The two-headed swan

Pulmonary artery catheterization is a frequent procedure for hemodynamic monitoring in critically ill patients or high-risk surgical patients. Mechanical and infectious complications are recognized, though catheter dysfunction and malposition are more frequent and often require clinical intervention. We present the case of a Swan-Ganz catheter with the appearance of a mechanical fracture at the distal end, which required clinical and radiographic investigation to determine the nature of the aberrancy. The evaluation of a malfunctioning pulmonary artery catheter (PAC) is a frequent occurrence in the intensive care unit and requires careful clinical consideration and radiographic examination.     

Maternal control of vertebrate development before the midblastula transition: mutants from the zebrafish I

Maternal factors control development prior to the activation of the embryonic genome. In vertebrates, little is known about the molecular mechanisms by which maternal factors regulate embryonic development. To understand the processes controlled by maternal factors and identify key genes involved, we embarked on a maternal-effect mutant screen in the zebrafish. We identified 68 maternal-effect mutants. Here we describe 15 mutations in genes controlling processes prior to the midblastula transition, including egg development, blastodisc formation, embryonic polarity, initiation of cell cleavage, and cell division. These mutants exhibit phenotypes not previously observed in zygotic mutant screens. This collection of maternal-effect mutants provides the basis for a molecular genetic analysis of the maternal control of embryogenesis in vertebrates.     

Population genetics and phylogeography of endangered Oxytropis campestris var. chartacea and relatives: arctic-alpine disjuncts in eastern North America

Fassett's locoweed (Oxytropis campestris var. chartacea, Fabaceae) is an endangered perennial endemic to Wisconsin. Patterns of genetic variation within and among six remaining populations and their relationship to other members of the O. campestris complex were analysed using AFLPs from 140 accessions across northern North America. Within-population measures of genetic diversity were high (mean expected heterozygosity HE = 0.16; mean nucleotide diversity pi = 0.015) compared with other herbaceous plants. Estimates of among-population differentiation were low (FST = 0.12; PhiST = 0.29), consistent with outcrossing. Genetic and geographical distances between populations were significantly correlated within Fassett's locoweed (r2 = 0.73, P < 0.002 for Mantel test) and O. campestris as a whole (r2 = 0.63, P < 0.0001). Individual and population-based phylogenetic analyses showed that Fassett's locoweed is monophyletic and sister to O. campestris var. johannensis. Morphometric analyses revealed significant differences between Fassett's locoweed and populations of var. johannensis. The first chromosome count for Fassett's locoweed indicates that it is tetraploid (2n = 32), unlike hexaploid var. johannensis. High within-population diversity and relatively low among-population differentiation are consistent with populations of Fassett's locoweed being relicts of a more continuous Pleistocene distribution. Our data support the continued recognition of Fassett's locoweed and protection under federal and state regulations. High levels of genetic diversity within populations suggest that maintain-ing the ecological conditions that favour the life cycle of this plant may be a more pressing concern than the erosion of genetic variation.     

Proximal airway mucous cells of ovalbumin-sensitized and -challenged Brown Norway rats accumulate the neuropeptide calcitonin gene-related peptide

Mucous cell hypersecretion and increased neuropeptide production play a role in the exacerbation of symptoms associated with asthma. The source of these neuropeptides have been confined to the contributions of small afferent nerves or possibly neuroendocrine cells. We tested the hypothesis that repeated exposure to allergen would alter the sources and abundance of neuropeptides in airways. Right middle lobes from rats (8 wk old) exposed to 2.5% ovalbumin (OVA) for five episodes (30 min each) or filtered air were inflation fixed with paraformaldehyde. The lobes were dissected to expose the airway tree, permeabilized with DMSO, and incubated in antibody to rat calcitonin gene-related peptide (CGRP), followed with a fluorochrome-labeled second antibody. CGRP-positive structures were imaged via confocal microscopy. Airways were later embedded in plastic and sectioned for cell identification. In animals challenged with OVA, CGRP-positive cells, not neuroendocrine or neuronal in origin (confirmed by a lack of protein gene product 9.5 signal), were recorded along the axial path. In section, this fluorescent signal was localized to granules within epithelial cells. Alcian blue/periodic acid-Schiff staining of these same sections positively identify these cells as mucous cells. Mucous cells of animals not challenged with OVA were not positive for CGRP. We conclude that episodic allergen exposure results in the accumulation of CGRP within mucous cells, creating a new source for the release of this neuropeptide within the airway.     

A fungal metallothionein is required for pathogenicity of Magnaporthe grisea

The causal agent of rice blast disease, the ascomycete fungus Magnaporthe grisea, infects rice (Oryza sativa) plants by means of specialized infection structures called appressoria, which are formed on the leaf surface and mechanically rupture the cuticle. We have identified a gene, Magnaporthe metallothionein 1 (MMT1), which is highly expressed throughout growth and development by M. grisea and encodes an unusual 22-amino acid metallothionein-like protein containing only six Cys residues. The MMT1-encoded protein shows a very high affinity for zinc and can act as a powerful antioxidant. Targeted gene disruption of MMT1 produced mutants that show accelerated hyphal growth rates and poor sporulation but had no effect on metal tolerance. Mmt1 mutants are incapable of causing plant disease because of an inability to bring about appressorium-mediated cuticle penetration. Mmt1 appears to be distributed in the inner side of the cell wall of the fungus. These findings indicate that Mmt1-like metallothioneins may play a novel role in fungal cell wall biochemistry that is required for fungal virulence.     

Determination of DNA minor groove width in distamycin-DNA complexes by solid-state NMR

We have performed solid-state ³¹P-¹⁹F REDOR nuclear magnetic resonance (NMR) experiments to monitor changes in minor groove width of the oligonucleotide d(CGCAAA^2′FUTGGC)·d(GCCAAT(pS)TT GCG) (A₃T₂) upon binding of the drug distamycin A at different stoichiometries. In the hydrated solid-state sample, the minor groove width for the unbound DNA, measured as the ^2′FU7–pS19 inter-label distance, was 9.4 ± 0.7 Å, comparable to that found for similar A:T-rich DNAs. Binding of a single drug molecule is observed to cause a 2.4 Å decrease in groove width. Subsequent addition of a second drug molecule results in a larger conformational change, expanding this minor groove width to 13.6 Å, consistent with the results of a previous solution NMR study of the 2:1 complex. These ³¹P-¹⁹F REDOR results demonstrate the ability of solid-state NMR to measure distances of 7–14 Å in DNA–drug complexes and provide the first example of a direct spectroscopic measurement of minor groove width in nucleic acids.     

Associations between mycophagous Drosophila and their Howardula nematode parasites: a worldwide phylogenetic shuffle

Little is known about what determines patterns of host association of horizontally transmitted parasites over evolutionary timescales. We examine the evolution of associations between mushroom-feeding Drosophila flies (Diptera: Drosophilidae), particularly in the quinaria and testacea species groups, and their horizontally transmitted Howardula nematode parasites (Tylenchida: Allantonematidae). Howardula species were identified by molecular characterization of nematodes collected from wild-caught flies. In addition, DNA sequence data is used to infer the phylogenetic relationships of both host Drosophila (mtDNA: COI, II, III) and their Howardula parasites (rDNA: 18S, ITS1; mtDNA: COI). Host and parasite phylogenies are not congruent, with patterns of host association resulting from frequent and sometimes rapid host colonizations. Drosophila-parasitic Howardula are not monophyletic, and host switches have occurred between Drosophila and distantly related mycophagous sphaerocerid flies. There is evidence for some phylogenetic association between parasites and hosts, with some nematode clades associated with certain host lineages. Overall, these host associations are highly dynamic, and appear to be driven by a combination of repeated opportunities for host colonization due to shared breeding sites and large potential host ranges of the nematodes.     

Does female mortality drive male semelparity in dasyurid marsupials?

In some members of the marsupial families Didelphidae and Dasyuridae, males are semelparous, that is, they live for only one mating season. Semelparity is proposed to be the result of the high energy demands of competing for matings with many females during a short breeding season. We argue that high adult female mortality rates between mating and weaning of the offspring selects for a 'bethedging' mating strategy in males. We tested this hypothesis in a well-studied field population of Antechinus agilis by estimating the number of females a male needs to mate with in order to have a high chance of siring at least one offspring that survives to the next breeding season. Our hypothesis predicts that species in which males are semelparous should have higher female mortality rates than species in which males are iteroparous. The limited available data for dasyurid marsupials support this prediction.     

CD28/B7 regulation of anti-CD3-mediated immunosuppression in vivo

FcR-binding "classical" anti-CD3 mAb is a potent immunosuppressive drug that alters CD4(+) and CD8(+) T cell function in vivo via anergy induction and programmed cell death (PCD). Anti-CD3-mediated PCD was Fas independent but was mediated by the mitochondria-initiated apoptosis that was abrogated in Bcl-x(L)-transgenic T cells. The PCD was more pronounced in CD28-deficient mice consistent with defective Bcl-x(L) up-regulation. Residual T cells isolated from anti-CD3-treated wild-type, CD28(-/-), and Bcl-x(L)-transgenic mice were hyporesponsive. The hyporesponsiveness was more pronounced in CD28(-/-) and wild-type mice treated with anti-B7-2, suggesting that CD28 interaction with B7-2 regulates T cell responsiveness in anti-CD3-treated animals. Finally, anti-CD3 treatment led to indefinite cardiac allograft survival in wild-type but not Bcl-x(L) animals. Together these results implicate CD28/B7 signaling in the regulation of both anti-CD3-induced T cell depletion and hyporesponsiveness in vivo, but T cell depletion, not hyporesponsiveness, appears to be critical for anti-CD3 mAb-mediated long-term immune regulation.