Food constraints explain the restricted distribution of wintering Lesser White‐fronted Geese Anser erythropus in China

More than 90% of the Lesser White‐fronted Geese Anser erythropus in the Eastern Palearctic flyway population winter at East Dongting Lake, China. To explain this restricted distribution and to understand better the winter feeding ecology and habitat requirements of this poorly known species, we assessed their food availability, diet and energy budgets at this site through two winters. Lesser White‐fronted Geese maintained a positive energy budget when feeding on above‐ground green production of Eleocharis and Alopecurus in recessional grasslands in autumn and spring to accumulate fat stores. Such food was severely depleted by late November and showed no growth in mid‐winter. Geese fed on more extensive old‐growth Carex sedge meadows in mid‐winter where they were in energy deficit and depleted endogenous fat stores. Geese failed to accumulate autumn fat stores in one year when high water levels prevented the Geese from using recessional grassland feeding areas. Fat stores remained lower throughout that winter and Geese left for breeding areas later in spring than in the previous year, perhaps reflecting the need to gain threshold fat stores for migration. Sedge meadows are widespread at other Yangtze River floodplain wetlands, but recessional grasslands are rare and perhaps restricted to parts of East Dongting Lake, which would explain the highly localized distribution of Lesser White‐fronted Geese in China and their heavy use of these habitats at this site. Sympathetic management of water tables is essential to maintain the recessional grasslands in the best condition for Geese. Regular depletion of fat stores whilst grazing sedge meadows in mid‐winter also underlines the need to protect the species from unnecessary anthropogenic disturbances that enhance energy expenditure. The specialized diet of the Lesser White‐fronted Goose may explain its highly restricted winter distribution and global rarity.     

Late‐moulting Black‐necked Grebes Podiceps nigricollis show greater body mass in the face of failing food supply

From August to December, thousands of Black‐necked Grebes Podiceps nigricollis concentrate during the flightless moult period in salt ponds in the Odiel Marshes, southern Spain, where they feed on the brine shrimp Artemia parthenogenetica. We predicted that because Black‐necked Grebes moulted in a food‐rich, predator‐free environment, there would be no net loss of body mass caused by the use of fat stored to meet energy needs during remigial feather replacement (as is the case for some other diving waterbirds). However, because the food resource disappears in winter, we predicted that grebes moulting later in the season would put on more body mass prior to moult because of the increasing risk of an Artemia population crash before the moult period is completed. Body mass determinations of thousands of birds captured during 2000–2010 showed that grebes in active wing‐moult showed greater mass with date of capture. Early‐moulting grebes were significantly lighter at all stages than late‐moulting birds. Grebes captured with new feathers post‐moult were significantly lighter than those in moult. This is the first study to support the hypothesis that individual waterbirds adopt different strategies in body mass accumulation according to timing of moult: early‐season grebes were able to acquire an excess of energy over expenditure and accumulate fat stores while moulting. Delayed moulters acquired greater fat stores in advance of moult to contribute to energy expenditure for feather replacement and retained extra stores later, most likely as a bet hedge against the increasing probability of failing food supply and higher thermoregulatory demands late in the season. An alternative hypothesis, that mass change is affected by a trophically transmitted cestode using brine shrimps as an intermediate host and Black‐necked Grebes as final host, was not supported by the data.     

Reversible resistance induced by FLT3 inhibition: a novel resistance mechanism in mutant FLT3-expressing cells

Objectives

Clinical responses achieved with FLT3 kinase inhibitors in acute myeloid leukemia (AML) are typically transient and partial. Thus, there is a need for identification of molecular mechanisms of clinical resistance to these drugs. In response, we characterized MOLM13 AML cell lines made resistant to two structurally-independent FLT3 inhibitors.

Methods

MOLM13 cells were made drug resistant via prolonged exposure to midostaurin and HG-7-85-01, respectively. Cell proliferation was determined by Trypan blue exclusion. Protein expression was assessed by immunoblotting, immunoprecipitation, and flow cytometry. Cycloheximide was used to determine protein half-life. RT-PCR was performed to determine FLT3 mRNA levels, and FISH analysis was performed to determine FLT3 gene expression.

Results and Conclusions

We found that MOLM13 cells readily developed cross-resistance when exposed to either midostaurin or HG-7-85-01. Resistance in both lines was associated with dramatically elevated levels of cell surface FLT3 and elevated levels of phosphor-MAPK, but not phospho-STAT5. The increase in FLT3-ITD expression was at least in part due to reduced turnover of the receptor, with prolonged half-life. Importantly, the drug-resistant phenotype could be rapidly reversed upon withdrawal of either inhibitor. Consistent with this phenotype, no significant evidence of FLT3 gene amplification, kinase domain mutations, or elevated levels of mRNA was observed, suggesting that protein turnover may be part of an auto-regulatory pathway initiated by FLT3 kinase activity. Interestingly, FLT3 inhibitor resistance also correlated with resistance to cytosine arabinoside. Over-expression of FLT3 protein in response to kinase inhibitors may be part of a novel mechanism that could contribute to clinical resistance.     

