Look who's talking too: graduates developing skills through communication

Greater opportunities for young scientists to present their doctoral research to large general audiences will encourage development of transferable skills and involvement in the scientific community. We look at ways students communicate their research and explore the benefits of student-led meetings. The organization of the first Sanger-Cambridge Ph.D. Symposium provides an example of how students can act to establish forums for their work and we call on other young scientists to do the same.     

Look who's talking: nuclear receptors in the liver and gastrointestinal tract

The Nuclear Receptors in Liver and Digestive Diseases research workshop was held in Rockville, Maryland, on November 7 and 8, 2007, under the auspices of the National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health. Over 130 researchers from around the world gathered to assess the pathophysiology of nuclear receptors in the liver and gastrointestinal tract and to explore their potential use as therapeutic targets. This review covers some of the highlights of the meeting, including important areas of future investigation.     

Look who's talking: communication and quorum sensing in the bacterial world

For many years bacteria were considered primarily as autonomous unicellular organisms with little capacity for collective behaviour. However, we now appreciate that bacterial cells are in fact, highly communicative. The generic term 'quorum sensing' has been adopted to describe the bacterial cell-to-cell communication mechanisms which co-ordinate gene expression usually, but not always, when the population has reached a high cell density. Quorum sensing depends on the synthesis of small molecules (often referred to as pheromones or autoinducers) that diffuse in and out of bacterial cells. As the bacterial population density increases, so does the synthesis of quorum sensing signal molecules, and consequently, their concentration in the external environment rises. Once a critical threshold concentration has been reached, a target sensor kinase or response regulator is activated (or repressed) so facilitating the expression of quorum sensing-dependent genes. Quorum sensing enables a bacterial population to mount a co-operative response that improves access to nutrients or specific environmental niches, promotes collective defence against other competitor prokaryotes or eukaryotic defence mechanisms and facilitates survival through differentiation into morphological forms better able to combat environmental threats. Quorum sensing also crosses the prokaryotic-eukaryotic boundary since quorum sensing-dependent signalling can be exploited or inactivated by both plants and mammals.     

Fumonisins: current research trends in developmental toxicology

Fumonisin B₁ (FB₁) is a mycotoxin produced byFusarium verticillioides that is found in maize and maize-based foods. Reproductive studies in CD1 mice, rats and rabbits initially found no evidence that fumonisins are teratogenic. However, more recent findings suggest that they might increase the risk of neural tube defects (NTDs) in populations consuming large amounts of fumonisin-contaminated corn. When ≥15 mg/kg body weight fumonisin B₁ (FB₁) was given to pregnant LM/Bc mice by intraperitoneal (ip) injection, all litters were positive for NTDs. To determine if NTD induction is unique to the inbred LM/Bc mouse strain, NTD induction in LM/Bc and CD1 mice was compared: (a) in a study in whichF. verticillioides culture material providing ≤150 ppm FB₁ was fed to female mice before and during gestation, and (b) in a study in which FB₁ was given by ip injection to CD1 dams on gestation days 7 and 8, the critical time for NTD development. In the feeding study, one of five LM/Bc litters from dams fed the 150 ppm FB₁ diet was positive for NTDs whereas no NTDs were found in the CD1 litters. In the ip injection study, 40% of the litters at the highest dose tested, 45 mg/kg body weight, were positive for NTDs and one of nine low-dose (15 mg/kg body weight) litters was also positive. Thus, FB₁ induced NTDs in both LM/Bc and CD1 mice although the latter strain appears less sensitive. Comparative investigations using these strains will be useful for elucidating the mechanisms underlying fumonisin-induced NTDs in mice and determining the suitability of mouse models for studying the relationships between fumonisins and NTDs in humans.     

Body size and cell size in Drosophila: the developmental response to temperature

In Drosophila, like most ectotherms, development at low temperature reduces growth rate but increases final adult size. Cultures were shifted from 25 degrees C to low (16.5 degrees C) or to high (29 degrees C) temperature at regular intervals through larval and pupal stages, and the flies of both sexes showed an increase or decrease, respectively, in the size of thorax, wing and abdominal tergite. Size changes in the wing blade resulted from changes in the size of the epidermal cells (with only a small increase in cell number in males reared at low temperature). The temperature-shifts became less effective as they were made at successively later developmental stages, demonstrating a cumulative effect of temperature on adult size. The thorax and wing develop from the same imaginal disc, with most cell division occurring in larval stages, but they differ in timing of temperature sensitivity, which extends only to pupariation or into the late pupal stage, respectively. Growth of the adult abdomen occurs largely after pupariation but its size is temperature-sensitive through both larval and pupal stages. We discuss growth control in Drosophila and the likely effects of temperature on food assimilation, growth efficiency and allocation of nutrients to the production of different tissues.     

A matter of size: developmental control of organ size in plants

The intrinsic size of plant organs is determined by developmental signals, yet the molecular and genetic mechanisms that control organ size are largely unknown. Ongoing functional analysis of Arabidopsis genes is defining important regulators involved in these mechanisms. Key features of this control are the coordinated activation of growth and cell division by growth regulators and the maintenance of meristematic competence by the ANT gene, which acts as an organ-size checkpoint. Alterations of genome size by polyploidization and endoreduplication can reset this checkpoint by ploidy-dependent, epigenetically regulated differential gene expression. In addition, the regulation of polarized growth and phytohormone signaling also affect final organ size. These findings reveal unique aspects of plant organ-size control that are distinct from animal organ-size control.     

Ontogeny as a whole: Some developmental trends

In many animal groups, rudimentary organs of adult organisms appear at early stages of egg cleavage, when there is no trace of morphological differentiation. More than half a century ago, I. I. Schmalhausen developed a profound concept of integrity of the organism in the course of development. He emphasized that mutual adaptation of organs is based on correlations, involving the so-called nonhereditary modifications, which are transformed into hereditary traits by means of natural selection. There are many exceptions to the biogenetic law, as it was understood by de Beer. In particular, embryo of the pouched tree frog Gastrotheca shows a retarded development and is spread over the yolk surface. As a result, it becomes similar somewhat to embryos of amniotes. After the metamorphosis, Xenopus returns to ammonotelism. The integrity of ontogeny at the molecular level has much in common with the neutrality theory.     

Position and developmental trends in fibrinolytic therapy

Increasing insight into the mechanism of fibrinolysis and particularly into the formation and release of plasminogen activator has led to more effective thrombolytic therapy. The understanding of the mechanism of thrombolysis has provided the possibility to improve the therapeutic effects of the fibrinolytic agents streptokinase and urokinase. Further advances in thrombolytic therapy are expected by the use of the plasminogen activator from tissue endothelium and pro-urokinase. Acylation of fibrinolytic enzymes will lead to beneficial effects (depot effect, protection from intrinsic inhibitors). Due to the extensive research into substances with fibrinolytic and thrombolytic effects a new generation of activators of fibrinolysis is expected that interfere with the biosynthesis and release of plasminogen activator of the vessel wall and that are suited for treatment of hypofibrinolytic states.     

Genome size evolution in vertebrates: trends and constraints

1. Studies on the genomic evolution in vertebrates have highlighted the differences existing between anamniotes and amniotes, both in quantitative and compositional terms. 2. These differences do not seem to depend on a different tendency to genic amplification, but rather on the existence of more strict and efficient constraints in amniotes. 3. Some constraints, that may be defined as "intrinsic", would act directly on the genome; among these particularly important is the chiasma frequency during meiosis. 4. Other, "extrinsic", constraints, would act indirectly through genic products or through cell morphometric parameters. 5. The genome size increase seems to depend on various mechanisms. The most wide-spread one seems to be the amplification of interspersed repetitive and non-repetitive sequences.     

Climate change and temporal trends in body size: the case of rodents

A reduction in body size has been proposed as the third universal ecological response to global warming, after species distributional shifts and phenological changes. However, some recent studies raise doubts about the validity of this pattern, in particular for endotherms. Within this context, here we analyzed data on body mass (m_b) for 17 rodent species, covering (at least) the last six decades, together with data on temperature change and basal metabolic rate (BMR) for each species. We found that: 1) ten species (58.8%) showed no significant changes in m_b, while the remaining seven species (41.2%) decreased their size during the 20th century; 2) phylogenetic generalized linear mixed models indicate that there is a significant and negative effect of the year of collection on m_b; 3) the correlation coefficient between m_b and the year of collection (r_year) was not correlated with species mean m_b, species distributional range, the length of the time series, or the change in ambient temperature; and 4) the correlation between r_year and (residual) BMR was significant (and negative) only for species that do not use torpor. In summary, our results suggest that reductions in m_b are common among rodents, but we were unable to identify a clear cause behind these changes (e.g. some results support the energetic argument behind the Bergmann's rule but other do not). We concluded that with less than 0.5% of the extant (known) rodent species analyzed to date, we still are far from reaching a clear understanding of current patterns of variation in body size that are associated with global environmental change for this group.     

