Variation in anti-parasite behaviour and infection among larval amphibian species

Along with immune defences, many animals exhibit effective anti-parasite behaviours such as parasite avoidance and removal that influence their susceptibility to infection. Host ecology and life history influence investment into comparatively fixed defences such as innate immunity but may affect the strength of anti-parasite behaviours as well. We investigated activity levels in five different species of larval amphibian with varying life histories and ecology in control, novel food stimulus, and trematode parasite (Echinoparyphium sp.) threat conditions. There was a significant interaction of species and treatment given that American toad (Bufo americanus), wood frog (Lithobates sylvaticus), and bullfrog (Lithobates catesbeianus) tadpoles generally increased their activity when parasite infectious stages were present while grey tree frogs (Hyla versicolor) and northern leopard frogs (Lithobates pipiens) did not, even though activity was negatively related to infection. In addition, there was considerable variation among species in their susceptibility to parasitism, with infection prevalence ranging from 17 % in bullfrog tadpoles to 70 % in wood frogs. However, amphibian life history (larval and adult traits) was not related to parasitism or level of anti-parasite behaviour at the species level. Consequently, we suggest that future investigations include more species with a range of life history traits and also consider host ecology, particularly if conspicuous anti-parasite behaviours are more likely in amphibian species that experience a relatively low risk of predation.     

Exploring the structure and function paradigm

Advances in protein structure determination, led by the structural genomics initiatives have increased the proportion of novel folds deposited in the Protein Data Bank. However, these structures are often not accompanied by functional annotations with experimental confirmation. In this review, we reassess the meaning of structural novelty and examine its relevance to the complexity of the structure-function paradigm. Recent advances in the prediction of protein function from structure are discussed, as well as new sequence-based methods for partitioning large, diverse superfamilies into biologically meaningful clusters. Obtaining structural data for these functionally coherent groups of proteins will allow us to better understand the relationship between structure and function.     

Seasonal changes in the response of winter wheat to elevated atmospheric CO2 concentration grown in Open-Top Chambers and field tracking enclosures

Winter wheat was grown at ambient and elevated (ambient plus 350 μL L^–1) CO₂ concentrations in open top chambers and in field-tracking sun-lit climatized enclosures (elevated is 718 μL L^–1). There was no significant effect of CO₂ concentration on sheath, leaf and root biomass and leaf area in the early spring (January to April). 24-h canopy CO₂ exchange rate (CCER) was not significantly affected either. However, elevated CO₂ concentration increased CCER at midday, decreased evapotranspiration rate and increased instantaneous water-use-efficiency during early spring. Leaf, sheath and root nitrogen concentration per unit dry weight decreased and nonstructural carbohydrate concentration increased under elevated CO₂, and N-uptake per unit ground area decreased significantly (– 22%) towards the end of this period. These results contrast with results from the final harvest, when grain yield and biomass were increased by 19% under elevated CO₂. N concentration per dry weight was reduced by 5%, but N-uptake per unit ground area was significantly higher (+ 11%) for the elevated CO₂ treatment. 24-h and midday-CCER increased significantly more in late spring (period of 21 April to 30 May) (respectively by + 40% and 53%) than in the early spring (respectively 5% and 19%) in response to elevated CO₂. Midday evapotranspiration rate was reduced less by elevated CO₂ in the late spring (– 13%) than in early spring (– 21%). The CO₂ response of midday and 24-h CCER decreased again (+ 27% and + 23% resp.) towards the end of the growing season. We conclude that the low response to CO₂ concentration during the early spring was associated with a growth-restriction, caused by low temperature and irradiance levels. The reduction of nitrogen concentration, the increase of nonstructural carbohydrate, and the lower evapotranspiration indicated that CO₂ did have an effect towards the end of early spring, but not on biomass accumulation. Regression analysis showed that both irradiance and temperature affected the response to CO₂.     

SLIRP, a small SRA binding protein, is a nuclear receptor corepressor

Steroid receptor RNA activator (SRA), the only known RNA coactivator, augments transactivation by nuclear receptors (NRs). We identified SLIRP (SRA stem-loop interacting RNA binding protein) binding to a functional substructure of SRA, STR7. SLIRP is expressed in normal and tumor tissues, contains an RNA recognition motif (RRM), represses NR transactivation in a SRA- and RRM-dependent manner, augments the effect of Tamoxifen, and modulates association of SRC-1 with SRA. SHARP, a RRM-containing corepressor, also binds STR7, augmenting repression with SLIRP. SLIRP colocalizes with SKIP (Chr14q24.3), another NR coregulator, and reduces SKIP-potentiated NR signaling. SLIRP is recruited to endogenous promoters (pS2 and metallothionein), the latter in a SRA-dependent manner, while NCoR promoter recruitment is dependent on SLIRP. The majority of the endogenous SLIRP resides in the mitochondria. Our data demonstrate that SLIRP modulates NR transactivation, suggest it may regulate mitochondrial function, and provide mechanistic insight into interactions between SRA, SLIRP, SRC-1, and NCoR.     

