traits. Additive genetic variance for induced early hatching was very low, indicating a constraint on the short-term evolution of earlier hatching timing. This constraint is likely related to the maturation of the hatching mechanism. The most plastic genotypes produced the most extreme spontaneous hatching phenotypes, indicating that developmental range, per se, is not constrained. Cross-environment genetic correlation in hatching timing was negligible, so the evolution of spontaneous hatching in this species has not depended on the evolution of risk-induced hatching and vice versa.

Isolation and characterization of a Laccase gene potentially involved in proanthocyanidin polymerization in oriental persimmon (Diospyros kaki Thunb.) fruit

Proanthocyanidins (PAs, condensed tannins) are important health-promoting phytochemicals that are abundant in many plants. Oriental persimmon (Diospyros kaki Thunb.) is an excellent source of PAs because of its unique ability to accumulate large quantities of these compounds in its young fruit. There are two different spontaneous mutant phenotypes of oriental persimmons which lose their astringent taste naturally on the tree; while plants without these mutations remain rich in soluble PAs until the fruit fully ripened. The mutations are referred to as pollination-constant non-astringent genotypes named J-PCNA and C-PCNA, and are from Japan and China respectively. In this work we speculated that the loss of astringency in C-PCNA fruit is due to the soluble PAs transferred into insoluble upon polymerization, which was quite different from that of the J-PCNA. A DkLAC1 gene was isolated by the homology-based clone method. The predicted protein product of this gene showed that the DkLAC1 is a plant laccase which is phylogenetically related to the known enzyme AtLAC15 involved in the polymerization of PAs. Expression patterns of PAs biosynthetic genes associated with soluble PAs contents in three types of Oriental persimmons. Expression levels of DkLAC1 in C-PCNA type plants were linked with the reduction of soluble PAs in the flesh of the fruit. In addition the cis-elements in the DkLAC1 promoter regions indicated that the gene might also be regulated by the DkMYB4 as is seen with other well-known structural genes in Oriental persimmon. We conclude that DkLAC1 is potentially involved in PA polymerization in C-PCNA during normal ripening in C-PCNA persimmon.

A Nine Amino Acid Domain Is Essential for Mutant Prion Protein Toxicity

Transgenic mice expressing prion protein (PrP) molecules with several different internal deletions display spontaneous neurodegenerative phenotypes that can be dose-dependently suppressed by coexpression of wild-type PrP. Each of these deletions, including the largest one (Δ32-134), retains 9 aa immediately following the signal peptide cleavage site (residues 23-31; KKRPKPGGW). These residues have been implicated in several biological functions of PrP, including endocytic trafficking and binding of glycosaminoglycans. We report here on our experiments to test the role of this domain in the toxicity of deleted forms of PrP. We find that transgenic mice expressing Δ23-134 PrP display no clinical symptoms or neuropathology, in contrast to mice expressing Δ32-134 PrP, suggesting that residues 23-31 are essential for the toxic phenotype. Using a newly developed cell culture assay, we narrow the essential region to amino acids 23-26, and we show that mutant PrP toxicity is not related to the role of the N-terminal residues in endocytosis or binding to endogenous glycosaminoglycans. However, we find that mutant PrP toxicity is potently inhibited by application of exogenous glycosaminoglycans, suggesting that the latter molecules block an essential interaction between the N terminus of PrP and a membrane-associated target site. Our results demonstrate that a short segment containing positively charged amino acids at the N terminus of PrP plays an essential role in mediating PrP-related neurotoxicity. This finding identifies a protein domain that may serve as a drug target for amelioration of prion neurotoxicity.

Arabidopsis metacaspase 2d is a positive mediator of cell death induced during biotic and abiotic stresses

Cysteine proteases such as caspases play important roles in programmed cell death (PCD) of metazoans. Plant metacaspases (MCPs), a family of cysteine proteases structurally related to caspases, have been hypothesized to be ancestors of metazoan caspases, despite their different substrate specificity. Arabidopsis thaliana contains six type II MCP genes (AtMCP2a-f). Whether and how these individual members are involved in controlling PCD in plants remains largely unknown. Here we investigated the function and regulation of AtMCP2d, the predominant and constitutively expressed member of type II MCPs, in stress-inducible PCD. Two AtMCP2d mutants (mcp2d-1 and mcp2d-3) exhibited reduced sensitivity to PCD-inducing mycotoxin fumonisin B1 as well as oxidative stress inducers, whereas AtMCP2d over-expressors were more sensitive to these agents, and exhibited accelerated cell-death progression. We found that AtMCP2d exclusively localizes to the cytosol, and its accumulation and self-processing patterns were age-dependent in leaves. Importantly, active proteolytic processing of AtMCP2d proteins dependent on its catalytic activity was observed in mature leaves during mycotoxin-induced cell death. We also found that mcp2d-1 leaves exhibited reduced cell death in response to Pseudomonas syringae carrying avirulent gene avrRpt2, and that self-processing of AtMCP2d was also detected in wild-type leaves in response to this pathogen. Furthermore, increases in processed AtMCP2d proteins were found to correlate with conditional cell-death induction in two lesion-mimic mutants (cpr22 and ssi4) that exhibit spontaneous cell-death phenotypes. Taken together, our data strongly suggest that AtMCP2d plays a positive regulatory role in biotic and abiotic stress-induced PCD.

