To explore the origins and consequences of tetraploidy in the African clawed frog, we sequenced the Xenopus laevis genome and compared it to the related diploid X. tropicalis genome. We demonstrate the allotetraploid origin of X. laevis by partitioning its genome into two homeologous subgenomes, marked by distinct families of “fossil” transposable elements. Based on the activity of these elements and the age of hundreds of unitary pseudogenes, we estimate that the two diploid progenitor species diverged ~34 million years ago (Mya) and combined to form an allotetraploid ~17–18 Mya. 56% of all genes are retained in two homeologous copies. Protein function, gene expression, and the amount of flanking conserved sequence all correlate with retention rates. The subgenomes have evolved asymmetrically, with one chromosome set more often preserving the ancestral state and the other experiencing more gene loss, deletion, rearrangement, and reduced gene expression.
The western clawed frog Xenopus tropicalis is an important model for vertebrate development that combines experimental advantages of the African clawed frog Xenopus laevis with more tractable genetics. Here we present a draft genome sequence assembly of X. tropicalis. This genome encodes over 20,000 protein-coding genes, including orthologs of at least 1,700 human disease genes. Over a million expressed sequence tags validated the annotation. More than one-third of the genome consists of transposable elements, with unusually prevalent DNA transposons. Like other tetrapods, the genome contains gene deserts enriched for conserved non-coding elements. The genome exhibits remarkable shared synteny with human and chicken over major parts of large chromosomes, broken by lineage-specific chromosome fusions and fissions, mainly in the mammalian lineage.
Since the last World Symposium on Pulmonary Hypertension in 2008, we have witnessed numerous and exciting developments in chronic thromboembolic pulmonary hypertension (CTEPH). Emerging clinical data and advances in technology have led to reinforcing and updated guidance on diagnostic approaches to pulmonary hypertension, guidelines that we hope will lead to better recognition and more timely diagnosis of CTEPH. We have new data on treatment practices across international boundaries as well as long-term outcomes for CTEPH patients treated with or without pulmonary endarterectomy. Furthermore, we have expanded data on alternative treatment options for select CTEPH patients, including data from multiple clinical trials of medical therapy, including 1 recent pivotal trial, and compelling case series of percutaneous pulmonary angioplasty. Lastly, we have garnered more experience, and on a larger international scale, with pulmonary endarterectomy, which is the treatment of choice for operable CTEPH. This report overviews and highlights these important interval developments as deliberated among our task force of CTEPH experts and presented at the 2013 World Symposium on Pulmonary Hypertension in Nice, France.
After the vertebrate lens is induced from head ectoderm, lens-specific genes are expressed. Transcriptional regulation of the lens-specific alphaA-crystallin gene is controlled by an enhancer element, alphaCE2. A gene encoding an alphaCE2-binding protein, L-maf(lens-specific maf), was isolated. L-maf expression is initiated in the lens placode and is restricted to lens cells. The gene product L-Maf regulates the expression of multiple genes expressed in the lens, and ectopic expression of this transcription factor converts chick embryonic ectodermal cells and cultured cells into lens fibers. Thus, vertebrate lens induction and differentiation can be triggered by the activation of L-Maf.
To elucidate the regulatory mechanisms underlying lens development, we searched for members of the large Maf family, which are expressed in the mouse lens, and found three, c-Maf, MafB, and Nrl. