Genomic revelations of a mutualism: the pea aphid and its obligate bacterial symbiont

The symbiosis of the pea aphid Acyrthosphion pisum with the bacterium Buchnera aphidicola APS represents the best-studied insect obligate symbiosis. Here we present a refined picture of this symbiosis by linking pre-genomic observations to new genomic data that includes the complete genomes of the eukaryotic and prokaryotic symbiotic partners. In doing so, we address four issues central to understanding the patterns and processes operating at the A. pisum/Buchnera APS interface. These four issues include: (1) lateral gene transfer, (2) host immunity, (3) symbiotic metabolism, and (4) regulation

Fair open access: returning control of scholarly journals to their communities

he problem of how we should transition to open access is now urgent. The current situation is one of exorbitant subscription journals and expensive open-access ones, and to address it requires organised action from academics. The Fair Open Access Alliance, set up to facilitate the conversion of existing subscription journals to open access, is an example of such organisation. Alex Holcombe and Mark C. Wilson outline the group’s five Fair Open Access Principles and encourage all librarians, researchers, and administrators to work together to secure agreement to cancel subscriptions and to pool funds to pay for open access infrastructure

Aphid Thermal Tolerance Is Governed by a Point Mutation in Bacterial Symbionts

Symbiosis is a ubiquitous phenomenon generating biological complexity, affecting adaptation, and expanding ecological capabilities. However, symbionts, which can be subject to genetic limitations such as clonality and genomic degradation, also impose constraints on hosts. A model of obligate symbiosis is that between aphids and the bacterium Buchnera aphidicola, which supplies essential nutrients. We report a mutation in Buchnera of the aphid Acyrthosiphon pisum that recurs in laboratory lines and occurs in field populations. This single nucleotide deletion affects a homopolymeric run within the heat-shock transcriptional promoter for ibpA, encoding a small heat-shock protein. This Buchnera mutation virtually eliminates the transcriptional response of ibpA to heat stress and lowers its expression even at cool or moderate temperatures. Furthermore, this symbiont mutation dramatically affects host fitness in a manner dependent on thermal environment. Following a short heat exposure as juveniles, aphids bearing short-allele symbionts produced few or no progeny and contained almost no Buchnera, in contrast to aphids bearing symbionts without the deletion. Conversely, under constant cool conditions, aphids containing symbionts with the short allele reproduced earlier and maintained higher reproductive rates. The short allele has appreciable frequencies in field populations (up to 20%), further supporting the view that lowering of ibpA expression improves host fitness under some conditions. This recurring Buchnera mutation governs thermal tolerance of aphid hosts. Other cases in which symbiont microevolution has a major effect on host ecological tolerance are likely to be widespread because of the high mutation rates of symbiotic bacteria and their crucial roles in host metabolism and development

Ontogenetic shifts in fusion–rejection thresholds in a colonial marine hydrozoan, Hydractinia symbiolongicarpus

Abstract Like many modular organisms, genetically distinct colonies of the hydrozoan Hydractinia symbiolongicarpus naturally fuse to produce chimeras. One of the principal cooperative benefits of fusion arises from the increased size of the resulting chimeric individual, which may enhance survivorship. However, fusion also promotes conflict through competition between cell lineages for representation in reproductive tissues. Previous studies on H. symbiologicarpus show that, consistent with kin selection theory, a highly polymorphic self/non-self recognition system limits fusion to close kin. However, these recognition systems are intrinsically subject to error. Conspecific acceptance threshold theory predicts that as the costs and benefits of making recognition errors change, or the frequencies of encounters between acceptable and unacceptable kin vary, the recognition system should respond. Specifically, as the benefits of acceptance decline or the frequency of encounters with unacceptable individuals increases, the acceptance threshold should become more restrictive. We tested this hypothesis by monitoring changes in the expression of fusion/rejection behaviors of H. symbiolongicarpus during colony establishment, a period of high mortality when the sizedependent benefits of fusion may be changing most rapidly, and the frequency of encounters with close kin declines. Across seven full-sib families, fusion frequencies between pairs of sibling colonies declined from 73% for 3-day-old colonies to 58% by day 12. This decline is consistent with optimal acceptance threshold theory. However, the period of maximum decline also corresponds to an interval during which the recognition effector mechanism becomes fully functional, suggesting that the shift to a more restrictive conspecific acceptance threshold may reflect an intrinsic constraint on recognition system maturation

