Possible consequences of genes of major effect: transient changes in the G-matrix

Understanding the process of evolutionary divergence requires knowledge of the strength, form, and targets of selection, as well as the genetic architecture of the divergent traits. Quantitative genetic approaches to understanding multivariate selection and genetic response to selection have proven to be powerful tools in this endeavor, particularly with respect to short-term evolution. However, the application of quantitative genetic theory over periods of substantial phenotypic change is controversial because it requires that the requisite genetic parameters remain constant over the period of time in question. We show herein how attempts to determine the stability of key genetic parameters may be misled by the many genes of small effect type of genetic architecture generally assumed in quantitative genetics. The presence of genes of major effect (GOMEs) can alter the genetic variance-covariance matrix dramatically for brief periods of time, significantly alter the rate and trajectory of multivariate evolution, and thereby mislead attempts to reconstruct or predict long term evolution.     

Information encoding in the inferior temporal visual cortex: contributions of the firing rates and the correlations between the firing of neurons

The encoding of information by populations of neurons in the macaque inferior temporal cortex was analyzed using quantitative information-theoretic approaches. It was shown that almost all the information about which of 20 stimuli had been shown in a visual fixation task was present in the number of spikes emitted by each neuron, with stimulus-dependent cross-correlation effects adding for most sets of simultaneously recorded neurons almost no additional information. It was also found that the redundancy between the simultaneously recorded neurons was low, approximately 4% to 10%. Consistent with this, a decoding procedure applied to a population of neurons showed that the information increases approximately linearly with the number of cells in the population. AcknowledgementsThis research was supported by the Medical Research Council, grant PG9826105, by the Human Frontier Science Program, by the MRC Interdisciplinary Research Centre for Cognitive Neuroscience, and by the Wellcome Trust.     

Widespread polyphyly among Alopiinae snail genera: when phylogeny mirrors biogeography more closely than morphology

Consider a group of species that is evenly divided by an easily identifiable complex morphological character. Most biologists would assume that this character should provide better phylogenetic information than, say, the spatial distribution of these species over a fairly continuous 500-km radius area. Paradoxically, this is not the case among terrestrial snail genera in the clausiliid subfamily Alopiinae. Phylogenetic analysis using the nuclear markers ITS1/ITS2 and mitochondrial markers COI/12S reveals widespread homoplasy in the clausilial apparatus (a complex aperture-closing mechanism), and concomitant extensive polyphyly among Carinigera, Isabellaria, and Sericata. In contrast, phylogenetic relationships as revealed by molecular data are closely congruent with biogeography at a relatively small scale. A combination of extremely low vagility and extremely high morphological convergence has conspired to produce this unexpected result. Implications as to the function of the clausilial apparatus are discussed.     

Allogeneic T cells treated with amotosalen prevent lethal cytomegalovirus disease without producing graft-versus-host disease following bone marrow transplantation

Infusion of donor antiviral T cells can provide protective immunity for recipients of hemopoietic progenitor cell transplants, but may cause graft-vs-host disease (GVHD). Current methods of separating antiviral T cells from the alloreactive T cells that produce GVHD are neither routine nor rapid. In a model of lethal murine CMV (MCMV) infection following MHC-mismatched bone marrow transplantation, infusion of MCMV-immune donor lymphocytes pretreated with the DNA cross-linking compound amotosalen prevented MCMV lethality without producing GVHD. Although 95% of mice receiving 30 x 10(6) pretreated donor lymphocytes survived beyond day +100 without MCMV disease or GVHD, all mice receiving equivalent numbers of untreated lymphocytes rapidly died of GVHD. In vitro, amotosalen blocked T cell proliferation without suppressing MCMV peptide-induced IFN-gamma production by MCMV-primed CD8(+) T cells. In vivo, pretreated lymphocytes reduced hepatic MCMV load by 4-log(10) and promoted full hemopoietic chimerism. Amotosalen-treated, MCMV tetramer-positive memory (CD44(high)) CD8(+) T cells persisted to day +100 following infusion, and expressed IFN-gamma when presented with viral peptide. Pretreated T cells were effective at preventing MCMV lethality over a wide range of concentrations. Thus, amotosalen treatment rapidly eliminates the GVHD activity of polyclonal T cells, while preserving long-term antiviral and graft facilitation effects, and may be clinically useful for routine adoptive immunotherapy.     

Projection structure of the atractyloside-inhibited mitochondrial ADP/ATP carrier of Saccharomyces cerevisiae

ADP/ATP carriers in the inner mitochondrial membrane catalyze the exchange of cytosolic ADP for ATP synthesized in the mitochondrial matrix by ATP synthase and thereby replenish the eukaryotic cell with metabolic energy. The yeast ADP/ATP carrier (AAC3) was overexpressed, inhibited by atractyloside, purified, and reconstituted into two-dimensional crystals. Images of frozen hydrated crystals were recorded by electron microscopy, and a projection structure was calculated to 8-A resolution. The AAC3 molecule has pseudo 3-fold symmetry in agreement with the 3-fold sequence repeats that are typical of members of the mitochondrial carrier family. The density distribution is consistent with a bundle of six transmembrane alpha-helices with two or three short alpha-helical extensions closing the central pore on the matrix side. The AAC3 molecules in the crystal are arranged in symmetrical homo-dimers, but the translocation pore for adenine nucleotides lies in the center of the molecule and not along the dyad axis of the dimer.     

Lactococcus lactis as host for overproduction of functional membrane proteins

Lactococcus lactis has many properties that are ideal for enhanced expression of membrane proteins. The organism is easy and inexpensive to culture, has a single membrane and relatively mild proteolytic activity. Methods for genetic manipulation are fully established and a tightly controlled promoter system is available, with which the level of expression can be varied with the inducer concentration. Here we describe our experiences with lactococcal expression of the mechanosensitive channel, the human KDEL receptor and transporters belonging to the ABC transporter family, the major facilitator superfamily, the mitochondrial carrier family and the peptide transporter family. Previously published expression studies only deal with the overexpression of prokaryotic membrane proteins, but in this paper, experimental data are presented for the overproduction of mitochondrial and hydrogenosomal carriers and the human KDEL receptor. These eukaryotic membrane proteins were expressed in a functional form and at levels amenable to structural work.     

Genome-wide profiling of promoter recognition by the two-component response regulator CpxR-P in Escherichia coli

In Escherichia coli, the two-component Cpx system comprising the CpxA sensor kinase and the CpxR response regulator modulates gene expression in response to a variety of stresses including membrane-protein damage, starvation, and high osmolarity. To date, the few known CpxR-P target operons were mostly identified by genetic screens. To facilitate the discovery of all target operons, we derived a 15-bp weighted matrix for CpxR-P recognition that takes into account the relative base frequency at each nucleotide position. This matrix essentially consists of two tandem 5'-GTAAA-3' motifs separated by a 5-bp linker. All of the 15-bp stretches on both strands of the E. coli MG1655 genome were then scored for their degree of matching with the matrix and classified in statistical deviation groups. The effectiveness of this screening is indicated by the identification of eight new target operons (ung, ompC, psd, mviA, aroK, rpoErseABC, secA, and aer) among eleven candidates tested. Moreover, the matrix score correlates with the likelihood that a site is a true target and with the relative site affinity for CpxR-P in vitro. Our data indicate that some 100 operons are under direct CpxR-P control and that the signal transduction pathway interacts with several other control circuits in manners hitherto unanticipated.