Antibiotic selection leads to inadvertent selection of nfxC‐type phenotypic mutants in Pseudomonas aeruginosa

Spontaneous nfxC-type phenotypic mutants of Pseudomonas aeruginosa are characterized by chloramphenicol resistance and increased expression of the multidrug efflux pump, MexEF-OprN. These mutants frequently arise during the propagation of bacteria in laboratory conditions. This study shows that some of the discrepancies in transcriptomic/phenotypic profiles of two rsmA mutants, PAZH13 (rsmA mutant in strain PAO1) and PAKΔrsmA, are due to the nfxC-type nature of PAZH13. This indicates that awareness of the possible occurrence of these spontaneous nfxC-type phenotypes is necessary. Screening of mexE levels could provide clarity when an nfxC-type phenotype is suspected.

Maternal alcohol use and medically indicated vs. spontaneous preterm birth outcomes: a population-based study

The aetiology of preterm birth remains poorly understood. The purpose of this study is to investigate if an association exists between prenatal alcohol consumption and preterm birth and to determine if such an association differs by subcategories of preterm birth. We employed vital statistics data from the state of Missouri covering the period 1989-2005 (n = 1 221 677 singleton records). The outcome of interest was preterm birth, subclassified into medically indicated and spontaneous phenotypes. Multivariate logistic regression was used to generate adjusted odds ratios, with non-drinking mothers as the referent category. Prenatal alcohol use was associated with elevated risk for preterm birth. The strength of association was more prominent for spontaneous preterm delivery {adjusted odds ratio (AOR) [95% confidence interval (CI)] = 1.34 (1.28-1.41)} than for medically indicated preterm birth [AOR (95% CI) = 1.16 (1.05-1.28)]. The overall risk for drinking-related spontaneous preterm birth increased with incremental rise in the number of drinks consumed per week (P for trend < 0.01). Prenatal alcohol use is a risk factor for preterm delivery, and especially for spontaneous preterm birth. These findings enhance our understanding of the aetiology of preterm birth and could be utilized in the development of appropriate prevention strategies that will assist in decreasing perinatal mortality and morbidity associated with preterm delivery.

Role of TRPV3 in immune response to development of dermatitis

BackgroundRecently, it has been reported that the Gly573Ser substitution of transient receptor potential V3 (TRPV3) leads to increased ion-channel activity in keratinocytes. Our previous studies have indicated that the spontaneous hairless and dermatitis phenotypes of DS-Nh mice, which were newly established as an animal model of atopic dermatitis (AD), are caused by TRPV3Gly573Ser. Although this substitution causes hairlessness in several kinds of rodents, in our investigations, dermatitis developed in only a few animals. Here, we generated NC/Nga-Nh mice to elucidate the role of TRPV3Gly573Ser in NC/Nga mice, which is one of the most studied animal models of AD.MethodsTo establish and validate the new AD animal model, NC/Nga-Nh mice were generated using NC/Nga and DS-Nh mice, and their clinical features were compared. Next, T-cell receptor (TCR) Vβ usage in splenocytes, evaluation of bacterial colonization, and serological and histological analyses were carried out. Finally, repeated-hapten-application dermatitis was induced in these mice.ResultsNC/Nga-Nh mice did not develop spontaneous dermatitis, whereas DS-Nh mice displayed this phenotype when maintained under the same conditions. Serological analysis indicated that there really was a phenotypic difference between these mice, and TCR repertoire analysis indicated that TCRVβ haplotypes played an important role in the development of dermatitis. Artificial dermatitis developed in DS and NC/Nga-Nh mice, but not in DS-Nh and NC/Nga mice. Histological and serological analyses indicated that mouse strains were listed in descending order of number of skin mast cells: DS-Nh > DS ≈ NC/Nga-Nh > NC/Nga, and serum IgE levels were increased after 2,4,6 trinitrochlorobenzene application in these mice. Serum IgE level in DS-Nh mice was lower than that mesured in other strains.ConclusionOur results confirm the contribution of the TRPV3Gly573Ser gene to the development of repeated hapten dermatitis, but not spontaneous dermatitis in NC/Nga mice.

