Multiple reorganizations of the lateral elements of the synaptonemal complex facilitate homolog segregation in Bombyx mori oocytes

Although Lepidopteran females build a synaptonemal complex (SC) in pachytene, homologs do not crossover, necessitating an alternative method of homolog conjunction. In Bombyx mori oocytes, the SC breaks down at the end of pachytene, and homolog associations are maintained by a large oocyte-specific structure, which we call the bivalent bridge (BB), connecting paired homologs. The BB is derived from at least some components of the SC lateral elements (LEs). It contains the HORMAD protein HOP1 and the LE protein SYCP2 and is formed by the fusion of the two LE derivatives. As diplotene progresses, the BB increases in width and acquires a layered structure with a thick band of HOP1 separating two layers of SYCP2. The HOP1 interacting protein, PCH2, joins the BB in mid-diplotene, and by late-diplotene, it lies in the middle of the HOP1 filament. This structure is maintained through metaphase I. SYCP2 and PCH2 are lost at anaphase I, and the BB no longer connects the separating homologs. However, a key component of the BB, HOP1, remains at the metaphase I plate. These changes in organization of the BB occur simultaneously with the movement of the kinetochore protein, DSN1, from within the BB at mid-diplotene to the edge of the homologs facing the poles by metaphase I. We view these data in context of models in which SC components and regulators can be repurposed to achieve different functions, a fascinating example of evolution achieving homolog conjunction in an alternative way with recycling of SC proteins.

Defining a core configuration for human centromeres during mitosis

The centromere components cohesin, CENP-A, and centromeric DNA are essential for biorientation of sister chromatids on the mitotic spindle and accurate sister chromatid segregation. Insight into the 3D organization of centromere components would help resolve how centromeres function on the mitotic spindle. We use ChIP-seq and super-resolution microscopy with single particle averaging to examine the geometry of essential centromeric components on human chromosomes. Both modalities suggest cohesin is enriched at pericentromeric DNA. CENP-A localizes to a subset of the α-satellite DNA, with clusters separated by ~562 nm and a perpendicular intervening ~190 nM wide axis of cohesin in metaphase chromosomes. Differently sized α-satellite arrays achieve a similar core structure. Here we present a working model for a common core configuration of essential centromeric components that includes CENP-A nucleosomes, α-satellite DNA and pericentromeric cohesion. This configuration helps reconcile how centromeres function and serves as a foundation to add components of the chromosome segregation machinery.

rRNA transcription is integral to phase separation and maintenance of nucleolar structure

Transcription of ribosomal RNA (rRNA) by RNA Polymerase (Pol) I in the nucleolus is necessary for ribosome biogenesis, which is intimately tied to cell growth and proliferation. Perturbation of ribosome biogenesis results in tissue specific disorders termed ribosomopathies in association with alterations in nucleolar structure. However, how rRNA transcription and ribosome biogenesis regulate nucleolar structure during normal development and in the pathogenesis of disease remains poorly understood. Here we show that homozygous null mutations in Pol I subunits required for rRNA transcription and ribosome biogenesis lead to preimplantation lethality. Moreover, we discovered that Polr1a-/-, Polr1b-/-, Polr1c-/- and Polr1d-/- mutants exhibit defects in the structure of their nucleoli, as evidenced by a decrease in number of nucleolar precursor bodies and a concomitant increase in nucleolar volume, which results in a single condensed nucleolus. Pharmacological inhibition of Pol I in preimplantation and midgestation embryos, as well as in hiPSCs, similarly results in a single condensed nucleolus or fragmented nucleoli. We find that when Pol I function and rRNA transcription is inhibited, the viscosity of the granular compartment of the nucleolus increases, which disrupts its phase separation properties, leading to a single condensed nucleolus. However, if a cell progresses through mitosis, the absence of rRNA transcription prevents reassembly of the nucleolus and manifests as fragmented nucleoli. Taken together, our data suggests that Pol I function and rRNA transcription are required for maintaining nucleolar structure and integrity during development and in the pathogenesis of disease.

Shared retinoic acid responsive enhancers coordinately regulate nascent transcription of Hoxb coding and non-coding RNAs in the developing mouse neural tube

Signaling pathways regulate the patterns of Hox gene expression that underlie their functions in the specification of axial identity. Little is known about the properties of cis-regulatory elements and underlying transcriptional mechanisms that integrate graded signaling inputs to coordinately control Hox expression. Here, we optimized a single molecule fluorescent in situ hybridization (smFISH) technique with probes spanning introns to evaluate how three shared retinoic acid response element (RARE)-dependent enhancers in the Hoxb cluster regulate patterns of nascent transcription in vivo at the level of single cells in wild-type and mutant embryos. We predominately detect nascent transcription of only a single Hoxb gene in each cell, with no evidence for simultaneous co-transcriptional coupling of all or specific subsets of genes. Single and/or compound RARE mutations indicate that each enhancer differentially impacts global and local patterns of nascent transcription, suggesting that selectivity and competitive interactions between these enhancers is important to robustly maintain the proper levels and patterns of nascent Hoxb transcription. This implies that rapid and dynamic regulatory interactions potentiate transcription of genes through combined inputs from these enhancers in coordinating the retinoic acid response.

Defining a core configuration for human centromeres during mitosis

The biorientation of sister chromatids on the mitotic spindle, essential for accurate sister chromatid segregation, relies on critical centromere components including cohesin, the centromere-specific H3 variant CENP-A, and centromeric DNA. Centromeric DNA is highly variable between chromosomes yet must accomplish a similar function. Moreover, how the 50 nm cohesin ring, proposed to encircle sister chromatids, accommodates inter-sister centromeric distances of hundreds of nanometers on the metaphase spindle is a conundrum. Insight into the 3D organization of centromere components would help resolve how centromeres function on the mitotic spindle. We used ChIP-seq and super-resolution microscopy to examine the geometry of essential centromeric components on human chromosomes. ChIP-seq demonstrates that cohesin subunits are depleted in α-satellite arrays where CENP-A nucleosomes and kinetochores assemble. Cohesin is instead enriched at pericentromeric DNA. Structured illumination microscopy of sister centromeres is consistent, revealing a non-overlapping pattern of CENP-A and cohesin. We used single particle averaging of hundreds of mitotic sister chromatids to develop an average centromere model. CENP-A clusters on sister chromatids, connected by α-satellite, are separated by ~562 nm with a perpendicular intervening ~190 nM wide axis of cohesin. Two differently sized α-satellite arrays on chromosome 7 display similar inter-sister CENP-A cluster distance, demonstrating different sized arrays can achieve a common spacing. Our data suggest a working model for a common core configuration of essential centromeric components that includes CENP-A nucleosomes at the outer edge of extensible α-satellite DNA and pericentromeric cohesion. This configuration helps reconcile how centromeres function and serves as a foundation for future studies of additional components required for centromere function.

