BMC Biology - Latest Articles

Q&A: Antibiotic resistance: what more do we know and what more can we do?

Gerard Wright — 2013-05-17T00:00:00Z

Antibiotic resistance is both an ancient phenomenon and a worsening medical problem. Gerard Wright explains why, and what should be done about it.

On the origin of POU5F1

Stephen Frankenberg — 2013-05-09T00:00:00Z

Background: Pluripotency is a fundamental property of early mammalian development but it is currentlyunclear to what extent its cellular mechanisms are conserved in vertebrates or metazoans.POU5F1 and POU2 are the two principle members constituting the class V POU domainfamily of transcription factors, thought to have a conserved role in the regulation ofpluripotency in vertebrates as well as germ cell maintenance and neural patterning. They haveundergone a complex pattern of evolution which is poorly understood and controversial. Results: By analysing the sequences of POU5F1, POU2 and their flanking genes, we provide strongindirect evidence that POU5F1 originated at least as early as a common ancestor ofgnathostomes but became extinct in a common ancestor of teleost fishes, while both POU5F1and POU2 survived in the sarcopterygian lineage leading to tetrapods. Less divergent formsof POU5F1 and POU2 appear to have persisted among cartilaginous fishes. Conclusions: Our study resolves the controversial evolutionary relationship between teleost pou2 andtetrapod POU2 and POU5F1, and shows that class V POU transcription factors have existedat least since the common ancestor of gnathostome vertebrates. It provides a framework forelucidating the basis for the lineage-specific extinctions of POU2 and POU5F1.

Somatic and visceral nervous systems - an ancient duality

Paola Bertucci — 2013-04-30T00:00:00Z

The vertebrate nervous system is deeply divided into ‘somatic’ and ‘visceral’ subsystems that respond to external and internal stimuli, respectively. Molecular characterization of neurons in different groups of mollusks by Nomaksteinsky and colleagues, published in this issue of BMC Biology, reveals that the viscero-somatic duality is evolutionarily ancient, predating Bilateria.See research article: http://www.biomedcentral.com/1741-7007/11/53

Spatial and temporal in vivo analysis of circulating and sessile immune cells in mosquitoes: hemocyte mitosis following infection

Jonas King — 2013-04-30T00:00:00Z

Background: Mosquitoes respond to infection by mounting immune responses. The primary regulators of these immune responses are cells called hemocytes, which kill pathogens via phagocytosis and via the production of soluble antimicrobial factors. Mosquito hemocytes are circulated throughout the hemocoel (body cavity) by the swift flow of hemolymph (blood), and data show that some hemocytes also exist as sessile cells that are attached to tissues. The purpose of this study was to create a quantitative physical map of hemocyte distribution in the mosquito, Anopheles gambiae, and to describe the cellular immune response in an organismal context. Results: Using correlative imaging methods we found that the number of hemocytes in a mosquito decreases with age, but that regardless of age, approximately 75% of the hemocytes occur in circulation and 25% occur as sessile cells. Infection induces an increase in the number of hemocytes, and tubulin and nuclear staining showed that this increase is primarily due to mitosis, and more specifically autonomous cell division, by circulating granulocytes. The majority of sessile hemocytes are present on the abdominal wall, although significant numbers of hemocytes are also present in the thorax, head, and several of the appendages. Within the abdominal wall, the areas of highest hemocyte density are the periostial regions (regions surrounding the valves of the heart, or ostia), which are ideal locations for pathogen capture as these are areas of high hemolymph flow. Conclusions: These data describe the spatial and temporal distribution of mosquito hemocytes, and map the cellular response to infection throughout the hemocoel.

Ancient origin of somatic and visceral neurons

Marc Nomaksteinsky — 2013-04-30T00:00:00Z

Background: A key to understanding the evolution of the nervous system on a large phylogenetic scale is the identification of homologous neuronal types. Here, we focus this search on the sensory and motor neurons of bilaterians, exploiting their well-defined molecular signatures in vertebrates. Sensorimotor circuits in vertebrates are of two types: somatic (that sense the environment and respond by shaping bodily motions) and visceral (that sense the interior milieu and respond by regulating vital functions). These circuits differ by a small set of largely dedicated transcriptional determinants: Brn3 is expressed in many somatic sensory neurons, first and second order (among which mechanoreceptors are uniquely marked by the Brn3+/Islet+/Drgx+ signature), somatic motoneurons uniquely co-express Lhx3/4 and Mnx1, while the vast majority of neurons, sensory and motor, involved in respiration, blood circulation or digestion are molecularly defined by their expression and dependence on the pan-visceral determinant Phox2b. Results: We explore the status of the sensorimotor transcriptional code of vertebrates in mollusks, a lophotrochozoan clade that provides a rich repertoire of physiologically identified neurons. In the gastropods Lymnaea stagnalis and Aplysia californica, we show that homologues of Brn3, Drgx, Islet, Mnx1, Lhx3/4 and Phox2 differentially mark neurons with mechanoreceptive, locomotory and cardiorespiratory functions. Moreover, in the cephalopod Sepia officinalis, we show that Phox2 marks the stellate ganglion (in line with the respiratory --- i.e. visceral--- ancestral role of the mantle, its target organ), while the anterior pedal ganglion, which controls the prehensile and locomotory arms, expresses Mnx. Conclusions: Despite considerable divergence in overall neural architecture, a molecular underpinning for the functional allocation of neurons to interactions with the environment or to homeostasis was inherited from the urbilaterian ancestor by contemporary protostomes and deuterostomes.