A FVII Deficiency Induces Cardiac Fibrosis in Mice Resulting in Systolic and Diastolic Dysfunction.

Mice severely deficient in coagulation Factor (F)VII that survive to adulthood have been developed, thus allowing the study of spontaneous bleeding and inflammatory phenotypes under conditions of a deficiency of extrinsic coagulation, especially in organs e.g., the heart, that continually undergo normal mechanical challenge. Mice genetically modified to produce very low levels (∼1% of wild-type) of coagulation FVII (FVIItTA/tTA) spontaneously developed heart abnormalities that were revealed by echocardiography. There were no significant differences between groups at baseline for the hemodynamic and respiratory parameters: temperature and heart rate (HR). The end-systolic functions of FVIItTA/tTA mice heart were comparable to wild-type (WT) controls. However, there were significant changes in the end-diastolic parameters of FVIItTA/tTA hearts. The diameter at end-diastole in FVIItTA/tTA mice was smaller compared to WT mice, which was due to the stiffness of the interventricular wall. When viewed from the parasternal short-axis, these mice had evidence of hypokinesis, indicating alteration of the elastic properties of the left ventricular (LV) wall. Correspondingly, the stroke volume, ejection fraction, fractional shortening, and cardiac output were lower in FVIItTA/tTA mice, compared to WT mice. Mitral valve inflow was compromised in FVIItTA/tTA mice, as demonstrated by the reduced early/late (E/A) filling ratio. We found that the spontaneous impaired cardiac function in FVIItTA/tTA mice was associated with an increased ratio of heart weight to body weight. Decreases in ventricular size, accompanied by reductions in systolic and diastolic functions, suggest a restrictive cardiomyopathy, consistent with an infiltrative myopathic process. Microscopic analysis of mouse hearts showed severe patchy fibrosis in FVIItTA/tTA mice. Hemosiderin deposition in hearts of these mice, along with large increases in inflammatory cells, ultimately resulting in widespread collagen deposition, were found. Significant increases in mRNA levels of TGF-beta, TNF-alpha, and a variety of matrix metalloproteinases, beginning at early ages in FVIItTA/tTA mice, supported the fibrotic pathology. The results of this study demonstrated that hemorrhagic and inflammatory responses to a severe FVII deficiency resulted in the development of cardiac fibrosis, manifest echocardiographically as a restrictive cardiomyopathy, with significantly compromised ventricular diastolic and systolic functions. These data also suggest that a FVII deficiency differentially regulates the expression level of inflammation and extracellular matrix proteins, which result in compromised cardiac function.

Reduced metastasis of transgenic mammary cancer in urokinase-deficient mice.

A prominent phenotype of plasmin deficiency in mice is reduced metastasis in the MMTV-PymT transgenic breast cancer model. Proteolytically active plasmin is generated from inactive plasminogen by one of 2 activators, uPA or tPA. We now find that uPA deficiency alone significantly reduces metastasis >7-fold in the MMTV-PymT model. We studied a cohort of 55 MMTV-PymT transgenic mice, either uPA-deficient or wild-type controls. Tumor incidence, latency, growth rate and final primary tumor burden were not significantly affected by uPA deficiency. In contrast, average lung metastasis volume was reduced from 1.58 mm(3) in wild-type controls to 0.21 mm(3) in uPA-deficient mice (p = 0.023). Tumor cell dissemination to brachial lymph nodes was also reduced from 53% (28/53) in wild-type controls to 31% (17/54) in uPA-deficient mice (p = 0.032). Mice without plasminogen display a severe pleiotropic phenotype. By comparison, spontaneous phenotypes are modest in uPA-deficient mice, probably because they still have active tPA. We show that metastasis is strongly and selectively decreased in uPA-deficient mice, suggesting that uPA-directed antimetastatic therapy would be efficacious and have limited side effects.

The link between 20S proteasome activity and post-replication DNA repair in Saccharomyces cerevisiae.