Selective decrease in paracellular conductance of tight junctions: role of the first extracellular domain of claudin-5

Claudin-5 is a protein component of many endothelial tight junctions, including those at the blood-brain barrier, a barrier that limits molecular exchanges between the central nervous system and the circulatory system. To test the contribution of claudin-5 to this barrier function of tight junctions, we expressed murine claudin-5 in Madin-Darby canine kidney II cells. The result was a fivefold increase in transepithelial resistance in claudin-5 transductants and a reduction in conductance of monovalent cations. However, the paracellular flux of neither neutral nor charged monosaccharides was significantly changed in claudin-5 transductants compared to controls. Therefore, expression of claudin-5 selectively decreased the permeability to ions. Additionally, site-directed mutations of particular amino acid residues in the first extracellular domain of claudin-5 altered the properties of the tight junctions formed in response to claudin-5 expression. In particular, the conserved cysteines were crucial: mutation of either cysteine abolishted the ability of claudin-5 to increase transepithelial resistance, and mutation of Cys(64) strikingly increased the paracellular flux of monosaccharides. These new insights into the functions of claudin-5 at the molecular level in tight junctions may account for some aspects of the blood-brain barrier's selective permeability.     

Sequence-dependent folding of DNA three-way junctions

Three-way DNA junctions can adopt several different conformers, which differ in the coaxial stacking of the arms. These structural variants are often dominated by one conformer, which is determined by the DNA sequence. In this study we have compared several three-way DNA junctions in order to assess how the arrangement of bases around the branch point affects the conformer distribution. The results show that rearranging the different arms, while retaining their base sequences, can affect the conformer distribution. In some instances this generates a structure that appears to contain parallel coaxially stacked helices rather than the usual anti-parallel arrangement. Although the conformer equilibrium can be affected by the order of purines and pyrimidines around the branch point, this is not sufficient to predict the conformer distribution. We find that the folding of three-way junctions can be separated into two groups of dinucleotide steps. These two groups show distinctive stacking properties in B-DNA, suggesting there is a correlation between B-DNA stacking and coaxial stacking in DNA junctions.     

Interactions of T cells with fibroblast-like synoviocytes: role of the B7 family costimulatory ligand B7-H3

Fibroblast-like synoviocytes (FLS) and T cells can activate each other in vitro, and in vivo interactions between these cells may be important in rheumatoid arthritis (RA), yet FLS lack significant expression of CD28 ligands. We sought to identify molecules homologous to CD28 ligands that are strongly expressed by FLS, and documented strong B7-H3 expression on FLS and by fibroblasts of other tissues, which was unaffected by a variety of cytokines. Western blot analysis of FLS lysates showed predominant expression of the larger, four Ig-like domain isoform of B7-H3. Immunohistological sections of RA synovial tissue showed strong staining for B7-H3 on FLS. Cells expressing B7-H3 were distinct from but in close proximity to cells that expressed CD45, CD20, and CD3. Confocal microscopy of FLS and T cell cocultures showed localization of B7-H3 in the region of the T cell-FLS contact point, but distinct from the localization of T cell CD11a/CD18 (LFA-1) and FLS CD54 (ICAM-1). Reduction of B7-H3 expression on FLS by RNA interference affected interactions of FLS with resting T cells or cytokine-activated T cells. Resting T cells showed increased production of TNF-alpha, IFN-gamma, and IL-2, whereas cytokine-activated T cells showed reduced cytokine production relative to control. However, cytokine production by T cells activated through their TCR was not notably altered by knock down of B7-H3. These observations suggest that B7-H3 may be important for the interactions between FLS and T cells in RA, as well as other diseases, and the outcome of such interactions depends on the activation state of the T cell.     

Identification, replication, and fine-mapping of Loci associated with adult height in individuals of african ancestry

Adult height is a classic polygenic trait of high heritability (h ² ∼0.8). More than 180 single nucleotide polymorphisms (SNPs), identified mostly in populations of European descent, are associated with height. These variants convey modest effects and explain ∼10% of the variance in height. Discovery efforts in other populations, while limited, have revealed loci for height not previously implicated in individuals of European ancestry. Here, we performed a meta-analysis of genome-wide association (GWA) results for adult height in 20,427 individuals of African ancestry with replication in up to 16,436 African Americans. We found two novel height loci (Xp22-rs12393627, P = 3.4×10⁻¹² and 2p14-rs4315565, P = 1.2×10⁻⁸). As a group, height associations discovered in European-ancestry samples replicate in individuals of African ancestry (P = 1.7×10⁻⁴ for overall replication). Fine-mapping of the European height loci in African-ancestry individuals showed an enrichment of SNPs that are associated with expression of nearby genes when compared to the index European height SNPs (P<0.01). Our results highlight the utility of genetic studies in non-European populations to understand the etiology of complex human diseases and traits.