Statistical support for the hypothesis of developmental constraint in marsupial skull evolution

C Bennett — 2013-04-26T00:00:00Z

Background: In contrast to placental neonates, in which all cranial bones are ossified, marsupial young have ossified only the bones of the oral region and the exoccipital at birth, in order to facilitate suckling at an early stage of development. Here, we test whether this heterochronic shift in the timing of cranial ossification has constrained cranial disparity in marsupials relative to placentals. 3-D landmark data were collected from the crania of a wide range of extant placentals and marsupials, as well as six fossil metatherians (the clade including extant marsupials and their stem relatives), using a laser scanner and a 3-D digitizer. Principal components analysis and delta variance tests were used to investigate the distribution and disparity of cranial morphology between different landmark sets (optimizing either number of landmarks or number of taxa) of the whole skull and of individual developmental or functional regions (neurocranium, viscerocranium, oral) for extant placentals and marsupials. Marsupial and placental data was also compared based on shared ecological aspects including diet, habitat and time of peak activity. Results: Results showed that the extant marsupial taxa investigated here occupy a much smaller area of morphospace than the placental taxa, with a significantly (p <0.01) smaller overall variance. The inclusion of fossil taxa did not significantly increase the variance of metatherian cranial shape. Fossil forms generally plotted close to or within the realm of their extant marsupial relatives. When the disparities of cranial regions were investigated separately, significant differences were observed between placentals and marsupials for the viscerocranial and oral region, but not for the neurocranial region. Conclusion: These results support the hypothesis of developmental constraint limiting the evolution of the marsupial skull, and further suggest that the marsupial viscerocranium as a whole is developmentally constrained, rather than just the early ossifying oral region.

High-density linkage mapping in a pine tree reveals a genomic region associated with inbreeding depression and provides clues to the extent and distribution of meiotic recombination

Emilie Chancerel — 2013-04-18T00:00:00Z

Background: The availability of a large EST resource and recent advances in high-throughput genotyping technology have made it possible to develop highly multiplexed SNP arrays for multi-objective genetic applications, including the construction of meiotic maps. Such approaches are particularly useful in species with a large genome size, precluding the use of whole-genome shotgun assembly with current technologies. Results: In this study, a 12 k-SNP genotyping array was developed for maritime pine from an extensive EST resource assembled into a unigene set. The offspring of three-generation outbred and inbred mapping pedigrees were then genotyped. The inbred pedigree consisted of a classical F2 population resulting from the selfing of a single inter-provenance (Landes x Corsica) hybrid tree, whereas the outbred pedigree (G2) resulted from a controlled cross of two intra-provenance (Landes x Landes) hybrid trees. This resulted in the generation of three linkage maps based on SNP markers: one from the parental genotype of the F2 population (1,131 markers in 1,708 cM), and one for each parent of the G2 population (1,015 and 1,110 markers in 1,447 and 1,425 cM for the female and male parents, respectively). A comparison of segregation patterns in the progeny obtained from the two types of mating (inbreeding and outbreeding) led to the identification of a chromosomal region carrying an embryo viability locus with a semi-lethal allele. Following selfing and segregation, zygote mortality resulted in a deficit of Corsican homozygous genotypes in the F2 population. This dataset was also used to study the extent and distribution of meiotic recombination along the length of the chromosomes, and the effect of sex and/or genetic background on recombination. The genetic background of trees in which meiotic recombination occurred was found to have a significant effect on the frequency of recombination. Furthermore, only a small proportion of the recombination hot- and cold-spots were common to all three genotypes, suggesting that the spatial pattern of recombination was genetically variable. Conclusion: This study led to the development of classical genomic tools for this ecologically and economically important species. It also identified a chromosomal region bearing a semi-lethal recessive allele and demonstrated the genetic variability of recombination rate over the genome.

Radial glial cells play a key role in echinoderm neural regeneration

Vladimir Mashanov — 2013-04-18T00:00:00Z

Background: Unlike the mammalian central nervous system (CNS), the CNS of echinoderms is capable of fast and efficient regeneration following injury and constitutes one of the most promising model systems that can provide important insights into evolution of the cellular and molecular events involved in neural repair in deuterostomes. So far, the cellular mechanisms of neural regeneration in echinoderm remained obscure. In this study we show that radial glial cells are the main source of new cells in the regenerating radial nerve cord in these animals. Results: We demonstrate that radial glial cells of the sea cucumber Holothuria glaberrima react to injury by dedifferentiation. Both glia and neurons undergo programmed cell death in the lesioned CNS, but it is the dedifferentiated glial subpopulation in the vicinity of the injury that accounts for the vast majority of cell divisions. Glial outgrowth leads to formation of a tubular scaffold at the growing tip, which is later populated by neural elements. Most importantly, radial glial cells themselves give rise to new neurons. At least some of the newly produced neurons survive for more than 4 months and express neuronal markers typical of the mature echinoderm CNS. Conclusions: A hypothesis is formulated that CNS regeneration via activation of radial glial cells may represent a common capacity of the Deuterostomia, which is not invoked spontaneously in higher vertebrates, whose adult CNS does not retain radial glial cells. Potential implications for biomedical research aimed at finding the cure for human CNS injuries are discussed.

Segment assembly, structure alignment and iterative simulation in protein structure prediction

Yang Zhang — 2013-04-15T00:00:00Z

No description available

Neurosensory transmission without a synapse: new perspectives on taste signaling

Sue Kinnamon — 2013-04-15T00:00:00Z

No description available