We have shown previously that deletion of the Saccharomyces cerevisiae UMP1 gene encoding the 20S proteasome maturase causes sensitivity to UV radiation. In the current report, we have extended this finding to show that mutations specifically compromising chymotrypsin-like or trypsin-like activity of 20S proteasome peptidases also result in increased UV sensitivity. We have also established that mutations affecting proteasome activity, namely ump1Delta, pre2-K108R and pup1-T20A, result in spontaneous and UV-induced mutator phenotypes. To elucidate the origin of these DNA repair phenotypes of the proteasomal mutants, we performed epistasis analysis, with respect to UV sensitivity, using yeast strains with the UMP1 deletion in different DNA repair backgrounds. We show that UMP1 is not epistatic to RAD23 and RAD2, which are involved in the nucleotide excision repair (NER) pathway. Instead, our results indicate that UMP1 as well as PUP1 and PRE2 (encoding catalytic subunits of 20S proteasome) belong to an epistatic group of genes functioning in post-replication DNA repair (PRR) and are hypostatic to RAD18, which, in complex with RAD6, plays a central role in PRR. We also show that UMP1 is epistatic to REV3 and RAD30, although the relationship of UMP1 with these genes is different.

Herpes simplex virus type 1 mutants containing the KOS strain ICP34.5 gene in place of the McKrae ICP34.5 gene have McKrae-like spontaneous reactivation but non-McKrae-like virulence.

Herpes simplex virus type 1 (HSV-1) strain McKrae is neurovirulent in rabbits infected by the ocular route, causing fatal encephalitis in approximately 50% of the animals, and has a high-level spontaneous reactivation phenotype, with 10% of rabbit eyes containing reactivated virus at any given time. In contrast, HSV-1 strain KOS is completely avirulent (no rabbits die) and has a completely negative spontaneous reactivation phenotype. Mutations of the ICP34.5 gene can reduce the neurovirulence of HSV-1 strains McKrae and 17syn(+) by up to 100000-fold. ICP34.5 mutants also have reduced spontaneous reactivation phenotypes. To determine whether differences in the ICP34.5 gene might be involved in the reduced neurovirulence and spontaneous reactivation phenotypes of KOS compared with McKrae, we constructed chimeric viruses containing the KOS ICP34.5 gene in place of the McKrae ICP34.5 gene. Rabbits ocularly infected with the chimeric viruses had a high spontaneous reactivation phenotype indistinguishable from McKrae. In contrast, neurovirulence of the chimeric viruses was decreased compared with McKrae. Thus, one or more 'defects' in the KOS ICP34.5 gene appeared to be at least partially responsible for the reduced neurovirulence of KOS compared with McKrae. However, there appeared to be no 'defect' in the KOS ICP34.5 function required for efficient spontaneous reactivation.

UV Irradiation Causes the Loss of Viable Mitotic Recombinants in Schizosaccharomyces pombe Cells Lacking the G2/M DNA Damage Checkpoint

Abstract Elevated mitotic recombination and cell cycle delays are two of the cellular responses to UV-induced DNA damage. Cell cycle delays in response to DNA damage are mediated via checkpoint proteins. Two distinct DNA damage checkpoints have been characterized in Schizosaccharomyces pombe: an intra-S-phase checkpoint slows replication and a G2/M checkpoint stops cells passing from G2 into mitosis. In this study we have sought to determine whether UV damage-induced mitotic intrachromosomal recombination relies on damage-induced cell cycle delays. The spontaneous and UV-induced recombination phenotypes were determined for checkpoint mutants lacking the intra-S and/or the G2/M checkpoint. Spontaneous mitotic recombinants are thought to arise due to endogenous DNA damage and/or intrinsic stalling of replication forks. Cells lacking only the intra-S checkpoint exhibited no UV-induced increase in the frequency of recombinants above spontaneous levels. Mutants lacking the G2/M checkpoint exhibited a novel phenotype; following UV irradiation the recombinant frequency fell below the frequency of spontaneous recombinants. This implies that, as well as UV-induced recombinants, spontaneous recombinants are also lost in G2/M mutants after UV irradiation. Therefore, as well as lack of time for DNA repair, loss of spontaneous and damage-induced recombinants also contributes to cell death in UV-irradiated G2/M checkpoint mutants.

Pathways and bottlenecks in the web of inflammatory adhesion molecules and chemoattractants.

Leukocyte recruitment requires capture, rolling, activation, adhesion, and transmigration. Adhesion molecules and chemoattractants have been identified that mediate each of these steps. Their functions often overlap, but the combined absence of some molecules can lead to severe spontaneous phenotypes, as seen in CD18-/- mice, or early lethality, as in CD18-/- E-selectin-/- mice. These groups of molecules define bottlenecks that restrict the inflammatory response. Adhesion molecules and activation mechanisms can also form groups of preferential usage, or pathways. Based on these findings, a web-like model may represent the inflammatory process better than the linear cascade model. Bottlenecks and pathways depend on the degree and nature of overlapping functions, the disease process, tissue site, and the inflammatory stimulus.