Nuclear components responsible for the retention of steroid--receptor complexes, especially from the standpoint of the specifcity of hormonal responses.

1. By covalently linking nuclear components from hormone-sensitive cells to Sepharose 2B, it is possible to investigate the interaction between nuclear components and cytoplasmic receptor-steroid complexes by affinity chromatography. 2. Many factors are implicated in the specifity of nuclear-cytoplasmic interactions, including the nature of the nuclear components, the presence of the cytoplasmic receptor protein and the provision of the appropriate steroid ligand. 3. Two distinct sets of binding sites are present in nuclear extracts immobilized to Sepharose 2B, namely a small number of specific high-affinity sites and a larger number of non-specific low affinity-sites. 4. Considerable evidence supports the importance of the high-affinity binding sites in the manifestation of hormonal specificity in different tissues. Although the study has centred largely on androgenresponsive systems, the findings are germane to cytoplasmic-nuclear interactions in general. 5. The high-affinity or acceptor sites in nuclear extracts reside in the basic but non-histone protein fraction. 6. Hormonal specificity is seemingly maintained by both the cytoplasmic and nuclear components, and the results are discussed in the context of the mechanism of action of steroid hormones.     

The maize gene maternal derepression of r1 encodes a DNA glycosylase that demethylates DNA and reduces siRNA expression in the endosperm

Demethylation of transposons can activate the expression of nearby genes and cause imprinted gene expression in the endosperm; this demethylation is hypothesized to lead to expression of transposon small interfering RNAs (siRNAs) that reinforce silencing in the next generation through transfer either into egg or embryo. Here we describe maize (Zea mays) maternal derepression of r1 (mdr1), which encodes a DNA glycosylase with homology to Arabidopsis thaliana DEMETER and which is partially responsible for demethylation of thousands of regions in endosperm. Instead of promoting siRNA expression in endosperm, MDR1 activity inhibits it. Methylation of most repetitive DNA elements in endosperm is not significantly affected by MDR1, with an exception of Helitrons. While maternally-expressed imprinted genes preferentially overlap with MDR1 demethylated regions, the majority of genes that overlap demethylated regions are not imprinted. Double mutant megagametophytes lacking both MDR1 and its close homolog DNG102 result in early seed failure, and double mutant microgametophytes fail pre-fertilization. These data establish DNA demethylation by glycosylases as essential in maize endosperm and pollen and suggest that neither transposon repression nor genomic imprinting is its main function in endosperm.

Demethylation by DNA glycosylases is important for endosperm development, but only a subset of the affected loci are imprinted, suggesting demethylation may have additional functions.

IN A NUTSHELL Background: In 1970, Jerry Kermicle reported that maize kernels could have dramatically different pigmentation depending on which parent the r1 gene is inherited from. This was the first discovery of many genomically imprinted genes that are selectively expressed from the maternal genome in endosperm. Later, Kermicle also discovered a mutant with poor maternal r1 expression. He hypothesized that the normal function of the mutated gene would be to derepress maternal r1; hence the name maternal depression of r1 (mdr1). The identify of mdr1 has remained unknown since then, but studies using Arabidopsis thaliana have revealed that DNA demethylation by enzymes called DNA glycosylases is important for expression of some maternally inherited genes in endosperm. Question: We wanted to identify the mdr1 gene. We hypothesized that mdr1 would reveal insights into molecular mechanisms of genomic imprinting in maize. Findings: We discovered that mdr1 encodes one of two DNA glycosylases with high expression in endosperm. We found that at least one of the two must be functional for endosperm to develop normally, but the one encoded by mdr1 is expressed higher. Surprisingly, most of the genes the mdr1 DNA glycosylase demethylates do not appear to be genomically imprinted, and about half the DNA it demethylates is not even near genes. These findings suggest that DNA glycosylases also have an undiscovered function unrelated to genomic imprinting in endosperm. Next steps: We want to know how specific regions in the genome are targeted for demethylation. What distinguishes these regions from other regions in endosperm? And what keeps them from being demethylated in other tissues? On the flip side, little is known about the effect of demethylation in endosperm, other than genomic imprinting. We want to know what effect DNA demethylation by DNA glycosylases has on chromatin structure and why it is important.     

Influence of genetic predisposition to diabetes and obesity on mitochondrial function

Inbred mice with the mutation diabetes C57BL/KsJ db+/db+ and the mutation obese C57BL/6J ob/ob displayed a total liver mitochondrial capacity to oxidize glutamate or succinate which was approximately eight times greater than the capacity of the C57BL/6J +/+ control mice. This increase in oxidation capacity was estimated by multiplying the observed twofold increase in each of the following components: total liver weight, the mitochondrial protein content per gram of liver, and glutamate or succinate respiration activity per milligram of liver mitochondrial protein. No significant difference in liver mitochondrial function and capacity for oxidation was observed between db+/db+ and ob/ob mutants, which indicated that these results may be primarily mediated by the genetic factors responsible for obesity and hyperphagia in these mutants, and not by the genetic traits associated with diabetes. These findings may provide a biochemical foundation in support of the thrifty gene hypothesis.     

