How Functional Genomics Can Keep Pace With VUS Identification

Over the last two decades, an exponentially expanding number of genetic variants have been identified associated with inherited cardiac conditions. These tremendous gains also present challenges in deciphering the clinical relevance of unclassified variants or variants of uncertain significance (VUS). This review provides an overview of the advancements (and challenges) in functional and computational approaches to characterize variants and help keep pace with VUS identification related to inherited heart diseases.

Mutation-Specific Differences in Kv7.1 (KCNQ1) and Kv11.1 (KCNH2) Channel Dysfunction and Long QT Syndrome Phenotypes

The electrocardiogram (ECG) empowered clinician scientists to measure the electrical activity of the heart noninvasively to identify arrhythmias and heart disease. Shortly after the standardization of the 12-lead ECG for the diagnosis of heart disease, several families with autosomal recessive (Jervell and Lange-Nielsen Syndrome) and dominant (Romano-Ward Syndrome) forms of long QT syndrome (LQTS) were identified. An abnormally long heart rate-corrected QT-interval was established as a biomarker for the risk of sudden cardiac death. Since then, the International LQTS Registry was established; a phenotypic scoring system to identify LQTS patients was developed; the major genes that associate with typical forms of LQTS were identified; and guidelines for the successful management of patients advanced. In this review, we discuss the molecular and cellular mechanisms for LQTS associated with missense variants in KCNQ1 (LQT1) and KCNH2 (LQT2). We move beyond the "benign" to a "pathogenic" binary classification scheme for different KCNQ1 and KCNH2 missense variants and discuss gene- and mutation-specific differences in K+ channel dysfunction, which can predispose people to distinct clinical phenotypes (e.g., concealed, pleiotropic, severe, etc.). We conclude by discussing the emerging computational structural modeling strategies that will distinguish between dysfunctional subtypes of KCNQ1 and KCNH2 variants, with the goal of realizing a layered precision medicine approach focused on individuals.

Long QT Syndrome KCNH2 Variant Induces hERG1a/1b Subunit Imbalance in Patient-Specific Induced Pluripotent Stem Cell-Derived Cardiomyocytes

[Figure: see text].

The effects of 2-hydroxy-4-methylthio-butanoic acid supplementation on the rumen microbial population and duodenal flow of microbial nitrogen

Four multiparous, lactating Holstein cows (average DIM 169.5 ± 20.5 d), fitted with ruminal and duodenal cannulas, were used in a 4 × 4 Latin square with a 2 × 2 factorial arrangement of treatments to investigate the effects of 2-hydroxy-4-methylthio-butanoic acid (HMTBA) when fed with diets differing in metabolizable protein (MP) supply and equal levels of crude protein on milk production and composition, rumen microbial activity, duodenal protein flow, and rumen bacterial community composition in vivo and in vitro. Experimental periods were 28 d in length. Cows were housed in individual tie stalls and were randomly assigned to 4 dietary treatments: low MP or high MP, supplemented with or without 25 g of HMTBA, which was top-dressed once daily at 0930 h. No interactions were observed between HMTBA and level of dietary MP, with the exception of ruminal acetate-to-propionate ratio. Milk yield was not affected by treatment and averaged 23.8 ± 2.06 kg/d. There was a tendency for increased milk protein percent in cows receiving low MP diets, averaging 3.30 ± 0.09% and 3.21 ± 0.09% for low MP and high MP, respectively. The total-tract apparent digestibility of organic matter, neutral detergent fiber, and nitrogen were greater in cows consuming the low MP diet. Rumen pH was lower in cows consuming high MP diets as well as in those consuming HMTBA. Rumen ammonia concentrations tended to be greater in cows consuming HMTBA, and volatile fatty acid concentrations were greater in cows consuming HMTBA. Duodenal dry matter flow, nitrogen flow, and microbial nitrogen flow did not differ between treatments. The bacterial community structure of cows receiving HMTBA was not affected at the phylum level. The relative abundance of bacterial phyla in vivo differed when compared with in vitro conditions for Firmicutes, Bacteroidetes, Proteobacteria, TM7, Tenericutes, Spirochaetes, SR1, and Verrucomicrobia.

Long QT Syndrome Type 2: Emerging Strategies for Correcting Class 2 KCNH2 (hERG) Mutations and Identifying New Patients

Significant advances in our understanding of the molecular mechanisms that cause congenital long QT syndrome (LQTS) have been made. A wide variety of experimental approaches, including heterologous expression of mutant ion channel proteins and the use of inducible pluripotent stem cell-derived cardiomyocytes (iPSC-CMs) from LQTS patients offer insights into etiology and new therapeutic strategies. This review briefly discusses the major molecular mechanisms underlying LQTS type 2 (LQT2), which is caused by loss-of-function (LOF) mutations in the KCNH2 gene (also known as the human ether-à-go-go-related gene or hERG). Almost half of suspected LQT2-causing mutations are missense mutations, and functional studies suggest that about 90% of these mutations disrupt the intracellular transport, or trafficking, of the KCNH2-encoded Kv11.1 channel protein to the cell surface membrane. In this review, we discuss emerging strategies that improve the trafficking and functional expression of trafficking-deficient LQT2 Kv11.1 channel proteins to the cell surface membrane and how new insights into the structure of the Kv11.1 channel protein will lead to computational approaches that identify which KCNH2 missense variants confer a high-risk for LQT2.

Visualizing Mutation-Specific Differences in the Trafficking-Deficient Phenotype of Kv11.1 Proteins Linked to Long QT Syndrome Type 2

KCNH2 encodes the Kv11.1 α-subunit that underlies the rapidly activating delayed-rectifier K+ current in the heart. Loss-of-function KCNH2 mutations cause long QT syndrome type 2 (LQT2), and most LQT2-linked missense mutations inhibit the trafficking of Kv11.1 channel protein to the cell surface membrane. Several trafficking-deficient LQT2 mutations (e.g., G601S) generate Kv11.1 proteins that are sequestered in a microtubule-dependent quality control (QC) compartment in the transitional endoplasmic reticulum (ER). We tested the hypothesis that the QC mechanisms that regulate LQT2-linked Kv11.1 protein trafficking are mutation-specific. Confocal imaging analyses of HEK293 cells stably expressing the trafficking-deficient LQT2 mutation F805C showed that, unlike G601S-Kv11.1 protein, F805C-Kv11.1 protein was concentrated in several transitional ER subcompartments. The microtubule depolymerizing drug nocodazole differentially affected G601S- and F805C-Kv11.1 protein immunostaining. Nocodazole caused G601S-Kv11.1 protein to distribute into peripheral reticular structures, and it increased the diffuse immunostaining of F805C-Kv11.1 protein around the transitional ER subcompartments. Proteasome inhibition also affected the immunostaining of G601S- and F805C-Kv11.1 protein differently. Incubating cells in MG132 minimally impacted G601S-Kv11.1 immunostaining, but it dramatically increased the diffuse immunostaining of F805C-Kv11.1 protein in the transitional ER. Similar results were seen after incubating cells in the proteasome inhibitor lactacystin. Differences in the cellular distribution of G601S-Kv11.1 and F805C-Kv11.1 protein persisted in transfected human inducible pluripotent stem cell derived cardiomyocytes. These are the first data to visually demonstrate mutation-specific differences in the trafficking-deficient LQT2 phenotype, and this study has identified a novel way to categorize trafficking-deficient LQT2 mutations based on differences in intracellular retention.

