Cell surface proteoglycans syndecan-1 and -4 bind overlapping but distinct sites in laminin α3 LG45 protein domain

Keratinocyte migration during epidermal repair depends on interactions between cellular heparan sulfate proteoglycan receptors, syndecan-1 and -4, and the C-terminal globular domains (LG45) of the extracellular matrix protein laminin 332. This study investigates the molecular basis of the binding specificity of the syndecan-1 and -4 receptors expressed by human keratinocytes. We used site-directed mutagenesis to alter a recombinant LG45 protein by substituting the most critical basic residues with glutamine. All proteins were expressed in mammalian cells, purified, and characterized biochemically. We used in vitro binding assays, including surface plasmon resonance, to examine interactions between mutated LG45 and heparan sulfates, syndecan-1 and -4. We identify a major heparin binding domain on the outer edge of a β-strand of LG45 surrounded by a track of converging low affinity residues. This domain harbors distinctive syndecan-1 and -4 binding-specific sequences. This is the first study to demonstrate a binding specificity of two proteoglycans produced by a single cell type. In addition, we found that although syndecan-1 interacts exclusively through its glycosaminoglycan chains, syndecan-4 binding relies on both its core protein and its heparan sulfate chains. These results suggest that LG45 may trigger different signals toward keratinocytes depending on its interaction with syndecan-1 or -4.     

Temporal partitioning among diurnally and nocturnally active desert spiny mice: energy and water turnover costs

Nocturnal Acomys cahirinus and diurnally active A. russatus coexist in hot rocky deserts. Diurnal and nocturnal activity exposes them to different climatic challenges. A doubly-labelled water field study revealed no significant differences in water turnover between the species at all seasons, reflecting the adaptations of A. russatus to water conservation. In summers the energy expenditure of A. russatus tended to be higher than that of A. cahirinus. Energy requirements of A. cahirinus in winter are double than that of A. russatus, and may reflect the cost of thermoregulating during cold nights.     

Light masking in the field: an experiment with nocturnal and diurnal spiny mice under semi-natural field conditions

Light masking has been studied almost exclusively in the laboratory. The authors populated four field enclosures with locally coexisting nocturnal Acomys cahirinus and diurnal A. russatus, and monitored their body temperatures (T(b)) using implanted temperature-sensitive radio transmitters. A 3-h light pulse was initiated at the beginning of two consecutive nights; preceding nights were controls. A. cahirinus T(b) and calculated activity levels decreased significantly during the light pulse, demonstrating a negative light masking response (light effect on T(b): -0.32 °C?±?0.15 °C; average calculated activity records during the light pulse: 7?±?1.53, control: 9.8?±?1.62). Diurnal A. russatus did not respond to the light pulse. We conclude that light masking is not an artifact of laboratory conditions but represents a natural adaptive response in free-living populations.     

Adaptive thermoregulation in golden spiny mice: the influence of season and food availability on body temperature

We studied the effect of food supplementation during summer and winter in seminatural field conditions on thermoregulation of a desert rodent, the golden spiny mouse Acomys russatus. We hypothesized that (a) under natural food availability (control conditions), mice will use less precise thermoregulation (i.e., an increase in the variance of body temperature [T(b)]) during winter because of low ambient temperatures (T(a)'s) and low food availability and during summer because of low food and water availability; (b) food supplementation will result in more precise thermoregulation during winter, but the effect will be smaller during summer because variation in T(b) in summer is also driven by water availability during that period. We found that under natural food availability, spiny mice thermoregulated more precisely during summer than during winter. They spent more time torpid during summer than during winter even when food was supplemented (although summer nights are shorter), allowing them to conserve water. Supplementing food resulted in more precise thermoregulation in both seasons, and mice spent less time torpid. In summer, thermoregulation at high T(a)'s was less precise, resulting in higher maximum T(b)'s in summer than in winter and when food was supplemented, in accord with the expected effect of water shortage on thermoregulation. Our results suggest that as expected, precise thermoregulation is beneficial when possible and is abandoned only when the costs of homeothermy outweigh the benefits.     