Nonlinear systems in medicine

Many achievements in medicine have come from applying linear theory to problems. Most current methods of data analysis use linear models, which are based on proportionality between two variables and/or relationships described by linear differential equations. However, nonlinear behavior commonly occurs within human systems due to their complex dynamic nature; this cannot be described adequately by linear models. Nonlinear thinking has grown among physiologists and physicians over the past century, and non-linear system theories are beginning to be applied to assist in interpreting, explaining, and predicting biological phenomena. Chaos theory describes elements manifesting behavior that is extremely sensitive to initial conditions, does not repeat itself and yet is deterministic. Complexity theory goes one step beyond chaos and is attempting to explain complex behavior that emerges within dynamic nonlinear systems. Nonlinear modeling still has not been able to explain all of the complexity present in human systems, and further models still need to be refined and developed. However, nonlinear modeling is helping to explain some system behaviors that linear systems cannot and thus will augment our understanding of the nature of complex dynamic systems within the human body in health and in disease states.     

Genetic map of the opp (Oligopeptide permease) locus of Salmonella typhimurium.

The uptake of peptides by Salmonella typhimurium is mediated by three apparently independent transport systems. One of these systems, the oligopeptide permease, is encoded by a genetic locus (opp) which has been mapped at 34 min on the S. typhimurium chromosomal map. We accurately mapped the location of opp by cotransduction frequencies and by deletion analysis and show that the gene order for this region of the chromosome is cysB-trp-tonB-opp-galU-tdk. All opp mutants, independently isolated by a variety of means, mapped at this one locus, between tonB and galU. Spontaneous and transposon Tn10-generated deletions were used to construct a fine-structure genetic map of opp. Evidence is presented which indicates that opp covers a 5- to 6-kb segment of DNA and is therefore likely to consist of more than one gene.     

Larval survival and development of susceptible and resistant Ostrinia nubilalis (Lepidoptera: Pyralidae) on diet containing Bacillus thuringiensis

Abstract 1 Larval survival and development of Dipel‐susceptible and ‐resistant strains of European corn borer, Ostrinia nubilalis (Hübner), were assayed using diets incorporating low doses of a commercial formulation of Bacillus thuringiensis var. kurstaki Berliner (Dipel ES). 2 Larval mortality, growth and development, pupation rate and pupal weight were not significantly different between Dipel‐susceptible and ‐resistant strains when larvae were reared on a nontoxic control diet. 3 Larval mortality of Dipel‐resistant larvae did not significantly change as Dipel concentration increased at the tested concentrations, whereas mortality of Dipel‐susceptible larvae increased dramatically as Dipel concentration increased. 4 Larval development was significantly delayed when larvae were fed diets containing low doses of Dipel. 5 Pupation rate and pupal body weight declined as Dipel concentration increased but it decreased faster for the susceptible strain than for the resistant strain.     

Complement driven innate immune response to malaria: fuelling severe malarial diseases

Severe malaria remains a major cause of global mortality. The innate immune response to infection is a key determinant of malaria severity and outcome. The complement system plays a key role in initiating and augmenting innate immune responses, including inflammation, endothelial activation, opsonization and coagulation, processes which have been implicated in malaria pathogenesis. In this review, we discuss the evidence supporting a role for excessive complement activation in the pathogenesis of severe malaria.     

A sequence-specific function for the N-terminal signal-like sequence of the TonB protein

TonB is a proline-rich protein which provides a functional link between the inner and outer membranes of Gram-negative bacteria. TonB is anchored to the inner membrane via an N-terminal signal-like sequence and spans the periplasm, interacting with transport receptors in the outer membrane. We have investigated the role of the N-terminal signal-like peptide in TonB function. Replacement of the N-terminal sequence with heterologous sequences indicates that it has at least three distinct rotes in TonB function: (i) to facilitate translocation of TonB across the cytoplasmic membrane; (ii) to anchor TonB to the cytoplasmic membrane; (iii) a sequence-specific functional interaction with the ExbBD proteins.     

Passerines may be sufficiently plastic to track temperature‐mediated shifts in optimum lay date

Projecting the fates of populations under climate change is one of global change biology's foremost challenges. Here, we seek to identify the contributions that temperature‐mediated local adaptation and plasticity make to spatial variation in nesting phenology, a phenotypic trait showing strong responses to warming. We apply a mixed modeling framework to a Britain‐wide spatiotemporal dataset comprising >100 000 records of first egg dates from four single‐brooded passerine bird species. The average temperature during a specific time period (sliding window) strongly predicts spatiotemporal variation in lay date. All four species exhibit phenological plasticity, advancing lay date by 2–5 days °C^?1. The initiation of this sliding window is delayed further north, which may be a response to a photoperiod threshold. Using clinal trends in phenology and temperature, we are able to estimate the temperature sensitivity of selection on lay date (B), but our estimates are highly sensitive to the temporal position of the sliding window. If the sliding window is of fixed duration with a start date determined by photoperiod, we find B is tracked by phenotypic plasticity. If, instead, we allow the start and duration of the sliding window to change with latitude, we find plasticity does not track B, although in this case, at odds with theoretical expectations, our estimates of B differ across latitude vs. longitude. We argue that a model combining photoperiod and mean temperature is most consistent with current understanding of phenological cues in passerines, the results from which suggest that each species could respond to projected increases in spring temperatures through plasticity alone. However, our estimates of B require further validation.