c-Myc promotes polyploidy in murine trophoblast cells and suppresses senescence

The placenta is essential for reproductive success. The murine placenta includes polyploid giant cells that are crucial for its function. Polyploidy occurs broadly in nature but the regulators and significance in the placenta are unknown. We discovered that many murine placental cell types are polyploid. We identified factors that license polyploidy using single-cell RNA seq. c-Myc is a key regulator of polyploidy and placental development and is required for multiple rounds of DNA replication, likely via endocycles, in trophoblast giant cells. Furthermore, c-MYC supports the expression of DNA replication and nucleotide biosynthesis genes along with ribosomal RNA. Increased DNA damage and senescence occur in trophoblast giant cells without c-Myc, accompanied by senescence in the neighboring maternal decidua. These data reveal c-Myc is essential for polyploidy to support normal placental development, thereby preventing premature senescence. Our study combined with the literature suggests c-Myc is an evolutionarily conserved regulator of polyploidy.

Cell-type profiling of the sympathetic nervous system using spatial transcriptomics and spatial mapping of mRNA

BACKGROUND

The molecular identification of neural progenitor cell populations that connect to establish the sympathetic nervous system (SNS) remains unclear. This is due to technical limitations in the acquisition and spatial mapping of molecular information to tissue architecture.

RESULTS

To address this, we applied Slide-seq spatial transcriptomics to intact fresh frozen chick trunk tissue transversely cryo-sectioned at the developmental stage prior to SNS formation. In parallel, we performed age- and location-matched single cell (sc) RNA-seq and 10× Genomics Visium to inform our analysis. Downstream bioinformatic analyses led to the unique molecular identification of neural progenitor cells within the peripheral sympathetic ganglia (SG) and spinal cord preganglionic neurons (PGNs). We then successfully applied the HiPlex RNAscope fluorescence in situ hybridization and multispectral confocal microscopy to visualize 12 gene targets in stage-, age- and location-matched chick trunk tissue sections.

CONCLUSIONS

Together, these data demonstrate a robust strategy to acquire and integrate single cell and spatial transcriptomic information, resulting in improved resolution of molecular heterogeneities in complex neural tissue architectures. Successful application of this strategy to the developing SNS provides a roadmap for functional studies of neural connectivity and platform to address complex questions in neural development and regeneration.

Identification and Localization of Cell Types in the Mouse Olfactory Bulb Using Slide-SeqV2

Spatial transcriptomics maps RNA molecules to the location in a tissue where they are expressed. Here we document the use of Slide-SeqV2 to visualize gene expression in the mouse olfactory bulb (OB). This approach relies on spatially identified beads to locate and quantify individual transcripts. The expression profiles associated with the beads are used to identify and localize individual cell types in an unbiased manner. We demonstrate the various cell types and subtypes with distinct spatial locations in the olfactory bulb that are identified using Slide-SeqV2.

Persistent DNA Damage and Senescence in the Placenta Impacts Developmental Outcomes of Embryos

Cohesin is an evolutionarily conserved chromosome-associated protein complex essential for chromosome segregation, gene expression, and repair of DNA damage. Mutations that affect this complex cause the human developmental disorder Cornelia de Lange syndrome (CdLS), thought to arise from defective embryonic transcription. We establish a significant role for placental defects in the development of CdLS mouse embryos (Nipbl and Hdac8). Placenta is a naturally senescent tissue; we demonstrate that persistent DNA damage potentiates senescence and activates cytokine signaling. Mutant embryo developmental outcomes are significantly improved in the context of a wild-type placenta or by genetically restricting cytokine signaling. Our study highlights that cohesin is required for maintaining ploidy and the repair of spontaneous DNA damage in placental cells, suggesting that genotoxic stress and ensuing placental senescence and cytokine production could represent a broad theme in embryo health and viability.

Yeast centrosome components form a noncanonical LINC complex at the nuclear envelope insertion site

How the nuclear envelope is remodeled to facilitate insertion of large protein complexes is poorly understood. Chen et al. use superresolution imaging with bimolecular fluorescence complementation to show that a novel noncanonical linker of nucleoskeleton and cytoskeleton (LINC) complex forms at sites of nuclear envelope fenestration in yeast.

Bipolar spindle formation in yeast requires insertion of centrosomes (known as spindle pole bodies [SPBs]) into fenestrated regions of the nuclear envelope (NE). Using structured illumination microscopy and bimolecular fluorescence complementation, we map protein distribution at SPB fenestrae and interrogate protein–protein interactions with high spatial resolution. We find that the Sad1-UNC-84 (SUN) protein Mps3 forms a ring-like structure around the SPB, similar to toroids seen for components of the SPB insertion network (SPIN). Mps3 and the SPIN component Mps2 (a Klarsicht-ANC-1-Syne-1 domain [KASH]–like protein) form a novel noncanonical linker of nucleoskeleton and cytoskeleton (LINC) complex that is connected in both luminal and extraluminal domains at the site of SPB insertion. The LINC complex also controls the distribution of a soluble SPIN component Bbp1. Taken together, our work shows that Mps3 is a fifth SPIN component and suggests both direct and indirect roles for the LINC complex in NE remodeling.

Abstract GS3-06: Dynamics of breast cancer relapse reveal molecularly defined late recurring ER-positive subgroups: Results from the METABRIC study

Background: Recent studies have demonstrated that women with early stage ER-positive (ER+) and HER2-negative (HER2-) breast cancer have a persistent risk of recurrence and cancer related death up to 20 years post diagnosis, highlighting the chronic nature of ER+ breast cancer and critical need to identify tumor characteristics that are more predictive of risk of recurrence than standard clinical covariates. However, progress in delineating the dynamics of breast cancer relapse and biomarkers of late recurrence has been hindered by the lack of large cohorts with long-term clinical follow-up and molecular information.

Methods: We report the results of a cohort of 3,240 breast cancer patients from the United Kingdom and Canada with 20 years of follow-up (median 9.75 years), including 1,980 with accompanying molecular data from the primary breast tumor. Information for each patient on loco-regional recurrence (LR), distant recurrence (DR), and site(s) of metastases was collected. We developed a non-homogenous Markov chain model that accounted for different clinical endpoints and timescales, as well as competing risks of mortality and the distinct baseline hazards that characterize different molecular subgroups. This approach enabled robust analysis of the spatio-temporal dynamics of breast cancer recurrence across the clinical subgroups, PAM50 subgroups and the integrative clusters, while also enabling individual risk of relapse predictions.