Ecdysteroid synthesis by the ring gland of Drosophila melanogaster during late-larval,prepupal and pupal development

Radioimmunoassay has been used to determine the characteristics of ecdysteroid synthesis by ring glands and brain-ring gland preparations from late 3rd-instar larvae of Drosophila melanogaster cultured in vitro. The rate of synthesis and secretion is linear for at least 4 hr in culture. Using a 4-hr culture period, variation in the rate of ecdysteroid synthesis by brain-ring gland preparations during larval, prepupal and pupal development has been examined. The rate of synthesis and secretion is highest in late 3rd-instar larvae and decreases after puparium formation. During pupal development, at a time when the endogenous ecdysteroid titre is again increasing, the rate of ecdysteroid synthesis by brain-ring gland preparations remains low and is only 10% of that prior to puparium formation. It is, therefore, likely that the ring gland is not a major source of ecdysteroids during this period.     

Evolution of the relaxin-like peptide family

Background  

The relaxin-like peptide family belongs in the insulin superfamily and consists of 7 peptides of high structural but low sequence similarity; relaxin-1, 2 and 3, and the insulin-like (INSL) peptides, INSL3, INSL4, INSL5 and INSL6. The functions of relaxin-3, INSL4, INSL5, INSL6 remain uncharacterised. The evolution of this family has been contentious; high sequence variability is seen between closely related species, while distantly related species show high similarity; an invertebrate relaxin sequence has been reported, while a relaxin gene has not been found in the avian and ruminant lineages.     

Structural diversity of domain superfamilies in the CATH database

The CATH database of domain structures has been used to explore the structural variation of homologous domains in 294 well populated domain structure superfamilies, each containing at least three sequence diverse relatives. Our analyses confirm some previously detected trends relating sequence divergence to structural variation but for a much larger dataset and in some superfamilies the new data reveal exceptional structural variation. Use of a new algorithm (2DSEC) to analyse variability in secondary structure compositions across a superfamily sheds new light on how structures evolve. 2DSEC detects inserted secondary structures that embellish the core of conserved secondary structures found throughout the superfamily. Analysis showed that for 56% of highly populated superfamilies (>9 sequence diverse relatives), there are twofold or more increases in the numbers of secondary structures in some relatives. In some families fivefold increases occur, sometimes modifying the fold of the domain. Manual inspection of secondary structure insertions or embellishments in 48 particularly variable superfamilies revealed that although these insertions were usually discontiguous in the sequence they were often co-located in 3D resulting in a larger structural motif that often modified the geometry of the active site or the surface conformation promoting diverse domain partnerships and protein interactions. These observations, supported by automatic analysis of all well populated CATH families, suggest that accretion of small secondary structure insertions may provide a simple mechanism for evolving new functions in diverse relatives. Some layered domain architectures (e.g. mainly-beta and alpha-beta sandwiches) that recur highly in the genomes more frequently exploit these types of embellishments to modify function. In these architectures, aggregation occurs most often at the edges, top or bottom of the beta-sheets. Information on structural variability across domain superfamilies has been made available through the CATH Dictionary of Homologous Structures (DHS).     

Immunohistochemical markers of human sebaceous gland differentiation

Cryostat sections of human skin were stained with monoclonal antibodies to involucrin, a range of cytokeratins, epithelial membrane antigen (EMA), and an ovarian cystadenocarcinoma antibody (OM1) to identify combinations of antibodies that could be used to discriminate between basal and differentiated sebocytes and other cell types present in the pilosebaceous unit. Both the EMA and OM1 monoclonal antibodies specifically recognized differentiated sebocytes. No staining of basal sebocytes or other epidermal cell types was seen. Differentiated (but not basal) sebocytes were also stained by a cytokeratin 10 antibody (LH2). Conversely, the basal sebocytes were recognized by an antibody specific to basal keratinocytes (LH6). Cells of the sebaceous duct stained with both LH2 and LH6 and also with the anti-involucrin monoclonal antibody. Cytokeratin 4 has been detected in sebaceous glands by protein analysis but has not previously been detectable immunohistochemically. We show by immunofluorescence after limited proteolysis that cytokeratin 4 epitopes are distributed in all sebaceous gland cells, including the duct cells.     

Ca2+, annexins, and GTP modulate exocytosis from maize root cap protoplasts

Protoplasts isolated from root cap cells of maize were shown to secrete fucose-rich polysaccharides and were used in a patch-clamp study to monitor changes in whole-cell capacitance. Ca2+ was required for exocytosis, which was measured as an increase in cell capacitance during intracellular dialysis with Ca2+ buffers via the patch pipette. Exocytosis was stimulated significantly by small increases above normal resting [Ca2+]. In the absence of Ca2+, protoplasts decreased in size. In situ hybridization showed significant expression of the maize annexin p35 in root cap cells, differ-entiating vascular tissue, and elongating cells. Dialysis of protoplasts with maize annexins stimulated exocytosis at physiological [Ca2+], and this could be blocked by dialysis with antibodies specific to maize annexins. Dialysis with milli-molar concentrations of GTP strongly inhibited exocytosis, causing protoplasts to decrease in size. GTPgammaS and GDPbetaS both caused only a slight inhibition of exocytosis at physiological Ca2+. Protoplasts were shown to internalize plasma membrane actively. The results are discussed in relation to the regulation of exocytosis in what is usually considered to be a constitutively secreting system; they provide direct evidence for a role of annexins in exocytosis in plant cells.