Early origins of the X and Y chromosomes: lessons from tilapia

Differentiated sex chromosome pairs in diverse species display certain common characteristics, normally comprising one largely heterochromatic genetically inactive chromosome and one euchromatic genetically active chromosome (e.g. the mammalian Y and X respectively). It is widely accepted that dimorphic sex chromosomes evolved from homologous pairs of autosomes. Although the exact mechanisms through which the pair diverged are not fully understood, an initial suppression of recombination in the sex-determining region is required by all of the major theories. Here we address the question of the mechanism by which this initial suppression of recombination occurs. Our model postulates that the stochastic, de novo accumulation of heterochromatin in the sex determining region can delay pairing of the sex chromosomes in meiosis, resulting in a decrease in recombination. Data to support this model is presented from the cichlid fish, Oreochromis niloticus. Although such a decrease would in most circumstances be evolutionarily disadvantageous, if the region concerned included the major sex determining gene and other gene(s) with sex-specific functions, then this would be selectively advantageous and could trigger the process(es) which, ultimately, lead to the differentiation of the sex chromosomes

Diversity and distribution patterns in high southern latitude sponges

Sponges play a key role in Antarctic marine benthic community structure and dynamics and are often a dominant component of many Southern Ocean benthic communities. Understanding the drivers of sponge distribution in Antarctica enables us to understand many of general benthic biodiversity patterns in the region. The sponges of the Antarctic and neighbouring oceanographic regions were assessed for species richness and biogeographic patterns using over 8,800 distribution records. Species-rich regions include the Antarctic Peninsula, South Shetland Islands, South Georgia, Eastern Weddell Sea, Kerguelen Plateau, Falkland Islands and north New Zealand. Sampling intensity varied greatly within the study area, with sampling hotspots found at the Antarctic Peninsula, South Georgia, north New Zealand and Tierra del Fuego, with limited sampling in the Bellingshausen and Amundsen seas in the Southern Ocean. In contrast to previous studies we found that eurybathy and circumpolar distributions are important but not dominant characteristics in Antarctic sponges. Overall Antarctic sponge species endemism is ,43%, with a higher level for the class Hexactinellida (68%). Endemism levels are lower than previous estimates, but still indicate the importance of the Polar Front in isolating the Southern Ocean fauna. Nineteen distinct sponge distribution patterns were found, ranging from regional endemics to cosmopolitan species. A single, distinct Antarctic demosponge fauna is found to encompass all areas within the Polar Front, and the sub-Antarctic regions of the Kerguelen Plateau and Macquarie Island. Biogeographical analyses indicate stronger faunal links between Antarctica and South America, with little evidence of links between Antarctica and South Africa, Southern Australia or New Zealand. We conclude that the biogeographic and species distribution patterns observed are largely driven by the Antarctic Circumpolar Current and the timing of past continent connectivity

Mapping neurobiological alterations in obsessive-compulsive disorder

This article will explore recent studies that have identified alterations in brain regions in individuals with obsessive–compulsive disorder (OCD). Specifically, alterations have been found in the cortical surface anatomy, the white matter, the gray matter, the cerebellum, the olfactory-processing structures, the temporal lobe, the prefrontal cortex, and the amygdala. Although some emerging data implicate these brain regions in OCD, the cortico–striatal–thalamic–cortical circuitry remains the prime focus of research. This article will also give an overview of studies that have found different symptom dimensions in individuals with OCD to have distinct neural correlates

Anion recognition and anion-mediated self-assembly with thiourea-functionalised fused [3]polynorbornyl frameworks

Three conformationally preorganised host molecules based on the [3]polynorbornyl framework and incorporating di-urea receptors were synthesised and their interaction with a series of anions investigated by 1H NMR spectroscopy. A high affinity of each host molecule for dihydrogenphosphate (H2PO4&ndash;) and dihydrogenpyrophosphate (H2P2O72&ndash;) was identified. In addition to binding to the urea receptors of the host molecules, evidence for an interaction involving the non-polar C&ndash;H groups within the binding cavity of the framework and guest anions was also discovered. Furthermore, an unusual 2 : 1 host-to-anion stoichiometry was indicated when binding H2P2O72&ndash;, and a model for the anion-mediated self-assembly of this complex species is proposed.<br /