Results: We employed our multistate model to compute the probability of experiencing a LR or DR, as well as the baseline transition probabilities from surgery, LR or DR at various time intervals for average individuals in each of the clinical/molecular subgroups. These analyses reveal four late-recurring ER+ (predominantly HER2-) subgroups, together accounting for 26% of all ER+ tumors, with high (median 42-55%) risk of recurrence up to 20 years post-diagnosis. Each of these four subgroups maps to one of the Integrative Clusters, defined based on genomic copy number alterations and gene expression, and is enriched for a characteristic copy number amplification events: 11q13 (CCND1, RSF1), 8p12 (FGFR1, ZNF703), 17q23 (RPS6KB1) and 8q24 (MYC). These four molecular subgroups are superior in predicting late DR than standard clinical variables.

Conclusions: A detailed understanding of the rates and routes of metastasis and their variability across the distinct molecular subtypes is essential for devising personalized approaches to breast cancer care. We describe a molecularly characterized breast cancer cohort with long-term clinical follow-up and a statistical modeling framework, enabling delineation of the dynamics of breast cancer recurrence at unprecedented resolution. These analyses reveal four late recurring ER+ subgroups and accompanying biomarkers that collectively define the quarter of ER+ cases at highest risk of recurrence. Our findings highlight opportunities for improved patient stratification and biomarker-driven clinical trials directed at the subset of breast cancer patients with persistent risk of recurrence.

Citation Format: Curtis C, Rueda OM, Sammut S-J, Chin S-F, Caswell-Jin JL, Seoane JA, Callari M, Batra R, Pereira B, Bruna A, Ali HR, Provenzano E, Liu B, Parisien M, Gillett C, McKinney S, Green A, Murphy L, Purushotham A, Ellis I, Pharoah P, Rueda C, Aparicio S, Caldas C. Dynamics of breast cancer relapse reveal molecularly defined late recurring ER-positive subgroups: Results from the METABRIC study [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr GS3-06.

Antimicrobial peptides modulate long-term memory

Antimicrobial peptides act as a host defense mechanism and regulate the commensal microbiome. To obtain a comprehensive view of genes contributing to long-term memory we performed mRNA sequencing from single Drosophila heads following behavioral training that produces long-lasting memory. Surprisingly, we found that Diptericin B, an immune peptide with antimicrobial activity, is upregulated following behavioral training. Deletion and knock down experiments revealed that Diptericin B and another immune peptide, Gram-Negative Bacteria Binding Protein like 3, regulate long-term but not short-term memory or instinctive behavior in Drosophila. Interestingly, removal of DptB in the head fat body and GNBP-like3 in neurons results in memory deficit. That putative antimicrobial peptides influence memory provides an example of how some immune peptides may have been repurposed to influence the function of nervous system.

It is becoming evident that the nervous system and immune system share not only some of the same molecular logic but also the same components. Here, we report a novel and unanticipated example of how immune genes influence nervous system function. Exploring how Drosophila form long-lasting memories of certain experiences, we have found that antimicrobial peptides that fight bacteria in the body, are expressed in the head, and control whether an animal will form long-term memory of a food source or an unsuccessful mating experience. Antimicrobial peptides are detected in the brain of many species and has often been associated with dysfunction of the nervous system. This and other recent works, provide an explanation to why antimicrobial peptides may be expressed in the head: they regulate normal functions of the brain. Both eating, and mating engage the immune system in preparation of exposure to external agents including bacteria. We speculate antimicrobial peptides were upregulated in the body to deal with immune challenges and over evolutionary time some of them are co-adopted to activate signaling pathways to convey specific information to the nervous system.

An adaptable chromosome preparation methodology for use in invertebrate research organisms

Background

The ability to efficiently visualize and manipulate chromosomes is fundamental to understanding the genome architecture of organisms. Conventional chromosome preparation protocols developed for mammalian cells and those relying on species-specific conditions are not suitable for many invertebrates. Hence, a simple and inexpensive chromosome preparation protocol, adaptable to multiple invertebrate species, is needed.

Results

We optimized a chromosome preparation protocol and applied it to several planarian species (phylum Platyhelminthes), the freshwater apple snail Pomacea canaliculata (phylum Mollusca), and the starlet sea anemone Nematostella vectensis (phylum Cnidaria). We demonstrated that both mitotically active adult tissues and embryos can be used as sources of metaphase chromosomes, expanding the potential use of this technique to invertebrates lacking cell lines and/or with limited access to the complete life cycle. Simple hypotonic treatment with deionized water was sufficient for karyotyping; growing cells in culture was not necessary. The obtained karyotypes allowed the identification of differences in ploidy and chromosome architecture among otherwise morphologically indistinguishable organisms, as in the case of a mixed population of planarians collected in the wild. Furthermore, we showed that in all tested organisms representing three different phyla this protocol could be effectively coupled with downstream applications, such as chromosome fluorescent in situ hybridization.

Conclusions

Our simple and inexpensive chromosome preparation protocol can be readily adapted to new invertebrate research organisms to accelerate the discovery of novel genomic patterns across the branches of the tree of life.

Interventions for enhancing return to work in individuals with a common mental illness: systematic review and meta-analysis of randomized controlled trials

Common mental disorders (CMDs) are highly prevalent in the working population, and are associated with long-term sickness absence and disability. Workers on sick leave with CMDs would benefit from interventions that enable them to successfully return to work (RTW). However, the effectiveness of RTW interventions for workers with a CMD is not well studied. The objective of this review is to assess the effectiveness of existing workplace and clinical interventions that were aimed at enhancing RTW. A systematic review of studies of interventions for improving RTW in workers with a CMD was conducted. The main outcomes were proportion of RTW and sick-leave duration until RTW. Randomized controlled trials (RCTs) were identified from Medline/PubMed, PsycINFO, EMBASE, SocINDEX, and Human resource and management databases from January 1995 to 2016. Two authors independently selected studies, assessed risk of bias and extracted data. We pooled studies that we deemed sufficiently homogeneous in different comparison groups and assessed the overall quality of the evidence. We reviewed 2347 abstracts from which 136 full-text articles were reviewed and 16 RCTs were included in the analysis. Combined results from these studies suggested that the available interventions did not lead to improved RTW rates over the control group [pooled risk ratio 1.05, 95% confidence interval (CI) 0.97-1.12], but reduced the number of sick-leave days in the intervention group compared to the control group, with a mean difference of -13.38 days (95% CI -24.07 to -2.69).