Evolutionary trends in body size of parasitic flatworms

Evolutionary trends in body size have been identified within several lineages, but not all have followed Cope's rule, which states that average body size within a taxon tends to increase over time. In organisms such as parasites, space constraints may have shaped the evolution of body sizes, favouring small-bodied taxa capable of exploiting new niches. Here, the average adult body sizes of families in three groups of parasitic flatworms, the Digenea and two clades of Monogenea (Monopisthocotylea and Polyopisthocotylea), are related to their clade rank. Clade rank reflects the number of branching events, and thus the total path length, between an extant family and the root of the phylogenetic tree. Among families of Digenea, all of which are endoparasites of vertebrates, there was no trend in body size evolution. In contrast, the Monopisthocotylea and Polyopisthocotylea, which are (with the exception of Polystomatidae and Sphyranuridae) ectoparasites of fish, revealed significant negative relationships between family body size and clade rank, suggesting an evolutionary trend of decreasing size. In addition, an analysis of body size distributions in monogenean families also provides support, albeit weak, for this trend. From an ancestor parasitic on the skin of fishes, monogeneans have diversified by colonizing other microhabitats on their hosts, including such space-limited sites as the gaps between secondary gill lamellae. Using a conservative likelihood ratio test, however, a random walk, or null model of evolution could not be discarded in favour of the directional trends mentioned above. Nevertheless, these results suggest that body size has taken different evolutionary paths in endo- and ectoparasitic flatworms.  © 2005 The Linnean Society of London, Biological Journal of the Linnean Society , 2005, 85 , 181–189.     

Genome size and developmental parameters in the homeothermic vertebrates.

Although unrelated to any intuitive notions of organismal complexity, haploid genome sizes (C values) are correlated with a variety of cellular and organismal parameters in different taxa. In some cases, these relationships are universal--notably, genome size correlates positively with cell size in each of the vertebrate classes. Other relationships are apparently relevant only in particular groups. For example, although genome size is inversely correlated with metabolic rate in both mammals and birds, no such relationship is found in amphibians. More recently, it has been suggested that developmental rate and (or) longevity are related to genome size in birds. In the present study, a large dataset was used to examine possible relationships between genome size and various developmental parameters in both birds and mammals. In neither group does development appear to be of relevance to genome size evolution (except perhaps indirectly in birds through the intermediation of body size and (or) within the rodents), a situation very different from that found in amphibians. These findings make it clear that genome size evolution cannot be understood without reference to the particular biology of the organisms under study.     

Temperature,size and developmental plasticity in birds

As temperatures increase, there is growing evidence that species across much of the tree of life are getting smaller. These climate change-driven size reductions are often interpreted as a temporal analogue of the observation that individuals within a species tend to be smaller in the warmer parts of the species'' range. For ectotherms, there has been a broad effort to understand the role of developmental plasticity in temperature–size relationships, but in endotherms, this mechanism has received relatively little attention in favour of selection-based explanations. We review the evidence for a role of developmental plasticity in warming-driven size reductions in birds and highlight insulin-like growth factors as a potential mechanism underlying plastic responses to temperature in endotherms. We find that, as with ectotherms, changes in temperature during development can result in shifts in body size in birds, with size reductions associated with warmer temperatures being the most frequent association. This suggests developmental plasticity may be an important, but largely overlooked, mechanism underlying warming-driven size reductions in endotherms. Plasticity and natural selection have very different constraining forces, thus understanding the mechanism linking temperature and body size in endotherms has broad implications for predicting future impacts of climate change on biodiversity.     

Environmental and scale-dependent evolutionary trends in the body size of crustaceans

The ecological and physiological significance of body size is well recognized. However, key macroevolutionary questions regarding the dependency of body size trends on the taxonomic scale of analysis and the role of environment in controlling long-term evolution of body size are largely unknown. Here, we evaluate these issues for decapod crustaceans, a group that diversified in the Mesozoic. A compilation of body size data for 792 brachyuran crab and lobster species reveals that their maximum, mean and median body size increased, but no increase in minimum size was observed. This increase is not expressed within lineages, but is rather a product of the appearance and/or diversification of new clades of larger, primarily burrowing to shelter-seeking decapods. This argues against directional selective pressures within lineages. Rather, the trend is a macroevolutionary consequence of species sorting: preferential origination of new decapod clades with intrinsically larger body sizes. Furthermore, body size evolution appears to have been habitat-controlled. In the Cretaceous, reef-associated crabs became markedly smaller than those in other habitats, a pattern that persists today. The long-term increase in body size of crabs and lobsters, coupled with their increased diversity and abundance, suggests that their ecological impact may have increased over evolutionary time.