The evolution of a highly variable sex chromosome in Gehyra purpurascens (Gekkonidae)

A karyotypic survey of the gekkonid lizard Gehyra purpurascens revealed a distinctive sex chromosome system. G-banding showed that the Z Chromosome of males is derived from a tandem fusion of two acrocentric chromosomes of a presumed ancestral Gehyra with 2n=44. Through the application of G-; N- and C-banding, a total of six morphs of the W chromosome were identified. These differ by paracentric and pericentric inversions and, in one case, by a centric shift. The possible reasons for such extensive variation in the W chromosome are considered, and it is suggested that increased mutability of the W chromosome may be a causal factor. In contrast to earlier speculations, this example demonstrates that sex chromosomes can evolve without significant changes in the amount of C-band heterochromatin.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/47361/1/412_2004_Article_BF00292447.pd

Data from: Small RNAs from a big genome: the piRNA pathway and transposable elements in the salamander species Desmognathus fuscus

Most of the largest vertebrate genomes are found in salamanders, a clade of amphibians that includes 686 species. Salamander genomes range in size from 14 to 120 Gb, reflecting the accumulation of large numbers of transposable element (TE) sequences from all three TE classes. Although DNA loss rates are slow in salamanders relative to other vertebrates, high levels of TE insertion are also likely required to explain such high TE loads. Across the Tree of Life, novel TE insertions are suppressed by several pathways involving small RNA molecules. In most known animals, TE activity in the germline is primarily regulated by the Piwi-interacting RNA (piRNA) pathway. In this study, we test the hypothesis that salamanders’ unusually high TE loads reflect the loss of the ancestral piRNA-mediated TE-silencing machinery. We characterized the small RNA pool in the female and male adult gonads, testing for the presence of small RNA molecules that bear the characteristics of TE-targeting piRNAs. We also analyzed the amino acid sequences of piRNA pathway proteins from salamanders and other vertebrates, testing whether the overall patterns of sequence divergence are consistent with conserved pathway function across the vertebrate clade. Our results do not support the hypothesis of piRNA pathway loss; instead, they suggest that the piRNA pathway is expressed in salamanders. Given these results, we propose hypotheses to explain how the extraordinary TE loads in salamander genomes could have accumulated, despite the expression of TE-silencing machinery

Cytogenetic and Molecular Data Demonstrate that the Bryconinae (Ostariophysi, Bryconidae) Species from Southeastern Brazil Form a Phylogenetic and Phylogeographic Unit

<div><p><i>Brycon</i> spp. occur in Neotropical watersheds to the west and east of the Andes, and as they are sensitive to anthropogenic changes, many these species are endangered in southeastern Brazil. Coastal rivers in southeastern Brazil are characterized by the presence of relatively few freshwater fish species and high endemism of this fauna. The objective of this study was to examine whether <i>Brycon</i> spp. occurring in the coastal basins of southeastern Brazil are monophyletic, using cytogenetic data, mitochondrial, and nuclear molecular markers. All the species showed a diploid number of 50 chromosomes, a conserved number within the subfamily Bryconinae. However, the karyotypic formulas were unique to most species, including <i>Brycon devillei</i> (26m+22sm+2st), <i>Brycon ferox</i> (26m+12sm+12st), <i>Brycon insignis</i> (22m+20sm+8st), <i>Brycon opalinus</i>, and <i>Brycon vermelha</i> (24m+20sm+6st), indicating the prevalence of pericentric and paracentric inversions in the chromosomal evolution of these species. All of them had nucleolar organizer regions in the first pair of subtelocentric chromosomes and no equilocal distribution of heterochromatin in the first pair of chromosomes of the karyotype. These two features, not seen in any other <i>Brycon</i> spp. examined to date, indicate that Bryconinae species from the Brazilian southeastern coastal basins, including the monotypic genus <i>Henochilus</i>, are monophyletic. Also, this is the first study that reports NOR location and C-banding patterns as synapomorphies for a Neotropical fish species group. The monophyly was also supported by a phylogenetic analysis of <i>16S</i> rDNA (<i>16S</i>), cytochrome oxidase subunit I (<i>COI</i>), alpha-myosin (<i>MYH6</i>) genes and <i>S72</i> intron molecular data. Our results partially corroborate the “<i>Brycon acuminatus</i>” group proposed by Howes in 1982: our proposed clade keeps <i>B</i>. <i>devillei</i>, <i>B</i>. <i>ferox</i>, and <i>B</i>. <i>insignis;</i> but it also includes <i>B</i>. <i>opalinus</i>, <i>B</i>. <i>vermelha</i>, and <i>H</i>. <i>weatlandii</i> whereas it excludes <i>B</i>. <i>nattereri</i>. The phylogeographic unit formed by Bryconinae species in southeastern Brazil reflects the long and isolated paleohydrological history of these coastal basins relative to the continental watersheds.</p></div

Rapid prototyping-assisted maxillofacial reconstruction

© 2015 Informa UK, Ltd. Rapid prototyping (RP) technologies have found many uses in dentistry, and especially oral and maxillofacial surgery, due to its ability to promote product development while at the same time reducing cost and depositing a part of any degree of complexity theoretically. This paper provides an overview of RP technologies for maxillofacial reconstruction covering both fundamentals and applications of the technologies. Key fundamentals of RP technologies involving the history, characteristics, and principles are reviewed. A number of RP applications to the main fields of oral and maxillofacial surgery, including restoration of maxillofacial deformities and defects, reduction of functional bone tissues, correction of dento-maxillofacial deformities, and fabrication of maxillofacial prostheses, are discussed. The most remarkable challenges for development of RP-assisted maxillofacial surgery and promising solutions are also elaborated