Internal medicine trainees' views of training adequacy and duty hours restrictions in 2009

PURPOSE

To gauge internal medicine (IM) trainees' perceptions regarding aspects of their inpatient rotations, including supervision, educational opportunities, the perceived effect of duty hours regulations on quality of patient care, the causes of medical errors, and sleep.

METHOD

The authors analyzed the results of questionnaires administered to trainees following the October 2009 in-training examinations (ITE).

RESULTS

Of the 21,768 IM trainees in postgraduate years 1 through 3 who took the IM-ITE, 18,272 (83.9%) responded. The majority of these trainees (87.7%) reported that supervision was adequate, and nearly half (46.3%) reported insufficient or minimal time to participate in learning activities. Two-thirds or more thought that specific work regulations such as limited shift length and more time off after nights and extended shifts would at least "occasionally," if not "usually" or "always," improve patient care. IM trainees at least "occasionally" attributed errors to workload (68.8% of respondents), fatigue (66.9%), inexperience or lack of knowledge (61.0%), incomplete handoffs (60.2%), and insufficient ancillary staff (53.5%). IM trainees' sleep hours were limited during extended and overnight shifts.

CONCLUSIONS

IM trainees agree that limited educational opportunities are the weakest part of the average inpatient rotation. Few have complaints about the adequacy of supervision. These trainees' optimism regarding the positive influence of potential work hours restrictions on patient care and their views of likely causes of medical errors suggest the need for innovative patient care schedules and education curricula.

Identifying stromal-epithelial interactions in the mammary gland through genome-wide siRNA screening

Abstract #101

Stromal-epithelial interactions have been implicated in all stages of mammary gland development and malignancy. Although stromal composition is dynamic over time, fibroblasts account for a large proportion of the cellular compartment. The relationship between the fibroblasts and the mammary epithelial cells hitherto remains ill defined. A striking example of the relationship between the two cell types lies in the obligatory requirement for fibroblasts in the Colony Forming Assay (CFC assay). When plated with irradiated fibroblasts, mammary epithelial cells obtained from dissociated normal tissues are able to form colonies containing either all myoepithelial cells, all luminal cells or both. Mixed colonies represent derivation from bipotent progenitor cells, the most primitive detectable cell within the breast lineage hierarchy.
 The fibroblast dependency exhibited by primitive cells within the CFC assay is mimicked by the 184-hTERT cell line. This is a heterogeneous normal mammary epithelial cell line immortalized through the forced expression of human telomerase. A series of clonal cell lines was derived from the earliest available passage of 184-hTERT cells and 14 unique telomerase integration sites were found amongst the original cells. Interestingly, all of these clonal lines have the propensity to selectively gain chromosome 20 during passaging. Copy number gain of chromosome 20 is associated with poor clinical prognosis in breast cancer and is thought to play a role in oncogenic progression.
 A genome-wide siRNA screen has been completed targeting the 184-hTERT cells in a modified CFC assay to identify genes that are involved in fibroblast dependant growth. The screen was done in parallel using an early passage diploid 184-hTERT clonal line and a later passage (48,XX,+20,+20) clonal line. Dharmacon's human siGENOME library was used to individually interrogate approximately 22,000 genes found within the NCBI RefSeq database. Effects on fibroblast dependant growth were established through cell counts derived from images collected on GE's InCell Analyzer and segmented using Cell Profiler. 4225 genes showed conservative statistically significant evidence of difference in cell counts using the Bonferroni-Holm multiple comparisons method in both or either of the cell lines. Of these, 534 have an annotated location on the plasma membrane. Receptors to obligatory media components including Insulin, EGF and Transferrin were captured in this dataset. Not all of these genes will be specific to fibroblast dependant growth and thus the cognate ligands to these targets have been identified and are currently being manipulated in the fibroblasts. Modified fibroblasts will be used in the CFC assay to judge effects on mammary progenitor cell growth and will be co-cultured with carcinoma cells to evaluate effects on proliferation. This global assessment of the interactions between normal and malignant epithelial cells with fibroblasts has broad spanning implications ranging from the culturing of mammary progenitor cells to therapeutic target selection.

Citation Information: Cancer Res 2009;69(2 Suppl):Abstract nr 101.

New cutpoints to identify increased HER2 copy number: analysis of a large, population-based cohort with long-term follow-up

BACKGROUND

HER2 gene amplification and/or protein overexpression in breast cancer is associated with a poor prognosis and predicts response to anti-HER2 therapy. We examine the natural history of breast cancers in relationship to increased HER2 copy numbers in a large population-based study.

PATIENTS AND METHODS

HER2 status was measured by fluorescence in situ hybridization (FISH) and immunohistochemistry (IHC) in approximately 1,400 breast cancer cases with greater than 15 years of follow-up. Protein expression was evaluated with two different commercially-available antibodies.

RESULTS

We looked for subgroups of breast cancer with different clinical outcomes, based on HER2 FISH amplification ratio. The current HER2 ratio cut point for classifying HER2 positive and negative cases is 2.2. However, we found an increased risk of disease-specific death associated with FISH ratios of >1.5. An 'intermediate' group of cases with HER2 ratios between 1.5 and 2.2 was found to have a significantly better outcome than the conventional 'amplified' group (HER2 ratio >2.2) but a significantly worse outcome than groups with FISH ratios less than 1.5.

CONCLUSION

Breast cancers with increased HER2 copy numbers (low level HER2 amplification), below the currently accepted positive threshold ratio of 2.2, showed a distinct, intermediate outcome when compared to HER2 unamplified tumors and tumors with HER2 ratios greater than 2.2. These findings suggest that a new cut point to determine HER2 positivity, at a ratio of 1.5 (well below the current recommended cut point of 2.2), should be evaluated.

Gamma-aminobutyric acid type A receptors modulate cAMP-mediated long-term potentiation and long-term depression at monosynaptic CA3-CA1 synapses

cAMP induces a protein-synthesis-dependent late phase of long-term potentiation (LTP) at CA3-CA1 synapses in acute hippocampal slices. Herein we report cAMP-mediated LTP and long-term depression (LTD) at monosynaptic CA3-CA1 cell pairs in organotypic hippocampal slice cultures. After bath application of the membrane-permeable cAMP analog adenosine 3',5'-cyclic monophosphorothioate, Sp isomer (Sp-cAMPS), synaptic transmission was enhanced for at least 2 h. Consistent with previous findings, the late phase of LTP requires activation of cAMP-dependent protein kinase A and protein synthesis. There is also an early phase of LTP induced by cAMP; the early phase depends on protein kinase A but, in contrast to the later phase, does not require protein synthesis. In addition, the cAMP-induced LTP is associated with a reduction of paired-pulse facilitation, suggesting that presynaptic modification may be involved. Furthermore, we found that Sp-cAMPS induced LTD in slices pretreated with picrotoxin, a gamma-aminobutyric acid type A (GABA(A)) receptor antagonist. This form of LTD depends on protein synthesis and protein phosphatase(s) and is accompanied by an increased ratio of failed synaptic transmission. These results suggest that GABA(A) receptors can modulate the effect of cAMP on synaptic transmission and thus determine the direction of synaptic plasticity.