Functional Invalidation of Putative Sudden Infant Death Syndrome-Associated Variants in the KCNH2-Encoded Kv11.1 Channel

BACKGROUND

Heterologous functional validation studies of putative long-QT syndrome subtype 2-associated variants clarify their pathological potential and identify disease mechanism(s) for most variants studied. The purpose of this study is to clarify the pathological potential for rare nonsynonymous KCNH2 variants seemingly associated with sudden infant death syndrome.

METHODS

Genetic testing of 292 sudden infant death syndrome cases identified 9 KCNH2 variants: E90K, R181Q, A190T, G294V, R791W, P967L, R1005W, R1047L, and Q1068R. Previous studies show R181Q-, P967L-, and R1047L-Kv11.1 channels function similar to wild-type Kv11.1 channels, whereas Q1068R-Kv11.1 channels accelerate inactivation gating. We studied the biochemical and biophysical properties for E90K-, G294V-, R791W-, and R1005W-Kv11.1 channels expressed in human embryonic kidney 293 cells; examined the electronic health records of patients who were genotype positive for the sudden infant death syndrome-linked KCNH2 variants; and simulated their functional impact using computational models of the human ventricular action potential.

RESULTS

Western blot and voltage-clamping analyses of cells expressing E90K-, G294V-, R791W-, and R1005W-Kv11.1 channels demonstrated these variants express and generate peak Kv11.1 current levels similar to cells expressing wild-type-Kv11.1 channels, but R791W- and R1005W-Kv11.1 channels accelerated deactivation and activation gating, respectively. Electronic health records of patients with the sudden infant death syndrome-linked KCNH2 variants showed that the patients had median heart rate-corrected QT intervals <480 ms and none had been diagnosed with long-QT syndrome or experienced cardiac arrest. Simulating the impact of dysfunctional gating variants predicted that they have little impact on ventricular action potential duration.

CONCLUSIONS

We conclude that these rare Kv11.1 missense variants are not long-QT syndrome subtype 2-causative variants and therefore do not represent the pathogenic substrate for sudden infant death syndrome in the variant-positive infants.

Abstract 394: Multiple Cellular Mechanisms Underlie the Trafficking-deficient Phenotype for Kv11.1 (hERG) Mutations Linked to Long QT Syndrome

Type 2 Long QT syndrome (LQT2) is commonly caused by missense mutations that disrupt the trafficking of Kv11.1 channels. The goal of this study is to determine the cellular mechanisms that underlie the trafficking-deficient phenotype for LQT2-linked mutations located in different channel domains. We expressed the pore-domain mutation G601S and the cyclic nucleotide binding domain mutation F805C in human embryonic kidney 293 (HEK293) cells or human inducible pluripotent stem cell derived cardiomyocytes (hiPSC-CMs). HEK293 cells or hiPSC-CMs expressing G601S showed a diffuse intracellular anti-Kv11.1 staining pattern that colocalized with the transitional endoplasmic reticulum (ER) marker BAP31, but not markers for the rough ER (calnexin), ER-associated degradation compartment (derlin1), ER exit sites (Sec31), or the ER-Golgi intermediate compartment (ERGIC53). Culturing cells in the drug E-4031 (10 μM, 24 hrs), which corrects the G601s trafficking-deficient phenotype, decreased its colocalization with BAP31. Unlike G601S, the trafficking-deficient phenotype for F805C is not corrected by culturing cells in E-4031. Expressing F805C in HEK293 cells or hiPSC-CMs showed a very different anti-Kv11.1 staining pattern that consisted of several discrete aggregates. In hiPSC-CMs, the F805C aggregates partially overlapped with derlin1 staining and co-transfected green fluorescent protein (gfp) in the cytosol. Incubating cells in the proteasome inhibitor bortezomib (10 μM, 4 hrs) dispersed the F805C aggregates to generate a diffuse intracellular staining pattern. We conclude that G601S and F805C localize to distinct ER subcompartments: G601S is sequestered in the transitional ER and F805C localizes to an ER associated degradation subcompartment that is sensitive to proteasome inhibition.

Rumen bacterial communities can be acclimated faster to high concentrate diets than currently implemented feedlot programs

Aims

Recent studies have demonstrated RAMP^®, a complete starter feed, to have beneficial effects for animal performance. However, how RAMP may elicit such responses is unknown. To understand if RAMP adaptation results in changes in the rumen bacterial community that can potentially affect animal performance, we investigated the dynamics of rumen bacterial community composition in corn‐adapted and RAMP‐adapted cattle.

Methods and Results

During gradual acclimation of the rumen bacterial communities, we compared the bacterial community dynamics in corn and RAMP‐adapted using 16S rRNA gene amplicon sequencing. Significant shifts in bacterial populations across diets were identified. The shift in corn‐adapted animals occurred between adaptation step3 and step4, whereas in RAMP‐adapted cattle, the shift occurred between step2 and step3. As the adaptation program progressed, the abundance of OTUs associated with family Prevotellaceae and S24‐7 changed in corn‐adapted animals. In RAMP‐adapted animals, OTUs belonging to family Ruminococcaceae and Lachnospiraceae changed in abundance.

Conclusions

Rumen bacteria can be acclimated faster to high concentrate diets, such as RAMP, than traditional adaptation programs and the speed of bacterial community acclimation depends on substrate composition.

Significance and Impact of the Study

These findings may have implications for beef producers to reduce feedlot costs, as less time adapting animals would result in lower feed costs. However, animal feeding behavior patterns and other factors must be considered.

Molecular pathogenesis of long QT syndrome type 2

The molecular mechanisms underlying congenital long QT syndrome (LQTS) are now beginning to be understood. New insights into the etiology and therapeutic strategies are emerging from heterologous expression studies of LQTS-linked mutant proteins, as well as inducible pluripotent stem cell derived cardiomyocytes (iPSC-CMs) from LQTS patients. This review focuses on the major molecular mechanism that underlies LQTS type 2 (LQT2). LQT2 is caused by loss of function (LOF) mutations in KCNH2 (also known as the human Ether-à-go-go-Related Gene or hERG). Most LQT2-linked mutations are missense mutations and functional studies suggest that ~90% of them disrupt the intracellular transport (trafficking) of KCNH2-encoded Kv11.1 proteins to the cell membrane. Trafficking deficient LQT2 mutations disrupt Kv11.1 protein folding and misfolded Kv11.1 proteins are retained in the endoplasmic reticulum (ER) until they are degraded in the ER associated degradation pathway (ERAD). This review focuses on the quality control mechanisms in the ER that contribute to the folding and ERAD of Kv11.1 proteins; the mechanism for ER export of Kv11.1 proteins in the secretory pathway; different subclasses of trafficking deficient LQT2 mutations; and strategies being developed to mitigate or correct trafficking deficient LQT2-related phenotypes.

Mouse ERG K(+) channel clones reveal differences in protein trafficking and function

Background

The mouse ether‐a‐go‐go‐related gene 1a (mERG1a, mKCNH2) encodes mERG K⁺ channels in mouse cardiomyocytes. The mERG channels and their human analogue, hERG channels, conduct I_Kr. Mutations in hERG channels reduce I_Kr to cause congenital long‐QT syndrome type 2, mostly by decreasing surface membrane expression of trafficking‐deficient channels. Three cDNA sequences were originally reported for mERG channels that differ by 1 to 4 amino acid residues (mERG‐London, mERG‐Waterston, and mERG‐Nie). We characterized these mERG channels to test the postulation that they would differ in their protein trafficking and biophysical function, based on previous findings in long‐QT syndrome type 2.

Methods and Results

The 3 mERG and hERG channels were expressed in HEK293 cells and neonatal mouse cardiomyocytes and were studied using Western blot and whole‐cell patch clamp. We then compared our findings with the recent sequencing results in the Welcome Trust Sanger Institute Mouse Genomes Project (WTSIMGP).

Conclusions

First, the mERG‐London channel with amino acid substitutions in regions of highly ordered structure is trafficking deficient and undergoes temperature‐dependent and pharmacological correction of its trafficking deficiency. Second, the voltage dependence of channel gating would be different for the 3 mERG channels. Third, compared with the WTSIMGP data set, the mERG‐Nie clone is likely to represent the wild‐type mouse sequence and physiology. Fourth, the WTSIMGP analysis suggests that substrain‐specific sequence differences in mERG are a common finding in mice. These findings with mERG channels support previous findings with hERG channel structure–function analyses in long‐QT syndrome type 2, in which sequence changes in regions of highly ordered structure are likely to result in abnormal protein trafficking.

Pharmacological correction of long QT-linked mutations in KCNH2 (hERG) increases the trafficking of Kv11.1 channels stored in the transitional endoplasmic reticulum

KCNH2 encodes Kv11.1 and underlies the rapidly activating delayed rectifier K(+) current (IKr) in the heart. Loss-of-function KCNH2 mutations cause the type 2 long QT syndrome (LQT2), and most LQT2-linked missense mutations inhibit the trafficking of Kv11.1 channels. Drugs that bind to Kv11.1 and block IKr (e.g., E-4031) can act as pharmacological chaperones to increase the trafficking and functional expression for most LQT2 channels (pharmacological correction). We previously showed that LQT2 channels are selectively stored in a microtubule-dependent compartment within the endoplasmic reticulum (ER). We tested the hypothesis that pharmacological correction promotes the trafficking of LQT2 channels stored in this compartment. Confocal analyses of cells expressing the trafficking-deficient LQT2 channel G601S showed that the microtubule-dependent ER compartment is the transitional ER. Experiments with E-4031 and the protein synthesis inhibitor cycloheximide suggested that pharmacological correction promotes the trafficking of G601S stored in this compartment. Treating cells in E-4031 or ranolazine (a drug that blocks IKr and has a short half-life) for 30 min was sufficient to cause pharmacological correction. Moreover, the increased functional expression of G601S persisted 4-5 h after drug washout. Coexpression studies with a dominant-negative form of Rab11B, a small GTPase that regulates Kv11.1 trafficking, prevented the pharmacological correction of G601S trafficking from the transitional ER. These data suggest that pharmacological correction quickly increases the trafficking of LQT2 channels stored in the transitional ER via a Rab11B-dependent pathway, and we conclude that the pharmacological chaperone activity of drugs like ranolazine might have therapeutic potential.

Amazonia through time: Andean uplift, climate change, landscape evolution, and biodiversity

The Amazonian rainforest is arguably the most species-rich terrestrial ecosystem in the world, yet the timing of the origin and evolutionary causes of this diversity are a matter of debate. We review the geologic and phylogenetic evidence from Amazonia and compare it with uplift records from the Andes. This uplift and its effect on regional climate fundamentally changed the Amazonian landscape by reconfiguring drainage patterns and creating a vast influx of sediments into the basin. On this "Andean" substrate, a region-wide edaphic mosaic developed that became extremely rich in species, particularly in Western Amazonia. We show that Andean uplift was crucial for the evolution of Amazonian landscapes and ecosystems, and that current biodiversity patterns are rooted deep in the pre-Quaternary.

The expression of caveolin-1 and the distribution of caveolae in the murine placenta and yolk sac: parallels to the human placenta

The expression pattern of caveolin-1 and the distribution of caveolae in the murine placental labyrinth and visceral yolk sac have been determined. Immunoblot analysis demonstrates that both placenta and yolk sac express the protein caveolin-1. Immunofluorescence microscopy was used to determine which cell types in the placental labyrinth and yolk sac express caveolin-1. In yolk sac, detectable caveolin-1 was restricted to endothelial cells and smooth muscle cells of the vitelline vasculature and to mesothelial cells. Endoderm, the major cell type in the yolk sac, does not express caveolin-1 as assessed by this assay. In the labyrinth region of the placenta, endothelial cells express caveolin-1 but this protein was not detectable in any of the three trophoblast layers. These tissues were also examined by electron microscopy to determine which cell types contain the specialized plasma membrane microdomains known as caveolae. Morphologically detectable caveolae were present in endothelial and smooth muscle cells, as well as mesothelial cells of the yolk sac and in endothelial cells of the placental labyrinth. Neither endodermal cells of the yolk sac nor trophoblastic cells in the placental labyrinth contained caveolae-like structures. We conclude that caveolin-1 and caveolae have restricted distribution in the murine placenta and yolk sac and that this parallels the situation in human placenta.

Cell-free complements in vivo expression of the E. coli membrane proteome

Reconstituted cell-free (CF) protein expression systems hold the promise of overcoming the traditional barriers associated with in vivo systems. This is particularly true for membrane proteins, which are often cytotoxic and due to the nature of the membrane, difficult to work with. To evaluate the potential of cell-free expression, we cloned 120 membrane proteins from E. coli and compared their expression profiles in both an E. coli in vivo system and an E. coli-derived cell-free system. Our results indicate CF is a more robust system and we were able to express 63% of the targets in CF, compared to 44% in vivo. To benchmark the quality of CF produced protein, five target membrane proteins were purified and their homogeneity assayed by gel filtration chromatography. Finally, to demonstrate the ease of amino acid labeling with CF, a novel membrane protein was substituted with selenomethionine, purified, and shown to have 100% incorporation of the unnatural amino acid. We conclude that CF is a novel, robust expression system capable of expressing more proteins than an in vivo system and suitable for production of membrane proteins at the milligram level.

Drug-induced long QT syndrome: hERG K+ channel block and disruption of protein trafficking by fluoxetine and norfluoxetine

BACKGROUND AND PURPOSE

Fluoxetine (Prozac) is a widely prescribed drug in adults and children, and it has an active metabolite, norfluoxetine, with a prolonged elimination time. Although uncommon, Prozac causes QT interval prolongation and arrhythmias; a patient who took an overdose of Prozac exhibited a prolonged QT interval (QTc 625 msec). We looked for possible mechanisms underlying this clinical finding by analysing the effects of fluoxetine and norfluoxetine on ion channels in vitro.

EXPERIMENTAL APPROACH

We studied the effects of fluoxetine and norfluoxetine on the electrophysiology and cellular trafficking of hERG K+ and SCN5A Na+ channels heterologously expressed in HEK293 cells.

KEY RESULTS

Voltage clamp analyses employing square pulse or ventricular action potential waveform protocols showed that fluoxetine and norfluoxetine caused direct, concentration-dependent, block of hERG current (IhERG). Biochemical studies showed that both compounds also caused concentration-dependent reductions in the trafficking of hERG channel protein into the cell surface membrane. Fluoxetine had no effect on SCN5A channel or HEK293 cell endogenous current. Mutations in the hERG channel drug binding domain reduced fluoxetine block of IhERG but did not alter fluoxetine's effect on hERG channel protein trafficking.

CONCLUSIONS AND IMPLICATIONS

Our findings show that both fluoxetine and norfluoxetine at similar concentrations selectively reduce IhERG by two mechanisms, (1) direct channel block, and (2) indirectly by disrupting channel protein trafficking. These two effects are not mediated by a single drug binding site. Our findings add complexity to understanding the mechanisms that cause drug-induced long QT syndrome.

Most LQT2 mutations reduce Kv11.1 (hERG) current by a class 2 (trafficking-deficient) mechanism

BACKGROUND

The KCNH2 or human ether-a-go-go related gene (hERG) encodes the Kv11.1 alpha-subunit of the rapidly activating delayed rectifier K+ current (IKr) in the heart. Type 2 congenital long-QT syndrome (LQT2) results from KCNH2 mutations that cause loss of Kv11.1 channel function. Several mechanisms have been identified, including disruption of Kv11.1 channel synthesis (class 1), protein trafficking (class 2), gating (class 3), or permeation (class 4). For a few class 2 LQT2-Kv11.1 channels, it is possible to increase surface membrane expression of Kv11.1 current (IKv11.1). We tested the hypotheses that (1) most LQT2 missense mutations generate trafficking-deficient Kv11.1 channels, and (2) their trafficking-deficient phenotype can be corrected.

METHODS AND RESULTS

Wild-type (WT)-Kv11.1 channels and 34 missense LQT2-Kv11.1 channels were expressed in HEK293 cells. With Western blot analyses, 28 LQT2-Kv11.1 channels had a trafficking-deficient (class 2) phenotype. For the majority of these mutations, the class 2 phenotype could be corrected when cells were incubated for 24 hours at reduced temperature (27 degrees C) or in the drugs E4031 or thapsigargin. Four of the 6 LQT2-Kv11.1 channels that had a wild-type-like trafficking phenotype did not cause loss of Kv11.1 function, which suggests that these channels are uncommon sequence variants.

CONCLUSIONS

This is the first study to identify a dominant mechanism, class 2, for the loss of Kv11.1 channel function in LQT2 and to report that the class 2 phenotype for many of these mutant channels can be corrected. This suggests that if therapeutic strategies to correct protein trafficking abnormalities can be developed, it may offer clinical benefits for LQT2 patients.

Specific serine proteases selectively damage KCNH2 (hERG1) potassium channels and I(Kr)

KCNH2 (hERG1) encodes the alpha-subunit proteins for the rapidly activating delayed rectifier K+ current (I(Kr)), a major K+ current for cardiac myocyte repolarization. In isolated myocytes I(Kr) frequently is small in amplitude or absent, yet KCNH2 channels and I(Kr) are targets for drug block or mutations to cause long QT syndrome. We hypothesized that KCNH2 channels and I(Kr) are uniquely sensitive to enzymatic damage. To test this hypothesis, we studied heterologously expressed K+, Na+, and L-type Ca2+ channels, and in ventricular myocytes I(Kr), slowly activating delayed rectifier K+ current (I(Ks)), and inward rectifier K+ current (I(K1)), by using electrophysiological and biochemical methods. 1) Specific exogenous serine proteases (protease XIV, XXIV, or proteinase K) selectively degraded KCNH2 current (I(KCNH2)) and its mature channel protein without damaging cell integrity and with minimal effects on the other channel currents; 2) immature KCNH2 channel protein remained intact; 3) smaller molecular mass KCNH2 degradation products appeared; 4) protease XXIV selectively abolished I(Kr); and 5) reculturing HEK-293 cells after protease exposure resulted in the gradual recovery of I(KCNH2) and its mature channel protein over several hours. Thus the channel protein for I(KCNH2) and I(Kr) is uniquely sensitive to proteolysis. Analysis of the degradation products suggests selective proteolysis within the S5-pore extracellular linker, which is structurally unique among Kv channels. These data provide 1) a new mechanism to account for low I(Kr) density in some isolated myocytes, 2) evidence that most complexly glycosylated KCNH2 channel protein is in the plasma membrane, and 3) new insight into the rate of biogenesis of KCNH2 channel protein within cells.

Intragenic suppression of trafficking-defective KCNH2 channels associated with long QT syndrome

Mutations in the KCNH2 or human ether-a-go-go-related gene-encoded K(+) channel reduce functional KCNH2 current (I(KCNH2)) to cause long QT syndrome (LQT2) by multiple mechanisms, including defects in intracellular transport (trafficking). Trafficking-deficient, or class 2, LQT2 mutations reduce the Golgi processing and surface membrane expression of KCNH2 channel proteins. Drugs that associate with pore-S6 intracellular drug binding domain of KCNH2 channel proteins to cause high-affinity block of I(KCNH2) also can increase the processing of class 2 LQT2 channel proteins through the secretory pathway. We used a strategy of intragenic suppression to test the hypothesis that amino acid substitutions in the putative drug binding domain at residue Y652 could compensate for protein folding abnormalities caused by class 2 LQT2 mutations. We found that the Y652C substitution, and to lesser extent the Y652S substitution, resulted in intragenic suppression of the class 2 LQT2 G601S phenotype; these substitutions increased Golgi processing of G601S channel proteins. The Y652C substitution also caused intragenic suppression of the class 2 LQT2 V612L and F640V phenotypes but not the LQT2 N470D or F805C phenotypes. These are the first findings to demonstrate that a single amino acid substitution in the putative KCNH2 drug binding domain can cause intragenic suppression of several LQT2 mutations.

The dynamics of X-inactivation skewing as women age

Non-random X-chromosome inactivation (XCI) has been associated with X-linked diseases, neoplastic diseases, recurrent pregnancy loss, and trisomy risk. It also occurs more commonly in older female populations. To understand the etiology of non-random XCI and utilize this assay appropriately in clinical research and practice, the age-related alteration in XCI patterns in normal females needs to be clearly defined. In the present study, we evaluated the XCI status in 350 unselected women aged 0-88 years with unknown history of genetic disorders or abnormal pregnancies. DNA samples were extracted from peripheral blood and analyzed by a methylation-based assay at the androgen receptor locus. A weak but significant positive correlation was observed between age and degree of skewing in XCI over the whole age range (r = 0.23, p < 0.0001), and skewing values become non-normally distributed at older ages. However, the increase in skewed XCI appears to be more pronounced after age 30 than at younger ages. This trend supports the model of increased skewing with age as a consequence of hematopoietic stem cell senescence. An alternative possibility is that there is allele-specific loss of methylation with time that results in the appearance of increased XCI skewing using a methylation-based assay.

Pharmacological rescue of trafficking defective HERG channels formed by coassembly of wild-type and long QT mutant N470D subunits

Mutations in the human ether-a-go-go-related gene (HERG) cause long QT syndrome. We previously showed that the HERG N470D mutation expressed as homotetrameric channels causes a protein trafficking defect, and this can be corrected by the HERG channel blocking drug E-4031. The N470D mutant also has been reported to cause dominant negative suppression of HERG current when coexpressed with wild-type channel subunits. The aims of this study were 1). to investigate the molecular mechanism responsible for the dominant negative effect of the N470D mutant coexpressed with wild-type subunits and 2). to test whether the trafficking defective heteromeric channels could be pharmacologically rescued by E-4031. Using a combination of immunoprecipitation and Western blot methods, we showed that N470D mutant and wild-type HERG subunits were physically associated in the endoplasmic reticulum as heteromeric channels. The coassembly resulted in the retention of both wild-type and N470D subunits in the endoplasmic reticulum. Culturing cells in E-4031 increased the cell surface expression of these channels, although with an altered electrophysiological phenotype. These results suggest that the dominant negative effect of the N470D wild-type coassembled channels is caused by retention of heteromeric channels in the endoplasmic reticulum and that the trafficking defect of these channels can be corrected by specific pharmacological strategies.

Molecular and functional characterization of common polymorphisms in HERG (KCNH2) potassium channels

Long QT syndrome (LQTS) is a cardiac repolarization disorder that can lead to arrhythmias and sudden death. Chromosome 7-linked inherited LQTS (LQT2) is caused by mutations in human ether-a-go-go-related gene (HERG; KCNH2), whereas drug-induced LQTS is caused primarily by HERG channel block. Many common polymorphisms are functionally silent and have been traditionally regarded as benign and without physiological consequence. However, the identification of common nonsynonymous single nucleotide polymorphisms (nSNPs; i.e., amino-acid coding variants) with functional phenotypes in the SCN5A Na(+) channel and MiRP1 K(+) channel beta-subunit have challenged this viewpoint. In this report, we test the hypothesis that common missense HERG polymorphisms alter channel physiology. Comprehensive mutational analysis of HERG was performed on genomic DNA derived from a population-based cohort of sudden infant death syndrome and two reference allele cohorts derived from 100 African American and 100 Caucasian individuals. Amino acid-encoding variants were considered common polymorphisms if they were present in at least two of the three study cohorts with an allelic frequency >0.5%. Four nSNPs were identified: K897T, P967L, R1047L, and Q1068R. Wild-type (WT) and polymorphic channels were heterologously expressed in human embryonic kidney cells, and biochemical and voltage-clamp techniques were used to characterize their functional properties. All channel types were processed similarly, but several electrophysiological differences were identified: 1) K897T current density was lower than the other polymorphic channels; 2) K897T channels activated at more negative potentials than WT and R1047L; 3) K897T and Q1068R channels inactivated and recovered from inactivation faster than WT, P967L, and R1047L channels; and 4) K897T channels showed subtle differences compared with WT channels when stimulated with an action potential waveform. In contrast to K897T and Q1068R channels, P967L and R1047L channels were electrophysiologically indistinguishable from WT channels. All HERG channels had similar sensitivity to block by cisapride. Therefore, some HERG polymorphic channels are electrophysiologically different from WT channels.

Thapsigargin selectively rescues the trafficking defective LQT2 channels G601S and F805C

Several mutations in the human ether-a-go-go-related K+ channel gene (HERG or KCNH2) cause long QT syndrome (LQT2) by reducing the intracellular transport (trafficking) of the channel protein to the cell surface. Drugs that bind to and block HERG channels (i.e. E4031) rescue the surface expression of some trafficking defective LQT2 mutations. Because these drugs potently block HERG current, their ability to correct congenital LQT is confounded by their risk of causing acquired LQT. We tested the hypothesis that pharmacological rescue can occur without HERG channel block. Thapsigargin (1 microM), a sarcoplasmic/endoplasmic reticulum Ca2+-ATPase inhibitor, rescued the surface expression of G601S, and it did so without blocking current. Thapsigargin-induced rescue and E4031-induced rescue caused complex glycosylation that was evident within 3 h of drug exposure. Disruption of the Golgi apparatus with brefeldin A prevented thapsigargin- and E4031-induced rescue of IG01S. Confocal imaging showed that G601S protein is predominantly "trapped" intracellularly and that both thapsigargin and E4031 promote its relocation to the surface membrane. We also studied two other trafficking defective LQT2 mutations. Thapsigargin rescued the C terminus mutation F805C but not N470D, whereas E4031 rescued N470D but not F805C. Other sarcoplasmic/endoplasmic reticulum Ca2+-ATPase inhibitors did not rescue G601S or F805C. This study 1) supports the hypothesis that the LQT2 trafficking defective phenotype can be reversed without blocking the channel; 2) demonstrates pharmacological rescue of a C terminus LQT2 mutation; and 3) shows that thapsigargin can correct trafficking defective phenotypes in more than one channel type and disease (i.e. LQT2 and cystic fibrosis).

An empirical analysis of mt 16S rRNA covarion-like evolution in insects: site-specific rate variation is clustered and frequently detected

The structural and functional analysis of rRNA molecules has attracted considerable scientific interest. Empirical studies have demonstrated that sequence variation is not directly translated into modifications of rRNA secondary structure. Obviously, the maintenance of secondary structure and sequence variation are in part governed by different selection regimes. The nature of those selection regimes still remains quite elusive. The analysis of individual bacterial models cannot adequately explore this topic. Therefore, we used primary sequence data and secondary structures of a mitochondrial 16S rRNA fragment of 558 insect species from 15 monophyletic groups to study patterns of sequence variation, and variation of secondary structure. Using simulation studies to establish significance levels of change, we found that despite conservation of secondary structure, the location of sequence variation within the conserved rRNA structure changes significantly between groups of insects. Despite our conservative estimation procedure we found significant site-specific rate changes at 56 sites out of 184. Additionally, site-specific rate variation is somewhat clustered in certain helices. Both results confirm what has been predicted from an application of non-stationary maximum likelihood models to rRNA sequences. Clearly, constraints on sequence variation evolve and leave footprints in the form of evolutionary plasticity in rRNA sequences. Here, we show that a better understanding of the evolution of rRNA sequences can be obtained by integrating both phylogenetic and structural information.

Exposure-based death rates for child motor vehicle occupants

We used reports of additional occupants on trips from the Nationwide Personal Transportation Survey to estimate travel in cars and trucks for children age nine years and younger. For children age five to nine years these indirect estimates were 98% of directly reported travel. Using this travel data, the death rate was 4.0 per billion km of travel for children less than age one year and decreased to 1.7 for children age nine years. Infants have a higher exposure-based death rate for travel in cars and trucks than older children despite greater restraint use.

Role of glycosylation in cell surface expression and stability of HERG potassium channels

The human ether-à-go-go-related gene (HERG) encodes the pore-forming subunit of the rapidly activating delayed rectifier potassium channel in the heart. We previously showed that HERG channel protein is modified by N-linked glycosylation. HERG protein sequence contains two extracellular consensus sites for N-linked glycosylation (N598, N629). In this study, we used the approaches of site-directed mutagenesis and biochemical modification to inhibit N-linked glycosylation and studied the role of glycosylation in the cell surface expression and turnover of HERG channels. Our results show that N598 is the only site for N-linked glycosylation and that glycosylation is not required for the cell surface expression of functional HERG channels. In contrast, N629 is not used for glycosylation, but mutation of this site (N629Q) causes a protein trafficking defect, which results in its intracellular retention. Pulse-chase experiments show that the turnover rate of nonglycosylated HERG channel is faster than that of the glycosylated form, suggesting that N-linked glycosylation plays an important role in HERG channel stability.

Pharmacological rescue of human K(+) channel long-QT2 mutations: human ether-a-go-go-related gene rescue without block

BACKGROUND

Defective protein trafficking is a consequence of gene mutations. Human long-QT (LQT) syndrome results from mutations in several genes, including the human ether-a-go-go-related gene (HERG), which encodes a delayed rectifier K(+) current. Trafficking-defective mutant HERG protein is a mechanism for reduced delayed rectifier K(+) current in LQT2, and high-affinity HERG channel-blocking drugs can result in pharmacological rescue. Methods and Results- We postulated that drug molecules modified to remove high-affinity HERG block may still stabilize mutant proteins in a conformation required for rescue. We tested terfenadine carboxylate (fexofenadine) and terfenadine, structurally similar drugs with markedly different affinities for HERG block, for rescue of trafficking-defective LQT2 mutations. Terfenadine rescued the N470D mutation but blocked the channels. In contrast, fexofenadine rescued N470D with a half-maximal rescue concentration of 177 nmol/L, which is approximately 350-fold lower than the half-maximal channel block concentration. The G601S mutation was also rescued without channel block.

CONCLUSIONS

Pharmacological rescue can occur without channel block. This could represent a new antiarrhythmic paradigm in the treatment of some trafficking-defective LQT2 mutations.

Pickup truck use in the National Personal Transportation Survey

To guide interventions to prevent injuries to pickup-truck occupants, we characterized pickup truck ownership, drivers and use in the 1995 National Personal Transportation Survey, which collects travel data from the civilian noninstitutionalized population of the US. SUDAAN software was used to account for the complex nature of the sample. Pickup truck ownership was more common in households with more vehicles, in rural households, in households living in single family homes and mobile homes, and in middle-income households. Among US regions, pickup truck ownership was highest among households in the mountain west. Pickup truck ownership was greater in households with two adults, whether or not children or youths were present, but this was largely due to the number of vehicles in these households. Driving a pickup on the sample day was more frequent among men, among drivers with less education and among full-time workers. A higher proportion of trips to work, work-related trips, longer trips and trips with fewer people were by pickup truck. Seat belt use was lower among pickup truck drivers than drivers of other vehicles. For only 0.5% of households (those with three or more members and a pickup truck as their only vehicle), restrictions on travel in cargo areas might be burdensome. Restrictions on cargo area travel, strengthening existing seat belt laws and social marketing strategies might increase the safety of pickup truck occupants.

Patterns of occurrence and 18S rDNA sequence variation of PKX (Tetracapsula bryosalmonae), the causative agent of salmonid proliferative kidney disease

Recent progress in understanding the etiology of proliferative kidney disease (PKD) includes the identification of freshwater bryozoans as the natural hosts of the myxozoan parasite that causes the disease in salmonid fish and formal description of the parasite as Tetracapsula bryosalmonae. This paper presents data on patterns of occurrence of T. bryosalmonae and sequence variation among isolates. T. bryosalmonae infects bryozoans that range from primitive to more derived genera within the Phylactolaemata and that differ in growth form and habits. Infected bryozoans have been collected in diverse habitats including cold, clear streams and warm, eutrophic lakes. Temporal surveys reveal intra- and interannual variation in infection levels, and spatial variation in incidence of infection is implicit by the apparent absence of T. bryosalmonae from many bryozoan populations. The significance of minor variation in partial sequences of 18S rDNA requires further investigation. The information presented here provides the first significant insights into the ecology of T. bryosalmonae.

Injury in children of low-income Mexican, Mexican American, and non-Hispanic white mothers in the USA: a focused ethnography

Several studies indicate that rates of serious pediatric injury are higher among Hispanics than among non-Hispanic whites in the USA. To investigate possible contributory factors, we interviewed 50 Mexican, 30 Mexican American, and 30 non-Hispanic white mothers in their own homes in the same low-income neighborhoods of Southern California. Mothers were identified via door-to-door canvassing in areas with high rates of pediatric injury. We observed household conditions and behaviors and obtained a detailed family history, including accounts of any occurrence of serious injury in a child under 5 years old, the highest-risk age group for pediatric injury. Results show that Mexican families were poorer, less educated, and lived in more hazardous and crowded conditions than did families in the other two groups. Nevertheless, they benefited from strong family bonds and a cultural tradition in which responsible older children typically supervise younger siblings. In contrast, a number of Mexican American and white mothers had been abused as children and were estranged from their own mothers; hence they lacked support and models of good parenting. There was much less self-reported smoking, drug use, and mental dysfunction among the Mexican mothers and their male partners as well as much less excessively active and/or aggressive behavior among their children. The nature of the injuries reported by the various groups seemed to reflect these differences. Appropriate interventions for each group are discussed. The study illustrates the importance of using ethnographic methods to examine the context of pediatric injury at the household level.

The Fc receptor for IgG expressed in the villus endothelium of human placenta is Fc gamma RIIb2

To evaluate the potential role of human placental endothelial cells in the transport of IgG from maternal to fetal circulation, we studied Fc gamma receptor (Fc gamma R) expression by immunohistology and immunoblotting. Several pan-Fc gamma RII Abs that label the placental endothelium displayed a distribution pattern that correlated well with transport functions, being intense in the terminal villus and nil in the cord. In contrast, the MHC class 1-like IgG transporter, FcRn, and the classical Fc gamma RIIa were not expressed in transport-related endothelium of the placenta. Our inference, that Fc gamma RIIb was the likely receptor, we confirmed by analyzing purified placental villi, enriched in endothelium, by immunoblotting with a new Ab specific for the cytoplasmic tail of Fc gamma RIIb. These experiments showed that the Fc gamma RII expressed in villus endothelium was the b2 isoform whose cytoplasmic tail is known to include a phosphotyrosyl-based motif that inhibits a variety of immune responses. We suggest that this receptor is perfectly positioned to transport IgG although as well it may scavenge immune complexes.

Localization of FCGR1 encoding Fcgamma receptor class I in primates: molecular evidence for two pericentric inversions during the evolution of human chromosome 1

The human high-affinity receptor for immunoglobulin G, FcgammaRI (FCGR1), is encoded by a family of three genes that share over 95% sequence homology. Curiously, the three genes in this recently duplicated gene family flank the centromere of human chromosome 1, with FCGR1B located at 1p12 and both FCGR1A and FCGR1C located at 1q21. We have previously speculated that a pericentric inversion could account for the separation of the genes in the FCGR1 family and explain their current chromosomal location. Here we present evidence, obtained through fluorescence in situ hybridization analysis, that in the rhesus monkey (Macaca mulatta) and baboon (Papio papio) FCGR1 is located adjacent to the centromere on the chromosomal arm with greatest homology to human 1p, whereas in the chimpanzee (Pan troglodytes) it is located adjacent to the centromere on the chromosomal arm with greatest homology to human 1q. The separation of the FCGR1 gene family in humans suggests that the location of a second pericentric inversion, known to distinguish the human from the chimpanzee chromosome 1, is within the FCGR1 gene family. This finding refines the assignment of homology between the human and chimpanzee chromosomes 1.

The adapter protein LAT enhances fcgamma receptor-mediated signal transduction in myeloid cells

FcgammaR clustering in monocytes initiates a cascade of signaling events that culminate in biological responses such as phagocytosis, production of inflammatory cytokines, and generation of reactive oxygen species. We have identified and determined the function of the adapter protein linker of activation of T cell (LAT) in FcgammaR-mediated signaling and function. Clustering of FcgammaRs on the human monocytic cell line, THP-1, induces phosphorylation of a major 36-kDa protein which immunoreacts with anti-LAT antisera. Our data indicate that although both the 36-kDa and 38-kDa isoforms of LAT are expressed in THP-1 and U937 human monocytic cells, FcgammaR clustering induces phosphorylation of the 36-kDa isoform only. Co-immunoprecipitation experiments revealed a constitutive association of p36 LAT with both FcgammaRI and FcgammaRIIa immunoprecipitates, and an activation-induced association of LAT with PLCgamma1, Grb2, and the p85 subunit of phosphatidylinositol 3-kinase. Transient transfection experiments in COS-7 cells indicated that overexpression of a wild type but not a dominant-negative LAT, that is incapable of binding to p85, enhances phagocytosis by FcgammaRI. Furthermore, bone marrow-derived macrophages from LAT-deficient mice displayed reduced phagocytic efficiency in comparison to the macrophages from wild-type mice. Thus, we conclude that p36 LAT serves to enhance FcgammaR-induced signal transduction in myeloid cells.

Fatalities to occupants of cargo areas of pickup trucks

We sought to describe the fatalities to occupants of pickup truck cargo areas and to compare the mortality of cargo area occupants to passengers in the cab. From the Fatality Analysis Reporting System (FARS) files for 1987-1996, we identified occupants of pickup trucks with at least one fatality and at least one passenger in the cargo area. Outcomes of cargo area occupants and passengers in the cab were compared using estimating equations conditional on the crash and vehicle. Thirty-four percent of deaths to cargo occupants were in noncrash events without vehicle deformation. Fifty-five percent of those who died were age 15-29 years and 79% were male. The fatality risk ratio (FRR) comparing cargo area occupants to front seat occupants was 3.0 (95% Confidence Interval [CI] = 2.7-3.4). The risk was 7.9 (95% CI = 6.2-10.1) times that of restrained front seat occupants. The FRR ranged from 92 (95% CI = 47-179) in noncrash events to 1.7 (95% CI = 1.5-1.9) in crashes with severe vehicle deformation. The FRR was 1.8 (95% CI = 1.4-2.3) for occupants of enclosed cargo areas and 3.5 (95% CI = 3.1-4.0) for occupants of open cargo areas. We conclude that passengers in cargo areas of pickup trucks have a higher risk of death than front seat occupants, especially in noncrash events, and that camper shells offer only limited protection for cargo area occupants.

Childhood sexual abuse history and role reversal in parenting

OBJECTIVE

This study explored the main and interactive effects of sexual abuse history and relationship satisfaction on self-reported parenting, controlling for histories of physical abuse and parental alcoholism.

METHOD

The community sample consisted of 90 mothers of 5- to 8-year-old children. The sample was limited to those mothers currently in an intimate relationship, 19 of whom reported a history of childhood sexual abuse. Participants completed the Child Behavior Checklist, the Parenting Stress Inventory, the Family Cohesion Index, and questions assessing parent-child role reversal, history of abuse and parental alcoholism, and current relationship satisfaction.

RESULTS

Results of analyses and multivariate analyses of covariance suggested that sexual abuse survivors with an unsatisfactory intimate relationship were more likely than either sexual abuse survivors with a satisfactory relationship or nonabused women to endorse items on a questionnaire of role reversal (defined as emotional overdependence upon one's child). Role reversal was not significantly predicted by histories of physical abuse or parental alcoholism or child's gender. While parenting stress was inversely predicted by the significant main effect of relationship satisfaction, neither parenting stress nor child behavior problems were predicted by the main effect of sexual abuse history or by the interaction between sexual abuse history and relationship satisfaction.

CONCLUSIONS

These results suggest the unique relevance of sexual abuse history and relationship satisfaction in the prediction of a specific type of parent-child role reversal--namely, a mother's emotional overdependence upon her child.

A phylogeny of the damselfly genus calopteryx (Odonata) using mitochondrial 16S rDNA markers

We seek to reconstruct the phylogenetic relationships of the damselfly genus Calopteryx, for which extensive behavioral and morphological knowledge already exists. To date, analyses of the evolutionary pathways of different life history traits have been hampered by the absence of a robust phylogeny based on morphological data. In this study, we concentrate on establishing phylogenetic information from parts of the 16S rDNA gene, which we sequenced for nine Calopteryx species and five outgroup species. The mt 16S rDNA data set did not show signs of saturated variation for ingroup taxa, and phylogenetic reconstructions were insensitive to variation of outgroup taxa. Parsimony, neighbor-joining, and maximum-likelihood reconstructions agreed on parts of the tree. A consensus tree summarizes the significant results and indicates problematic nodes. The 16S rDNA sequences support monophyly of the genera Mnais, Matrona, and Calopteryx. However, the genus Calopteryx may not be monophyletic, since Matrona basilaris and Calopteryx atrata are sister taxa under every parameter setting. The North American and European taxa each appear as monophyletic clades, while the Asian Calopteryx atrata and Calopteryx cornelia are not monophyletic. Our data implies a different paleobiogeographic history of the Eurasian and North American species, with extant Eurasian species complexes shaped by glacial periods, in contrast to extant North American species groups.

Zinc has no effect on IL-3-mediated apoptosis of BAF-3 cells but enhances CD95-mediated apoptosis of jurkat cells

The feasibility of using a zinc-inducible gene expression system for the study of apoptosis-controlling genes in BAF-3 murine B cells and Jurkat human T cells was evaluated. Initially, cell sensitivity to a range of zinc concentrations was examined. It was found that zinc concentrations above 60 microM were toxic to BAF-3 cells and those above 50 microM were toxic to Jurkat cells. Secondly, the zinc concentration required to achieve maximal gene expression was examined. BAF-3 cells transiently transfected with the pMTCB6+/luciferase vector were exposed to zinc concentrations ranging from 0-120 microM, whilst stably transfected Jurkat cells were exposed to 0-70 microM zinc. At zinc concentrations nontoxic to each cell type, the maximum induction achieved was 20-fold (at 60 microM) in BAF-3 cells, and 7.5-fold (at 50 microM) in Jurkat cells. Thirdly, the effect of zinc on apoptosis was examined. It was shown that exposure to nontoxic zinc concentrations had no effect on IL-3 withdrawal-mediated apoptosis of BAF-3 cells. However, in the case of Jurkat cells, pre-exposure to zinc augmented CD95-mediated apoptosis. These results illustrate the importance of characterizing individual cell lines when using zinc-inducible gene expression systems.

Analysis of fatalities in extended cab pickup trucks using an estimating equation method

We compared the fatality risk for occupants of rear passenger seats in extended cab and crew cab pickup trucks to the fatality risk for front seat occupants of the same vehicles using the (US) Fatality Analysis Reporting System (FARS) for 1982-1997. A 10-digit truncated vehicle identification number was used to classify the pickup trucks. The data were analyzed with an estimating equation for data having few observations per stratum. We identified 549 extended cab pickup trucks with one or more occupants of rear passenger seats and one or more occupant deaths. Occupants of rear passenger seats had a fatality risk 43% lower than front seat occupants (95% confidence interval 32% to 52%), controlling for age, sex, and restraint use. Occupants of rear seats of extended cabs in compact pickup trucks did not experience any higher fatality risk (relative to front-seat occupants of the same vehicles) than rear seat occupants of extended cabs in full-size pickup trucks and large 4-door crew cabs.

Physiological determinants of performance on an indoor military obstacle course test

Obstacle courses (OCs), physical challenge courses, and confidence courses are valuable in training and assessing military troops. However, OCs are not well characterized with regard to physical demands and requisite abilities. The purpose of this study was to evaluate the physical capabilities associated with success on an OC. Male subjects (N = 47) were assessed on an OC, skinfolds, upper and lower body aerobic and anaerobic power, muscular strength, and endurance. Faster performers were lighter (p < 0.003), leaner, and, relative to body weight, averaged greater arm anaerobic peak and mean power, leg aerobic power, one-repetition maximum leg press, and one-repetition maximum latissimus dorsi pull-down, than slower performers. There were significant correlations between OC time and weight (0.59), percent fat (0.54), anaerobic leg mean power (-0.43), arm anaerobic peak (-0.48) and mean power (-0.48), and arm (-0.51) and leg aerobic power (-0.53), all expressed relative to body weight. A three-variable regression model accounted for 35% of the variation in OC time. Good performers on this OC displayed many diverse physical capabilities.

Molecular data implicate bryozoans as hosts for PKX (phylum Myxozoa) and identify a clade of bryozoan parasites within the Myxozoa

Proliferative kidney disease (PKD), a condition associated with high mortality in salmonid fish, represents an abnormal immune response to the presence of an enigmatic myxozoan, which has been designated simply as PKX organism because its generic and specific status are obscure. Phylogenetic analyses of partial sequences of the 18S rDNA of PKX and of myxozoan parasites infecting the bryozoans Cristatella mucedo, Pectinatella magnifica and Plumatella rugosa, including the previously named Tetracapsula bryozoides from C. mucedo, showed that these taxa represent a distinct clade that diverged early in the evolution of the Myxozoa before the radiation of the other known myxozoan genera. A common feature of the myxozoans in this clade may be the electron-dense sporoplasmosomes with a lucent bar-like structure, which occur in T. bryozoides and PKX but not in the myxozoans belonging to the established orders Bivalvulida and Multivalvulida. Variation of 0.5-1.1% was found among the PKX 18S rDNA sequences obtained from fish from North America and Europe. The 18S rDNA sequence for T. bryozoides showed that it is a distinct taxon, not closely related to PKX but some sequences from myxozoans infecting 2 of the bryozoan species were so similar to those of PKX as to be indistinguishable. Other sequences from the new myxozoans in bryozoans at first appeared distinct from PKX in a maximum likelihood tree but, when analysed further, were also found to be phylogenetically indistinguishable from PKX. We propose that at least some variants of these new myxozoans from bryozoans are able to infect and multiply in salmonid fish, in which they stimulate the immune reaction and cause PKD but are unable to form mature spores to complete their development.

Ultrastructure of Myxidium trachinorum sp. nov. from the gallbladder of the lesser weever fish Echiichthys vipera

Myxidium trachinorum sp. nov. is described from the gallbladder of the lesser weever fish Echiichthys vipera. Pseudoplasmodia attach themselves to the gallbladder epithelium by filose processes, which are inserted between host cells. Pseudoplasmodia undergo endogenous cell formation at the secondary and tertiary levels. In the proliferative cycle, primary and endogenous cells are packed with digestive vacuoles formed by phagocytosis. In the sporogonic cycle the pseudoplasmodium becomes a pericyte enclosing two secondary cells (lacking digestive vacuoles) in a vacuole. These give rise to five cells each two valvogenic, two capsulogenic and a binucleate sporoplasm, which mature into spores. Comparison of the disporic M. trachinorum with polysporic species of Myxidium revealed significant differences in plasmodial ultrastructure, especially their attachments to host cells, surface characteristics and mode of nutrition, and in formation of generative cells. These suggest that the genus Myxidium may require revision.

Polymorphic X-chromosome inactivation of the human TIMP1 gene

X inactivation silences most but not all of the genes on one of the two X chromosomes in mammalian females. The human X chromosome preserves its activation status when isolated in rodent/human somatic-cell hybrids, and hybrids retaining either the active or inactive X chromosome have been used to assess the inactivation status of many X-linked genes. Surprisingly, the X-linked gene for human tissue inhibitor of metalloproteinases (TIMP1) is expressed in some but not all inactive X-containing somatic-cell hybrids, suggesting that this gene is either prone to reactivation or variable in its inactivation. Since many genes that escape X inactivation are clustered, we examined the expression of four genes (ARAF1, ELK1, ZNF41, and ZNF157) within approximately 100 kb of TIMP1. All four genes were expressed only from the active X chromosome, demonstrating that the factors allowing TIMP1 expression from the inactive X chromosome are specific to the TIMP1 gene. To determine if this variable inactivation of TIMP1 is a function of the hybrid-cell environment or also is observed in human cells, we developed an allele-specific assay to assess TIMP1 expression in human females. Expression of two alleles was detected in some female cells with previously demonstrated extreme skewing of X inactivation, indicating TIMP1 expression from the inactive chromosome. However, in other cells, no expression of TIMP1 was observed from the inactive X chromosome, suggesting that TIMP1 inactivation is polymorphic in human females.

Household poisoning exposure among children of Mexican-born mothers: an ethnographic study

OBJECTIVE

To explore reasons for high rates of unintentional poisoning among Latino children under 5 years old.

DESIGN

Ethnographic interviews were carried out using a sample of mothers identified via door-to-door canvassing in an area with documented high injury rates among Latino children. Interviews included many open-ended and follow-up questions to elicit a detailed family history and emphasized observation of conditions and behaviors in the homes.

SETTING

Low-income neighborhoods of Southern California.

SUBJECTS

Fifty mothers born in Mexico with children under 5 years old.

RESULTS

Children were exposed to potential poisoning agents in more than 80% of homes. Contributory factors related to culture included favorable attitudes toward iron as a healthful substance; extensive use of products that lack child-resistant packaging, such as rubbing alcohol and medicines from Mexico; high prevalence of shared housing; limited familiarity with toxic household chemicals not widely used in Mexico; and inability to read warning labels in English.

CONCLUSION

Current Poison Control Center outreach efforts should be expanded. Clinicians are uniquely positioned to advise parents about the safe use and storage of toxic substances, including widely used products lacking child-resistant packaging. Medicines should be labeled in Spanish for those who do not know English.

The SH2-containing 5'-inositol phosphatase (SHIP) is tyrosine phosphorylated after Fc gamma receptor clustering in monocytes

Current models of Fc gamma R signal transduction in monocytes describe a molecular cascade that begins upon clustering of Fc gamma R with the phosphorylation of critical tyrosine residues in the cytoplasmic domains of Fc gamma RIIa or the gamma-chain subunit of Fc gamma RI and Fc gamma RIIIa. The cascade engages several other tyrosine-phosphorylated molecules, either enzymes or adapters, to manifest ultimately an array of biological responses, including phagocytosis, cell killing, secretion of a variety of inflammatory mediators, and activation. Continuing to assess systematically the molecules participating in the cascade, we have found that the SH2-containing 5'-inositol phosphatase (SHIP) is phosphorylated on tyrosine early and transiently after Fc gamma R clustering. This molecule in other systems, such as B cells and mast cells, mediates an inhibitory signal. We find that clustering of either Fc gamma RIIa or Fc gamma RI is effective in inducing SHIP phosphorylation, that SHIP binds in vitro to a phosphorylated immunoreceptor tyrosine-based activation motif, peptide from the cytoplasmic domain of Fc gamma RIIa in activation-independent fashion, although SHIP binding increases upon cell activation, and that Fc gamma RIIb and Fc gamma RIIc are not responsible for the observed SHIP phosphorylation. These findings prompt us to propose that SHIP inhibits Fc gamma R-mediated signal transduction by engaging immunoreceptor tyrosine-based activation motif-containing cytoplasmic domains of Fc gamma RIIa and Fc gamma RI-associated gamma-chain.