Toward a physiological explanation of juvenile growth curves

Juvenile growth curves are generally sigmoid in shape: Growth is initially nearly exponential, but it slows to near zero as the animal approaches maturity. The drop‐off in growth rate is puzzling because, everything else being equal, selection favors growing as fast as possible. Existing theory posits sublinear scaling of resource acquisition with juvenile body mass and linear scaling of the requirement for maintenance, so the difference, fuel for growth, decreases as the juvenile increases in size. Experimental evidence, however, suggests that maintenance metabolism increases sublinearly not linearly with size. Here, we develop a new theory consistent with the experimental evidence. Our theory is based on the plausible assumption that there is a trade‐off in the capacity of capillaries to supply growing and developed cells. As the proportion of non‐growing cells increases, they take up more macromolecules from the capillaries, leaving fewer to support growing cells. The predicted growth curves are realistic and similar to those of previous models (Bertalanffy, Gompertz, and Logistic) but have the advantage of being derived from a plausible physiological model. We hope that our focus on resource delivery in capillaries will encourage new experimental work to identify the detailed physiological basis of the trade‐off underlying juvenile growth curves

Sir William Dawson (1820–1899): a very modern paleobotanist

Sir William Dawson was one of Canada’s most influential Nineteenth Century geologists. Although a lifelong opponent of the concept of evolution, a stance that resulted in him being sidelined by the scientific community, he made enormous contributions to Pennsylvanian paleobotany, especially at the Joggins fossil cliffs of Nova Scotia. Key to Dawson’s success was his recognition of the importance of a field-based research program, in which fossil plants could be observed in their precise geological context over a sustained period of time. Uniquely trained as both geologist and botanist, he was skilled in the microscopic analysis of permineralized plant anatomy, and appreciated the enormous potential of fossil charcoal as an untapped source of systematic information. Arguably his most extraordinary insights came in the field of plant taphonomy, in which studies of modern sedimentary processes and environments were used to interpret the rock record. His analysis of fossil plants in their sedimentary context allowed Pennsylvanian coal swamp communities, dominated by lycopsids and calamiteans, to be distinguished from the coniferopsid forests, which occupied mountainous regions further inland. The lasting significance of Dawson’s paleobotanical work is emphasized by many recent papers concerning the Pennsylvanian coal measures of Atlantic Canada, which have either directly built on research topics that Dawson initiated, or have confirmed hypotheses that Dawson framed. Until recent times, the discipline of paleobotany has been dominated by systematic fossil plant description with little or no reference to geological context. By virtue of his distinctively holistic approach, synthesizing all available geological and botanical data, Dawson is marked out from his contemporaries. His methodology does not appear old-fashioned even today, and it is therefore with justification that we describe him as a very modern paleobotanist. Resumé Sir William Dawson a été l’un des géologues les plus influents du 19e siècle au Canada. Même s’il s’est opposé toute sa vie au concept de l’évolution, une position qui a amené le milieu scientifique à l’ignorer, il a énormément contribué à la paléobotanique pennsylvanienne, spécialement dans les falaises fossilifères de Joggins de la Nouvelle-Écosse. La clé du succès de Dawson réside dans le fait qu’il avait reconnu l’importance d’un programme de recherche sur le terrain prévoyant l’observation des plantes fossiles dans leur milieu géologique particulier pendant une période de temps prolongée. Grâce à sa formation unique de géologue et de botaniste, il possédait la compétence voulue pour réaliser une analyse microscopique de l’anatomie des plantes perminéralisées et il comprenait le potentiel énorme du charbon de bois fossile comme source inexploitée de données systématiques. On pourrait soutenir que ses idées les plus extraordinaires se sont manifestées dans le domaine de la taphonomie végétale, dans lequel des études d’environnements et de processus sédimentaires modernes ont servi à interpréter des antécédents lithologiques. Ses analyses de plantes fossiles dans leur contexte sédimentaire ont permis de distinguer les communautés des marécages houillers pennsylvaniens, dans lesquels prédominent les lycopsides et les calamites, des forêts coniféropsides, qui occupaient les régions montagneuses plus à l’intérieur des terres. De nombreuses communications récentes au sujet des couches houillères pennsylvaniennes des provinces de l’Atlantique, qui s’appuient directement sur des sujets de recherches amorcées par Dawson ou ayant confirmé des hypothèses formulées par Dawson, mettent en relief l’importance durable des travaux paléobotaniques de Dawson. La discipline de la paléobotanique a jusqu’à tout récemment été dominée par des descriptions systématiques de plantes fossiles évoquant à peine ou n’évoquant pas du tout le contexte géologique. Dawson s’est démarqué de ses contemporains au moyen de son approche nettement holistique en réalisant une synthèse de toutes les données géologiques et botaniques accessibles. Sa méthode de travail ne semble pas rétrograde, même aujourd’hui, et il est par conséquent tout à fait justifié que nous le décrivions en tant que paléobotaniste très moderne

Culture medium, gas atmosphere and MAPK inhibition affect regulation of RNA-binding protein targets during mouse preimplantation development.

During oogenesis, mammalian oocytes accumulate maternal mRNAs that support the embryo until embryonic genome activation. RNA-binding proteins (RBP) may regulate the stability and turnover of maternal and embryonic mRNAs. We hypothesised that varying embryo culture conditions, such as culture medium, oxygen tension and MAPK inhibition, affects regulation of RBPs and their targets during preimplantation development. STAU1, ELAVL1, KHSRP and ZFP36 proteins and mRNAs were detected throughout mouse preimplantation development, whereas Elavl2 mRNA decreased after the two-cell stage. Potential target mRNAs of RBP regulation, Gclc, Slc2a1 and Slc7a1 were detected during mouse preimplantation development. Gclc mRNA was significantly elevated in embryos cultured in Whitten\u27s medium compared with embryos cultured in KSOMaa, and Gclc mRNA was elevated under high-oxygen conditions. Inhibition of the p38 MAPK pathway reduced Slc7a1 mRNA expression while inhibition of ERK increased Slc2a1 mRNA expression. The half-lives of the potential RBP mRNA targets are not regulated in parallel; Slc2a1 mRNA displayed the longest half-life. Our results indicate that mRNAs and proteins encoding five RBPs are present during preimplantation development and more importantly, demonstrate that expression of RBP target mRNAs are regulated by culture medium, gas atmosphere and MAPK pathways

The Athol Syncline: tectonic evolution of a Westphalian A-B depocentre in the Maritimes Basin, Nova Scotia

In the western Cumberland Basin, Nova Scotia, significant thickening of Westphalian A-B strata towards the axis of the Athol Syncline suggests that development of the syncline coincided with that of the depocentre. This contrasts with stratigraphic relations typical of the Late Paleozoic Maritimes Basin where thinning of Westphalian B strata indicates regional, Late Carboniferous erosion or non-deposition. Post-depositional structural complications within the Athol Syncline include truncation of its southern limb by a near-vertical, east-west zone of strike-slip faulting. This zone, the Athol-Sand Cove Fault Zone (ASCFZ), has been correlated to the west with a complex zone of faulting exposed on the coast of Chignecto Bay where numerous normal, reverse and oblique-slip displacements suggest predominantly brittle deformation and changes in the sense of strike slip. To the east, the ASCFZ splays north into the Springhill coalfield where it is responsible for complex patterns of normal, reverse and strike-slip faulting within Westphalian A-B coal measures. Major Late Carboniferous strike-slip faults adjacent to the Athol Syncline record dextral motion south of the Cumberland Basin (on the east-west Cobequid Fault) and possible sinistral motion along the basin's northwestern margin (on the northeast-southwest Harvey-Hopewell Fault). These faults are respectively interpreted to be synthetic and antithetic structures related to a regional dextral shear regime in which the east-northeast-west-southwest Athol Syncline and its associated depocentre formed in response to the direction of local compression during basin development. However, kinematic analyses indicate that post-depositional motion on the ASCFZ was predominantly sinistral. Development of the Athol Syncline is therefore interpreted to have been controlled by dextral, syndepositional transpression during the Late Carboniferous, whereas later, post-depositional displacement across the ASCFZ reflects predominantly sinistral transtension and may be related to the opening of the Fundy Basin which reversed the sense of regional shear during the Middle Triassic. RÉSUMÉ Dans la partie ouest du bassin de Cumberland en Nouvelle Écosse, un épaississement important des strates du Westphalien A-B vers Paxe du synclinal d'Athol suggère que le développement du synclinal à coincide avec celui du centre de déposition. Ceci contraste avec les relations stratigraphiques typiques du bassin des Maritimes du Paléozoique tardif où L’amincissement des strates du Westphalien B indique une erosion régionale ou une absence de déposition au Carbonifere tardif. Les complications strucrurales après déposition à l'intérieur du synclinal d'Athol comprennent la troncature de son flanc sud par une zone de faille de décrochement est-ouest quasi-verticale. Cette zone, la zone de faille d'Athol-Sand Cove (ZFASC), à été correlée vers l'ouest avec une zone de faille complexe éxposée sur la côte de la baie de Chignecto où de nombreux déplacements normaux, inverses et obliques suggerent une déformation principalement cassante et des variations du sens de décrochement. Vers Test, la ZFASC se divise vers le nord dans le bassin houiller de Springhill où elle est responsable d'un reseau complexe de failles normales, inverses et de décrochement dans les séquences houilleres du Westphalien A-B. Les failles majeures de décrochement du Carbonifère tardif adjacentes au synclinal d'Athol montrent un mouvement dextre au sud du bassin de Cumberland (le long de la faille de Cobequid d'orientation est-ouest) et peut-être un mouvement senestre le long de la bordure nord-ouest du bassin (le long de la faille d'Harvey-Hopewell, d'orientation nord-est - sud-ouest). Ces failles sont interpréters comme des structures synthétiques et antithétiques liées a un régime régional de décrochement dextre responsable de la formation du synclinal d'Athol d'orientation est-nord-est - ouest-sud-ouest et du centre de dépôt associé en réponse à la direction de compression locale durant le développement du bassin. Cependant, des analyses cinematiques indiquent que le mouvement postérieur au dépôt le long de la ZFASC était principalement senestre. Le développement du synclinal d'Athol est done interpréte comme ayant été controle par une transpression dextre contemporaine au dépôt durant le Carbonifère tardif, tandis que le emplacement plus tardif, posterieur au dépôt, de la ZFASC reflete principalement une transtension senestre et pourrait être liée à L’ouverture du bassin de Fundy qui a inversé le sens du cisaillement régional pendant le Trias moyen [Traduit par la rédaction

Disgust implicated in obsessive-compulsive disorder

Psychiatric classificatory systems consider obsessions and compulsions as forms of anxiety disorder. However, the neurology of diseases associated with obsessive-compulsive symptoms suggests the involvement of fronto-striatal regions likely to be involved in the mediation of the emotion of disgust, suggesting that dysfunctions of disgust should be considered alongside anxiety in the pathogenesis of obsessive-compulsive behaviours. We therefore tested recognition of facial expressions of basic emotions (including disgust) by groups of participants with obsessive-compulsive disorder (OCD) and with Gilles de la Tourette's syndrome (GTS) with and without co-present obsessive-compulsive behaviours (GTS with OCB; GTS without OCB). A group of people suffering from panic disorder and generalized anxiety were also included in the study. Both groups with obsessive-compulsive symptoms (OCD; GTS with OCB) showed impaired recognition of facial expressions of disgust. Such problems were not evident in participants with panic disorder and generalized anxiety, or for participants with GTS without obsessions or compulsions, indicating that the deficit is closely related to the presence of obsessive-compulsive symptoms. Participants with OCD were able to assign words to emotion categories without difficulty, showing that their problem with disgust is linked to a failure to recognize this emotion in others and not a comprehension or response criterion effect. Impaired recognition of disgust is consistent with the neurology of OCD and with the idea that abnormal experience of disgust may be involved in the genesis of obsessions and compulsions

Treatment with AICAR inhibits blastocyst development, trophectodermdifferentiation and tight junction formation and function in mice

STUDY QUESTION: What is the impact of adenosine monophosphate-activated protein kinase (AMPK) activation on blastocyst formation, gene expression, and tight junction formation and function? SUMMARY ANSWER: AMPK activity must be tightly controlled for normal preimplantation development and blastocyst formation to occur. WHAT IS KNOWN ALREADY: AMPK isoforms are detectable in oocytes, cumulus cells and preimplantation embryos. Cultured embryos are subject to many stresses that can activate AMPK. STUDY DESIGN, SIZE, DURATION: Two primary experiments were carried out to determine the effect of AICAR treatment on embryo development and maintenance of the blastocoel cavity. Embryos were recovered from superovulated mice. First, 2-cell embryos were treated with a concentration series (0-2000 μM) of AICAR for 48 h until blastocyst formation would normally occur. In the second experiment, expanded mouse blastocysts were treated for 9 h with 1000 μM AICAR. PARTICIPANTS/MATERIALS, SETTING, METHODS: Outcomes measured included development to the blastocyst stage, cell number, blastocyst volume, AMPK phosphorylation, Cdx2 and blastocyst formation gene family expression (mRNAs and protein measured using quantitative RT-PCR, immunoblotting, immunofluorescence), tight junction function (FITC dextran dye uptake assay), and blastocyst ATP levels. The reversibility of AICAR treatment was assessed using Compound C (CC), a well-known inhibitor of AMPK, alone or in combination with AICAR. MAIN RESULTS AND THE ROLE OF CHANCE: Prolonged treatment with AICAR from the 2-cell stage onward decreases blastocyst formation, reduces total cell number, embryo diameter, leads to loss of trophectoderm cell contacts and membrane zona occludens-1 staining, and increased nuclear condensation. Treatment with CC alone inhibited blastocyst development only at concentrations that are higher than normally used. AICAR treated embryos displayed altered mRNA and protein levels of blastocyst formation genes. Treatment of blastocysts with AICAR for 9 h induced blastocyst collapse, altered blastocyst formation gene expression, increased tight junction permeability and decreased CDX2. Treated blastocysts displayed three phenotypes: those that were unaffected by treatment, those in which treatment was reversible, and those in which effects were irreversible. LARGE SCALE DATA: Not applicable. LIMITATIONS, REASONS FOR CAUTION: Our study investigates the effects of AICAR treatment on early development. While AICAR does increase AMPK activity and this is demonstrated in our study, AICAR is not a natural regulator of AMPK activity and some outcomes may result from off target non-AMPK AICAR regulated events. To support our results, blastocyst developmental outcomes were confirmed with two other well-known small molecule activators of AMPK, metformin and phenformin. WIDER IMPLICATIONS OF THE FINDINGS: Metformin, an AMPK activator, is widely used to treat type II diabetes and polycystic ovarian disorder (PCOS). Our results indicate that early embryonic AMPK levels must be tightly regulated to ensure normal preimplantation development. Thus, use of metformin should be carefully considered during preimplantation and early post-embryo transfer phases of fertility treatment cycles. STUDY FUNDING AND COMPETING INTEREST(S): Canadian Institutes of Health Research (CIHR) operating funds. There are no competing interests

Simulations of Astrophysical Fluid Instabilities

We present direct numerical simulations of mixing at Rayleigh-Taylor unstable interfaces performed with the FLASH code, developed at the ASCI/Alliances Center for Astrophysical Thermonuclear Flashes at the University of Chicago. We present initial results of single-mode studies in two and three dimensions. Our results indicate that three-dimensional instabilities grow significantly faster than two-dimensional instabilities and that grid resolution can have a significant effect on instability growth rates. We also find that unphysical diffusive mixing occurs at the fluid interface, particularly in poorly resolved simulations.Comment: 3 pages, 1 figure. To appear in the proceedings of the 20th Texas Symposium on Relativistic Astrophysic

Large-Scale Simulations of Clusters of Galaxies

We discuss some of the computational challenges encountered in simulating the evolution of clusters of galaxies. Eulerian adaptive mesh refinement (AMR) techniques can successfully address these challenges but are currently being used by only a few groups. We describe our publicly available AMR code, FLASH, which uses an object-oriented framework to manage its AMR library, physics modules, and automated verification. We outline the development of the FLASH framework to include collisionless particles, permitting it to be used for cluster simulation.Comment: 3 pages, 3 figures, to appear in Proceedings of the VII International Workshop on Advanced Computing and Analysis Techniques in Physics Research (ACAT 2000), Fermilab, Oct. 16-20, 200