High spatial resolution measurements of organ blood flow in small laboratory animals

With the use of a newly developed Imaging Cryomicrotome to determine the spatial location of fluorescent microspheres in organs, we validate and report our processing algorithms for measuring regional blood flow in small laboratory animals. Microspheres (15-microm diameter) of four different fluorescent colors and one radioactive label were simultaneously injected into the left ventricle of a pig. The heart and kidneys were dissected, and the numbers of fluorescent and radioactive microspheres were determined in 10 randomly selected pieces. All microsphere counts fell well within the 95% expected confidence limits as determined from the radioactive counts. Fluorescent microspheres (15-microm diameter) of four different colors were also injected into the tail vein of a rat and the left ventricle of a rabbit. After correction for Poisson noise, correlation coefficients between the colors were 0.99 +/- 0.02 (means +/- SD) for the rabbit heart and 0.99 +/- 0.02 for the rat lung. Mathematical dissection algorithms, statistics to analyze the spatial data, and methods to visualize blood flow distributions in small animal organs are presented.

ROMK1 (Kir1.1) causes apoptosis and chronic silencing of hippocampal neurons

Lentiviral vectors were constructed to express the weakly rectifying kidney K(+) channel ROMK1 (Kir1.1), either fused to enhanced green fluorescent protein (EGFP) or as a bicistronic message (ROMK1-CITE-EGFP). The channel was stably expressed in cultured rat hippocampal neurons. Infected cells were maintained for 2-4 wk without decrease in expression level or evidence of viral toxicity, although 15.4 mM external KCl was required to prevent apoptosis of neurons expressing functional ROMK1. No other trophic agents tested could prevent cell death, which was probably caused by K(+) loss. This cell death did not occur in glia, which were able to support ROMK1 expression indefinitely. Functional ROMK1, quantified as the nonnative inward current at -144 mV in 5.4 mM external K(+) blockable by 500 microM Ba(2+), ranged from 1 to 40 pA/pF. Infected neurons exhibited a Ba(2+)-induced depolarization of 7 +/- 2 mV relative to matched EGFP-infected controls, as well as a 30% decrease in input resistance and a shift in action potential threshold of 2.6 +/- 0.5 mV. This led to a shift in the relation between injected current and firing frequency, without changes in spike shape, size, or timing. This shift, which quantifies silencing as a function of ROMK1 expression, was predicted from Hodgkin-Huxley models. No cellular compensatory mechanisms in response to expression of ROMK1 were identified, making ROMK1 potentially useful for transgenic studies of silencing and neurodegeneration, although its lethality in normal K(+) has implications for the use of K(+) channels in gene therapy.

Pulmonary NO synthase inhibition and inspired CO2: effects on V'/Q' and pulmonary blood flow distribution

Inhaled carbon dioxide decreases ventilation/perfusion ratio (V'/Q') heterogeneity in dogs. The aim of this study was to test whether inhaled CO2 improves the V'/Q' by inhibition of nitric oxide production and whether inhibition of endogenous NO production in the lung alters gas exchange and V'/Q' matching. Eleven healthy dogs were anaesthetized and mechanically ventilated. The multiple inert gas elimination technique (MIGET) was used to measure V'/Q' heterogeneity and regional pulmonary blood flow heterogeneity was assessed in five dogs using fluorescent microspheres. In a separate set of five dogs, exhaled NO levels were measured via chemiluminescence. All dogs were studied before and after 4.8% inspired CO2, and then given the NO synthase inhibitor N(omega)-nitro-L-arginine methyl ester (L-NAME, 10 mg x kg(-1)) via nebulization, after which they were studied again with room air and inhaled CO2. CO2 and L-NAME improved arterial and alveolar oxygen tension, but the improvements with L-NAME did not reach statistical significance. Improved V'/Q' matching, as assessed by the MIGET, occurred under all experimental conditions. Exhaled NO levels were reduced by 40% with CO2 and 70% with L-NAME. The standard deviation of regional pulmonary blood flow assessed via microspheres decreased only with inhaled CO2. Fractal analysis of pulmonary blood flow distributions revealed that regional blood flow was highly correlated with flow to neighbouring pieces of lung in all four conditions with no changes in the fractal dimension. Inspired carbon dioxide improves ventilation perfusion ratio matching and is associated with a more homogeneous distribution of pulmonary blood flow. Although inspired carbon dioxide causes a reduction in exhaled nitric oxide, the differences in pulmonary perfusion distributions found between carbon dioxide and N(omega)-nitro-L-arginine methyl ester suggest that the carbon dioxide effect is not mediated by a reduction in nitric oxide production. The improved ventilation perfusion ratio matching with inhibition of nitric oxide synthase suggests the intriguing possibility requiring further study that endogenous production of nitric oxide in the lung does not subserve ventilation perfusion ratio regulation.

Exercise alters fractal dimension and spatial correlation of pulmonary blood flow in the horse

We determined the changes in fractal dimensions and spatial correlations of regional pulmonary blood flow with increasing exercise in race horses (n = 4) by using 15-microm fluorescent microspheres. Fluorescence was measured to quantitate regional blood to 1.3-cm(3) samples (n = 1,621-2,503). Perfusion distributions were characterized with fractal dimensions (a measure of spatial variability) and spatial correlations. On average, the fractal dimension decreased with exercise (trot 1.216 to gallop 1.173; P < 0. 05) despite a variable fractal dimension at rest. Spatial correlation of flow to neighboring pieces increased with exercise (trot 0.57 +/- 0.074 to gallop 0.73 +/- 0.051) and was inversely correlated with fractal dimension, indicating better spatial correlation as blood flow distribution becomes more uniform. This is the first study to document a change in fractal dimension as a result of increasing pulmonary blood flow. Spatial differences in response to vasoregulatory mediators may play a role in this phenomenon.