Expression and anatomical distribution of TIM-containing molecules in Langerhans cell sarcoma

Signals from the T cell immunoglobulin and mucin-domain (TIM)-containing molecules have been demonstrated to be involved in regulating the progress of carcinoma. However, the expression and anatomical distribution of TIMs in Langerhans cell sarcoma (LCS), which is a rare malignancy derived from dendritic cells of the epidermis, has yet to be determined. In this study, the expression of TIM-1, TIM-3 and TIM-4 in LCS samples were detected by immunohistochemistry. Our results showed that these three molecules were found in LCS sections. At the cellular level, these molecules were found on the cell membrane and in the cytoplasm. Immunofluorescence double-staining demonstrated that these TIMs were co-expressed with Langerin, a potential biomarker for detecting LCS. In addition, TIM-1 was also expressed on CD68⁺ macrophages and CK-18⁺ epithelial cells, while TIM-3 and TIM-4 were expressed on all cell types investigated, including CD3⁺T cells, CD68⁺ macrophages, CD11c⁺ dendritic cells, CD16⁺ NK Cells, CD31⁺ endothelial cells and CK-18⁺ epithelial cells. Interestingly, TIMs were also co-expressed with some members of the B7 superfamily, including B7-H1, B7-H3 and B7-H4 on sarcoma cells. Our results clearly showed the characteristic expression and anatomical distribution of TIMs in LCS, and a clear understanding of their functional roles may further elucidate the pathogenesis of this carcinoma and potentially contribute to the development of novel immunotherapeutic strategies.     

Identifying Three Ecological Chemotypes of Xanthium strumarium Glandular Trichomes Using a Combined NMR and LC-MS Method

Xanthanolides, as the sesquiterpene lactones, are reportedly the major components for the pharmacological properties of X. strumarium L. species. Phytochemical studies indicated that the glandular structures on the surface of plant tissues would form the primary sites for the accumulation of this class of the compounds. As the interface between plants and their natural enemies, glandular trichomes may vary with respect to which of their chemicals are sequestered against different herbivores in different ecologies. However, to date, no data are available on the chemical characterisation of X. strumarium glandular cells. In this study, the trichome secretions of the X. strumarium species originating from nineteen unique areas across eleven provinces in China, were analysed by HPLC, LC-ESI-MS and NMR. For the first time three distinct chemotypes of X. strumarium glandular trichomes were discovered along with the qualitative and quantitative evaluations of their presence of xanthanolides; these were designated glandular cell Types I, II, and III, respectively. The main xanthanolides in Type I cells were 8-epi-xanthatin and xanthumin while no xanthatin was detected. Xanthatin, 8-epi-xanthatin, and xanthumin dominated in Type II cells with comparable levels of each being present. For Type III cells, significantly higher concentrations of 8-epi-xanthatin or xanthinosin (relative to xanthatin) were detected with xanthinosin only being observed in this type. Further research will focus on understanding the ecological and molecular mechanism causing these chemotype differences in X. strumarium glandular structures.     

Community-wide character displacement in the presence of clines: a test of Holarctic weasel guilds

1. Competition is thought to be a major influence on community assembly, ecology and evolution; presence of competitors may cause divergence in traits related to resource use (character displacement). 2. Such traits, however, often vary clinally, and this phenomenon may be independent of the presence or absence of competing species. 3. The presence of such clines can either obscure the effects of competition, or create an impression that competition is operating when, in fact, it is not. 4. We corrected for clinal variation while testing for character displacement in two well-studied weasel (Mustela) guilds, in the Nearctic and the west Palaearctic. 5. Without accounting for clines, our results agreed with previous studies suggesting character displacement in these guilds. 6. However, when we corrected for clines, predictions of competition theory were not met - and often we obtained evidence for character convergence in sympatry. 7. This may suggest that the nature of the resource base may be more important than interspecific competition in shaping morphology and size in these carnivores. 8. Our results highlight the need to account for geographic variation when studying character displacement and cast some doubt on prevailing ideas regarding the effect of competition on morphological evolution.     

Involvement of facultative apomixis in inheritance of EPSPS gene amplification in glyphosate-resistant Amaranthus palmeri

The inheritance of glyphosate resistance in two Amaranthus palmeri populations (R1 and R2) was examined in reciprocal crosses (RC) and second reciprocal crosses (2RC) between glyphosate-resistant (R) and -susceptible (S) parents of this dioecious species. R populations and Female-R × Male-S crosses contain higher 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS) gene copy numbers than the S population. EPSPS expression, EPSPS enzyme activity, EPSPS protein quantity, and level of resistance to glyphosate correlated positively with genomic EPSPS relative copy number. Transfer of resistance was more influenced by the female than the male parent in spite of the fact that the multiple copies of EPSPS are amplified in the nuclear genome. This led us to hypothesize that this perplexing pattern of inheritance may result from apomictic seed production in A. palmeri. We confirmed that reproductively isolated R and S female plants produced seeds, indicating that A. palmeri can produce seeds both sexually and apomictically (facultative apomixis). This apomictic trait accounts for the low copy number inheritance in the Female-S × Male-R offsprings. Apomixis may also enhance the stability of the glyphosate resistance trait in the R populations in the absence of reproductive partners.