Developmentally Arrested Precursors of Pontine Neurons Establish an Embryonic Blueprint of the Drosophila Central Complex

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Firefly luciferase luminescence assays using scintillation counters for quantitation in transfected mammalian cells

The firefly enzyme luciferase catalyzes the luminescent reaction of luciferin with ATP and oxygen. The luciferase gene has recently been cloned and proposed as a reporter gene in procaryotic and eucaryotic cells. We present here a luciferase activity assay which relies on luminescence detection using a standard scintillation counter. This technique is simple, fast, inexpensive, and still very sensitive: as little as 0.02 pg (250,000 molecules) of enzyme is readily detected. The technique is optimized for the luciferase assay in mammalian cell lysates. Thus, the luciferase gene may become a very useful tool for gene regulation studies.     

Characterization of the heparin binding sites in human apolipoprotein E

Apolipoprotein (apo) E mediates lipoprotein remnant clearance via interaction with cell-surface heparan sulfate proteoglycans. Both the 22-kDa N-terminal domain and 10-kDa C-terminal domain of apoE contain a heparin binding site; the N-terminal site overlaps with the low density lipoprotein receptor binding region and the C-terminal site is undefined. To understand the molecular details of the apoE-heparin interaction, we defined the microenvironments of all 12 lysine residues in intact apoE3 and examined their relative contributions to heparin binding. Nuclear magnetic resonance measurements showed that, in apoE3-dimyristoyl phosphatidylcholine discs, Lys-143 and -146 in the N-terminal domain and Lys-233 in the C-terminal domain have unusually low pK(a) values, indicating high positive electrostatic potential around these residues. Binding experiments using heparin-Sepharose gel demonstrated that the lipid-free 10-kDa fragment interacted strongly with heparin and a point mutation K233Q largely abolished the binding, indicating that Lys-233 is involved in heparin binding and that an unusually basic lysine microenvironment is critical for the interaction with heparin. With lipidated apoE3, it is confirmed that the Lys-233 site is completely masked and the N-terminal site mediates heparin binding. In addition, mutations of the two heparin binding sites in intact apoE3 demonstrated the dominant role of the N-terminal site in the heparin binding of apoE even in the lipid-free state. These results suggest that apoE interacts predominately with cell-surface heparan sulfate proteoglycans through the N-terminal binding site. However, Lys-233 may be involved in the binding of apoE to certain cell-surface sites, such as the protein core of biglycan.     

Quantifying and Understanding Voltage Losses Due to Nonradiative Recombination in Bulk Heterojunction Organic Solar Cells with Low Energetic Offsets

Open‐circuit voltage (V_OC) losses in organic photovoltaics (OPVs) inhibit devices from reaching V_OC values comparable to the bandgap of the donor–acceptor blend. Specifically, nonradiative recombination losses (?V_nr) are much greater in OPVs than in silicon or perovskite solar cells, yet the origins of this are not fully understood. To understand what makes a system have high or low loss, an investigation of the nonradiative recombination losses in a total of nine blend systems is carried out. An apparent relationship is observed between the relative domain purity of six blends and the degree of nonradiative recombination loss, where films exhibiting relatively less pure domains show lower ?V_nr than films with higher domain purity. Additionally, it is shown that when paired with a fullerene acceptor, polymer donors which have bulky backbone units to inhibit close π–π stacking exhibit lower nonradiative recombination losses than in blends where the polymer can pack more closely. This work reports a strategy that ensures ?V_nr can be measured accurately and reports key observations on the relationship between ?V_nr and properties of the donor/acceptor interface.     

Heme catabolism in the causative agent of anthrax

A challenge common to all bacterial pathogens is to acquire nutrients from hostile host environments. Iron is an important cofactor required for essential cellular processes such as DNA repair, energy production and redox balance. Within a mammalian host, most iron is sequestered within heme, which in turn is predominantly bound by hemoglobin. While little is understood about the mechanisms by which bacterial hemophores attain heme from host‐hemoglobin, even less is known about intracellular heme processing. Bacillus anthracis, the causative agent of anthrax, displays a remarkable ability to grow in mammalian hosts. Hypothesizing this pathogen harbors robust ways to catabolize heme, we characterize two new intracellular heme‐binding proteins that are distinct from the previously described IsdG heme monooxygenase. The first of these, HmoA, binds and degrades heme, is necessary for heme detoxification and facilitates growth on heme iron sources. The second protein, HmoB, binds and degrades heme too, but is not necessary for heme utilization or virulence. The loss of both HmoA and IsdG renders B. anthracis incapable of causing anthrax disease. The additional loss of HmoB in this background increases clearance of bacilli in lungs, which is consistent with this protein being important for survival in alveolar macrophages.     

Extrafloral nectar increases seed removal by ants in Turnera ulmifolia

To investigate whether extrafloral nectar (EFN) increases seed dispersal in Turnera ulmifolia, we measured seed removal on plants with and without EFN. Plants producing EFN had more seeds removed than control plants, suggesting that EFN does play a role in seed dispersal. This is a novel function of EFN.     

Connective Auxin Transport in the Shoot Facilitates Communication between Shoot Apices

The bulk polar movement of the plant signaling molecule auxin through the stem is a long-recognized but poorly understood phenomenon. Here we show that the highly polar, high conductance polar auxin transport stream (PATS) is only part of a multimodal auxin transport network in the stem. The dynamics of auxin movement through stems are inconsistent with a single polar transport regime and instead suggest widespread low conductance, less polar auxin transport in the stem, which we term connective auxin transport (CAT). The bidirectional movement of auxin between the PATS and the surrounding tissues, mediated by CAT, can explain the complex auxin transport kinetics we observe. We show that the auxin efflux carriers PIN3, PIN4, and PIN7 are major contributors to this auxin transport connectivity and that their activity is important for communication between shoot apices in the regulation of shoot branching. We propose that the PATS provides a long-range, consolidated stream of information throughout the plant, while CAT acts locally, allowing tissues to modulate and be modulated by information in the PATS.     

Lysyl Hydroxylase 3 Localizes to Epidermal Basement Membrane and Is Reduced in Patients with Recessive Dystrophic Epidermolysis Bullosa

Recessive dystrophic epidermolysis bullosa (RDEB) is caused by mutations in COL7A1 resulting in reduced or absent type VII collagen, aberrant anchoring fibril formation and subsequent dermal-epidermal fragility. Here, we identify a significant decrease in PLOD3 expression and its encoded protein, the collagen modifying enzyme lysyl hydroxylase 3 (LH3), in RDEB. We show abundant LH3 localising to the basement membrane in normal skin which is severely depleted in RDEB patient skin. We demonstrate expression is in-part regulated by endogenous type VII collagen and that, in agreement with previous studies, even small reductions in LH3 expression lead to significantly less secreted LH3 protein. Exogenous type VII collagen did not alter LH3 expression in cultured RDEB keratinocytes and we show that RDEB patients receiving bone marrow transplantation who demonstrate significant increase in type VII collagen do not show increased levels of LH3 at the basement membrane. Our data report a direct link between LH3 and endogenous type VII collagen expression concluding that reduction of LH3 at the basement membrane in patients with RDEB will likely have significant implications for disease progression and therapeutic intervention.