Correlation between ventilation and perfusion determines VA/Q heterogeneity in endotoxemia

Endotoxin increases ventilation-to-perfusion ratio (VA/Q) heterogeneity in the lung, but the precise changes in alveolar ventilation (VA) and perfusion that lead to VA/Q heterogeneity are unknown. The purpose of this study was to determine how endotoxin affects the distributions of ventilation and perfusion and the impact of these changes on VA/Q heterogeneity. Seven anesthetized, mechanically ventilated juvenile pigs were given E. coli endotoxin intravenously, and regional ventilation and perfusion were measured simultaneously by using aerosolized and injected fluorescent microspheres. Endotoxemia significantly decreased the correlation between regional ventilation and perfusion, increased perfusion heterogeneity, and redistributed perfusion between lung regions. In contrast, ventilation heterogeneity did not change, and redistribution of ventilation was modest. The decrease in correlation between regional ventilation and perfusion was responsible for significantly more VA/Q heterogeneity than were changes in ventilation or perfusion heterogeneity. We conclude that VA/Q heterogeneity increases during endotoxemia primarily as a result of the decrease in correlation between regional ventilation and perfusion, which is in turn determined primarily by changes in perfusion.

Fractal nature of regional ventilation distribution

High-resolution measurements of pulmonary perfusion reveal substantial spatial heterogeneity that is fractally distributed. This observation led to the hypothesis that the vascular tree is the principal determinant of regional blood flow. Recent studies using aerosol deposition show similar ventilation heterogeneity that is closely correlated with perfusion. We hypothesize that ventilation has fractal characteristics similar to blood flow. We measured regional ventilation and perfusion with aerosolized and injected fluorescent microspheres in six anesthetized, mechanically ventilated pigs in both prone and supine postures. Adjacent regions were clustered into progressively larger groups. Coefficients of variation were calculated for each cluster size to determine fractal dimensions. At the smallest size lung piece, local ventilation and perfusion are highly correlated, with no significant difference between ventilation and perfusion heterogeneity. On average, the fractal dimension of ventilation is 1.16 in the prone posture and 1. 09 in the supine posture. Ventilation has fractal properties similar to perfusion. Efficient gas exchange is preserved, despite ventilation and perfusion heterogeneity, through close correlation. One potential explanation is the similar geometry of bronchial and vascular structures.

Hemodilution during venous gas embolization improves gas exchange, without altering V(A)/Q or pulmonary blood flow distributions

BACKGROUND

Isovolemic anemia results in improved gas exchange in rabbits with normal lungs but in relatively poorer gas exchange in rabbits with whole-lung atelectasis. In the current study, the authors characterized the effects of hemodilution on gas exchange in a distinct model of diffuse lung injury: venous gas embolization.

METHODS

Twelve anesthetized rabbits were mechanically ventilated at a fixed rate and volume. Gas embolization was induced by continuous infusion of nitrogen via an internal jugular venous catheter. Serial hemodilution was performed in six rabbits by simultaneous withdrawal of blood and infusion of an equal volume of 6% hetastarch; six rabbits were followed as controls over time. Measurements included hemodynamic parameters and blood gases, ventilation-perfusion (V(A)/Q) distribution (multiple inert gas elimination technique), pulmonary blood flow distribution (fluorescent microspheres), and expired nitric oxide (NO; chemoluminescence).

RESULTS

Venous gas embolization resulted in a decrease in partial pressure of arterial oxygen (PaO2) and an increase in partial pressure of arterial carbon dioxide (PaCO2), with markedly abnormal overall V(A)/Q distribution and a predominance of high V(A)/Q areas. Pulmonary blood flow distribution was markedly left-skewed, with low-flow areas predominating. Hematocrit decreased from 30+/-1% to 11+/-1% (mean +/- SE) with hemodilution. The alveolar-arterial PO2 (A-aPO2) difference decreased from 375+/-61 mmHg at 30% hematocrit to 218+/-12.8 mmHg at 15% hematocrit, but increased again (301+/-33 mmHg) at 11% hematocrit. In contrast, the A-aPO2 difference increased over time in the control group (P < 0.05 between groups over time). Changes in PaO2 in both groups could be explained in large part by variations in intrapulmonary shunt and mixed venous oxygen saturation (SvO2); however, the improvement in gas exchange with hemodilution was not fully explained by significant changes in V(A)/Q or pulmonary blood flow distributions, as quantitated by the coefficient of variation (CV), fractal dimension, and spatial correlation of blood flow. Expired NO increased with with gas embolization but did not change significantly with time or hemodilution.

CONCLUSIONS

Isovolemic hemodilution results in improved oxygen exchange in rabbits with lung injury induced by gas embolization. The mechanism for this improvement is not clear.

Wheat bran decreases aberrant crypt foci, preserves normal proliferation, and increases intraluminal butyrate levels in experimental colon cancer

BACKGROUND

Dietary wheat bran protects against colon cancer, but the mechanism(s) of this effect is not known. Butyrate, produced by colonic bacterial fermentation of dietary polysaccharides, such as wheat bran, induces apoptosis and decreases proliferation in colon cancer cell lines. Whether similar effects occur in vivo is not well defined. We hypothesized that wheat bran's antineoplastic effects in vivo may be mediated in part by butyrate's modulation of apoptosis and proliferation.

METHODS

Male F344 rats were fed wheat bran-supplemented or an isocaloric, isonitrogenous fiber-free diet. Rats were treated with one dose of the carcinogen azoxymethane or vehicle with sacrifice after 5 days (tumor initiation); or two doses (days O and 7) with sacrifice after 56 days (tumor promotion). Study variables included fecal butyrate levels and the intermediate biomarkers of colon carcinogenesis, aberrant crypt foci (ACF), and changes in crypt cell proliferation and apoptosis.

RESULTS

During tumor initiation, wheat bran produced greater apoptosis (p = .01), a trend toward less proliferation, and preserved the normal zone of proliferation (p = .01). At tumor promotion, wheat bran decreased the number of ACF (proximal colon, p = .005; distal colon, p = .047) and maintained the normal proliferative zone. The fiber-free diet shifted the zone of proliferation into the premalignant pattern in both studies. Wheat bran produced significantly higher fecal butyrate (p = .01; .004, .00001) levels than the fiber-free diet throughout the tumor promotion study.

CONCLUSIONS

Wheat bran increased apoptosis and controlled proliferation during tumor initiation and resulted in decreased ACF. Wheat bran's antineoplastic effects occurred early after carcinogen exposure, and were associated with increased fecal butyrate levels.

Mechanisms of improvement in pulmonary gas exchange during isovolemic hemodilution

Severe anemia is associated with remarkable stability of pulmonary gas exchange (S. Deem, M. K. Alberts, M. J. Bishop, A. Bidani, and E. R. Swenson. J. Appl. Physiol. 83: 240-246, 1997), although the factors that contribute to this stability have not been studied in detail. In the present study, 10 Flemish Giant rabbits were anesthetized, paralyzed, and mechanically ventilated at a fixed minute ventilation. Serial hemodilution was performed in five rabbits by simultaneous withdrawal of blood and infusion of an equal volume of 6% hetastarch; five rabbits were followed over a comparable time. Ventilation-perfusion (VA/Q) relationships were studied by using the multiple inert-gas-elimination technique, and pulmonary blood flow distribution was assessed by using fluorescent microspheres. Expired nitric oxide (NO) was measured by chemiluminescence. Hemodilution resulted in a linear fall in hematocrit over time, from 30 +/- 1.6 to 11 +/- 1%. Anemia was associated with an increase in arterial PO(2) in comparison with controls (P < 0.01 between groups). The improvement in O(2) exchange was associated with reduced VA/Q heterogeneity, a reduction in the fractal dimension of pulmonary blood flow (P = 0.04), and a relative increase in the spatial correlation of pulmonary blood flow (P = 0. 04). Expired NO increased with anemia, whereas it remained stable in control animals (P < 0.0001 between groups). Anemia results in improved gas exchange in the normal lung as a result of an improvement in overall VA/Q matching. In turn, this may be a result of favorable changes in pulmonary blood flow distribution, as assessed by the fractal dimension and spatial correlation of blood flow and as a result of increased NO availability.

Endogenous platelet-activating factor is critically involved in effector functions of eosinophils stimulated with IL-5 or IgG

Eosinophil activation and subsequent release of inflammatory mediators are implicated in the pathophysiology of allergic diseases. Eosinophils are activated by various classes of secretagogues, such as cytokines (e.g., IL-5), lipid mediators (e.g., platelet-activating factor (PAF)), and Ig (e.g., immobilized IgG). However, do these agonists act directly on eosinophils or indirectly through the generation of intermediate active metabolites? We now report that endogenous PAF produced by activated eosinophils plays a critical role in eosinophil functions. Human eosinophils produced superoxide when stimulated with immobilized IgG, soluble IL-5, or PAF. Pretreating eosinophils with pertussis toxin abolished their responses to these stimuli, suggesting involvement of a metabolite(s) that acts on G proteins. Indeed, PAF was detected in supernatants from eosinophils stimulated with IgG or IL-5. Furthermore, structurally distinct PAF antagonists, including CV6209, hexanolamine PAF, and Y-24180 (israpafant), inhibited IgG- or IL-5-induced superoxide production and degranulation. Previous reports indicated that exogenous PAF stimulates eosinophil eicosanoid production through formation of lipid bodies. We found in this study that IgG or IL-5 also induces lipid body formation and subsequent leukotriene C4 production mediated by endogenous PAF. Finally, inhibition of cytosolic phospholipase A2, one of the key enzymes involved in PAF synthesis, attenuated both PAF production and effector functions of eosinophils. These findings suggest that endogenous PAF plays important roles in eosinophil functional responses to various exogenous stimuli, such as cytokines and Igs. Therefore, inhibition of PAF synthesis or action may be beneficial for the treatment of eosinophilic inflammation.

Pulmonary embolization causes hypoxemia by redistributing regional blood flow without changing ventilation

To explore mechanisms of hypoxemia after acute pulmonary embolism, we measured regional pulmonary blood flow and alveolar ventilation before and after embolization with 780-micrometers beads in five anesthetized, mechanically ventilated pigs. Regional ventilation and perfusion were determined in approximately 2.0-cm3 lung volumes by using 1-micrometers-diameter aerosolized and 15-micrometers-diameter injected fluorescent microspheres. Hypoxemia after embolization resulted from increased perfusion to regions with low ventilation-to-perfusion ratios. Embolization caused an increase in perfusion heterogeneity and a fall in the correlation between ventilation and perfusion. Correlation between regional ventilation pre- and postembolization was greater than correlation between regional perfusion pre- and postembolization. The majority of regional ventilation-to-perfusion ratio heterogeneity was attributable to changes in regional perfusion. Regional perfusion redistribution without compensatory changes in regional ventilation is responsible for hypoxemia after pulmonary vascular embolization in pigs.

Spatial pattern of pulmonary blood flow distribution is stable over days

Despite the heterogeneous distribution of regional pulmonary perfusion over space, local perfusion remains stable over short time periods (20-100 min). The purpose of this study was to determine whether the spatial distribution of pulmonary perfusion remains stable over longer time periods (1-5 days). Regional blood flow was measured each day for 5 days in five awake standing dogs. Fluorescent microspheres of different colors were injected into a limb vein over 30 s on each day. After the last microsphere injection, the dogs were killed, and lungs were flushed free of blood, excised, dried at total lung capacity, and diced into approximately 2-cm3 pieces (n = 1,296-1,487 per dog). Relative blood flow to each piece on each day was determined by extracting the fluorescent dyes and determining the concentrations of each color. We established that blood flow is spatially heterogeneous with a coefficient of variation of 29.5 +/- 2%. Blood flow to each piece is highly correlated with flow to the same piece on all days (r = 0.930 +/- 0.006). The temporal heterogeneity of regional perfusion as measured by the coefficient of variation is 6.9 +/- 0.7% over the 5 days and is nonrandom. The magnitude of spatial and temporal variation is significantly less than previously reported in a study in which anesthetized and mechanically ventilated dogs were used. We conclude that spatial distribution of pulmonary blood flow remains stable over days and we speculate that in the normal awake dog regional perfusion is determined primarily by a fixed structure such as the geometry of the pulmonary vascular tree rather than by local vasoactive regulators. Anesthesia and/or mechanical ventilation may increase the temporal variability in regional perfusion.

Restraint, dieting, and the continuum model of bulimia nervosa

The authors evaluated the continuity model of bulimia nervosa, which suggests that bulimia results from extreme weight concern and dieting practices. Individuals with bulimia, current dieters, restrained nondieters, and unrestrained nondieters were compared on measures of general psychopathology, eating-disorder-specific psychopathology, and overeating. Multiple methods, including questionnaires, clinical interviews, and food records, were used to collect data. The continuity and discontinuity models were tested with trend and regression analyses. The results of most analyses were consistent with the continuity perspective. However, binge eating behaviour exhibited a clear nonlinear trend, which occurred because binge eating was common in bulimic individuals but virtually non-existent in the other 3 groups. Current dieters scored higher than restrained nondieters on restraint/ weight concern, but not on psychopathology or binge eating. Overall, the results suggest that "normal" dieting is associated with psychological, but not consummatory, symptoms of bulimia.