Destabilization of cortical dendrites and spines by BDNF

Particle-mediated gene transfer and two-photon microscopy were used to monitor the behavior of dendrites of individual cortical pyramidal neurons coexpressing green fluorescent protein (GFP) and brain-derived neurotrophic factor (BDNF). While the dendrites and spines of neurons expressing GFP alone grew modestly over 24-48 hr, coexpressing BDNF elicited dramatic sprouting of basal dendrites, accompanied by a regression of dendritic spines. Compared to GFP-transfected controls, the newly formed dendrites and spines were highly unstable. Experiments utilizing Trk receptor bodies, K252a, and overexpression of nerve growth factor (NGF) demonstrated that these effects were mediated by secreted BDNF interacting with extracellular TrkB receptors. Thus, BDNF induces structural instability in dendrites and spines, which, when restricted to particular portions of a dendritic arbor, may help translate activity patterns into specific morphological changes

Feedback cooling of a single trapped ion

Based on a real-time measurement of the motion of a single ion in a Paul trap, we demonstrate its electro-mechanical cooling below the Doppler limit by homodyne feedback control (cold damping). The feedback cooling results are well described by a model based on a quantum mechanical Master Equation.Comment: 4 pages, 3 figure

Defining a roadmap for harmonizing quality indicators in Laboratory Medicine: A consensus statement on behalf of the IFCC Working Group "laboratory Error and Patient Safety" and EFLM Task and Finish Group "performance specifications for the extra-analytical phases"

The improving quality of laboratory testing requires a deep understanding of the many vulnerable steps involved in the total examination process (TEP), along with the identification of a hierarchy of risks and challenges that need to be addressed. From this perspective, the Working Group \u201cLaboratory Errors and Patient Safety\u201d (WG-LEPS) of International Federation of Clinical Chemistry and Laboratory Medicine (IFCC) is focusing its activity on implementation of an efficient tool for obtaining meaningful information on the risk of errors developing throughout the TEP, and for establishing reliable information about error frequencies and their distribution. More recently, the European Federation of Clinical Chemistry and Laboratory Medicine (EFLM) has created the Task and Finish Group \u201cPerformance specifications for the extraanalytical phases\u201d (TFG-PSEP) for defining performance specifications for extra-analytical phases. Both the IFCC and EFLM groups are working to provide laboratories with a system to evaluate their performances and recognize the critical aspects where improvement actions are needed. A Consensus Conference was organized in Padova, Italy, in 2016 in order to bring together all the experts and interested parties to achieve a consensus for effective harmonization of quality indicators (QIs). A general agreement was achieved and the main outcomes have been the release of a new version of model of quality indicators (MQI), the approval of a criterion for establishing performance specifications and the definition of the type of information that should be provided within the report to the clinical laboratories participating to the QIs project

Cellular IP₆ Levels Limit HIV Production while Viruses that Cannot Efficiently Package IP₆ Are Attenuated for Infection and Replication

Summary: HIV-1 hijacks host proteins to promote infection. Here we show that HIV is also dependent upon the host metabolite inositol hexakisphosphate (IP6) for viral production and primary cell replication. HIV-1 recruits IP6 into virions using two lysine rings in its immature hexamers. Mutation of either ring inhibits IP6 packaging and reduces viral production. Loss of IP6 also results in virions with highly unstable capsids, leading to a profound loss of reverse transcription and cell infection. Replacement of one ring with a hydrophobic isoleucine core restores viral production, but IP6 incorporation and infection remain impaired, consistent with an independent role for IP6 in stable capsid assembly. Genetic knockout of biosynthetic kinases IPMK and IPPK reveals that cellular IP6 availability limits the production of diverse lentiviruses, but in the absence of IP6, HIV-1 packages IP5 without loss of infectivity. Together, these data suggest that IP6 is a critical cofactor for HIV-1 replication