Restraint, dieting, and the continuum model of bulimia nervosa

The authors evaluated the continuity model of bulimia nervosa, which suggests that bulimia results from extreme weight concern and dieting practices. Individuals with bulimia, current dieters, restrained nondieters, and unrestrained nondieters were compared on measures of general psychopathology, eating-disorder-specific psychopathology, and overeating. Multiple methods, including questionnaires, clinical interviews, and food records, were used to collect data. The continuity and discontinuity models were tested with trend and regression analyses. The results of most analyses were consistent with the continuity perspective. However, binge eating behaviour exhibited a clear nonlinear trend, which occurred because binge eating was common in bulimic individuals but virtually non-existent in the other 3 groups. Current dieters scored higher than restrained nondieters on restraint/ weight concern, but not on psychopathology or binge eating. Overall, the results suggest that "normal" dieting is associated with psychological, but not consummatory, symptoms of bulimia.

Levonorgestrel as a postcoital contraceptive

Time-release pellets of levonorgestrel (LNG), the progestogenic hormone contained in the contraceptive system Norplant, were implanted subdermally in mice, after the animals had mated and ovulated but before uterine implantation of embryos would have occurred, to examine whether the hormone could reduce the number of embryos that subsequently implanted and, if so, when it had to be administered in the postcoital period to achieve that effect. Hybrid female mice (C57BL x CBA) were paired with breeder males (CD-1) and LNG pellets were implanted on day 0, the day on which copulation plugs were found, or on day 2 or day 3 in the postcoital period. Mice in some groups were sacrificed on day 14 of the gestation period, and numbers of fetuses and/or resorption sites were counted, while mice in other groups were allowed to go to term. When LNG pellets were implanted subdermally on day 0 of the postcoital period, pellets designed to release 1.5 mg of hormone in 21 days failed to exhibit a contraceptive effect, but pellets designed to release 5 mg of hormone in 90 days were totally effective in preventing uterine implantation of embryos. Although the 5 mg pellets did not prevent embryos from implanting in all cases when administered on day 2, they prevented pregnancies from going to term by causing resorption of those embryos that did implant. When the pellets were implanted as late as day 3 in the postcoital period, uterine implantation of embryos occurred and fetuses were carried to term. Results of the study indicate that subdermal implants of LNG inserted postcoitally can prevent uterine implantation of embryos in mice, and thereby prevent pregnancy, despite fertilization of oocytes having occurred, if the hormone implants are inserted before day 3 of the postcoital period.

Temporal heterogeneity of regional pulmonary perfusion is spatially clustered

This study investigates temporal changes in regional pulmonary perfusion. Five dogs were studied with five or six different radiolabeled microspheres being injected via a central vein over 30 s every 20 min. The lungs of each animal were cubed into 1.9 cm3 pieces with spatial coordinates noted for each piece. Within individual pieces, the coefficient of variation of regional perfusion over time was 17.2 +/- 6.8% (SD) and across dogs accounted for 7.26 +/- 5.7% of total perfusion heterogeneity. Temporal variability or "twinkling" was not random. When lung pieces with similar temporal flow patterns were grouped together (regardless of spatial location), groups were more tightly clustered in space than expected by chance. Statistical clustering methods revealed regulation of blood flow on a large scale (lobar arteries), and fractal analyses suggested regulation existed on a smaller scale (arterioles). We conclude that regional pulmonary perfusion is heterogeneous over time in a nonrandom pattern and that pieces clustered by temporal patterns of perfusion are neighbors in the spatial domain.

Breast-feeding reduces maternal lower-body fat

The effect of breast-feeding on maternal anthropometric measures during the first 6 postpartum months was studied in 24 women. Mothers, who were seen in the hospital shortly after delivery and at monthly intervals thereafter, kept a record of their infant-feeding practices and provided three 24-hour dietary recalls per month. The women were placed in one of three groups according to their infant-feeding practices: breast-feeding exclusively, combination of breast- and formula-feeding, and formula-feeding only. Changes in anthropometric variables at 6 months postpartum were similar in the three groups, but mothers who breast-fed exclusively or partially had significantly larger reductions in hip circumference measurements (3.6% and 3.1%, respectively) and were less above their prepregnancy weights at 1 month postpartum (7.8% and 8.5% above prepregnancy weight, respectively) than mothers who fed formula exclusively (0.68% reduction in hip circumference and 13.7% above prepregnancy weight). Our findings indicate that a woman's choice of infant-feeding practice influences postpartum anthropometric changes, but these effects may be temporary.

An epizootic of Edwardsiella tarda in largemouth bass (Micropterus salmoides)

Edwardsiella tarda, an opportunistic bacterial pathogen, was isolated from dying largemouth bass (Micropterus salmoides) during an epizootic in a eutrophic lake system, Lochloosa Lake, Florida, USA. Approximately 1,500 adult fish died over a 6-wk period during the late summer and early fall of 1991. A mixed population of aerobic bacteria (E. tarda, Aeromonas hydrophila, and Pseudomonas sp.) was isolated from deep cutaneous ulcers and intestines of moribund bass. However, E. tarda in pure culture was the only bacterium isolated from several viscera of several fish; E. tarda may be the etiologic agent responsible for some episodes of seasonal mortality in largemouth bass.

A comparative study of HLA-DRB1 typing by standard serology and hybridization of non-radioactive sequence-specific oligonucleotide probes to PCR-amplified DNA

A double-blind study was carried out to evaluate the relative performance and reliability of the PCR/SSOP assay compared to conventional serological typing in identifying HLA-DR alleles. A total of 268 consecutive samples were entered into the study. In 14 (5.2%) of the cases, HLA-DR serology could not be performed due to poor cell viability, while in seven (2.6%) of the cases, PCR/SSOP typing could not be performed due to poor amplification or to contamination with exogenous DNA. Among samples that were successfully typed by both methods, serologic typing correctly identified 455/465 (97.9%) DR antigens, while PCR/SSOP correctly identified 464/465 (99.8%) DR alleles (p = 0.0117, McNemar's test). The majority of discrepancies in serologic typing resulted from a lack of discriminative alloantisera to identify DR6 or DR103. For the overall sample set (N = 268), serology provided accurate results in 244 (91.0%) cases, while PCR/SSOP provided accurate results in 260 (97.0%) cases (p = 0.0037). The results of this study demonstrate that PCR/SSOP typing for HLA-DRB1 alleles provides results that are equal to or surpass serological typing for HLA-DR antigens. In addition, the PCR/SSOP approach offers the advantages of better reagent availability, lower cost, more rapid turn-around time, and greater accuracy, all of which would warrant its use as an HLA typing method of choice.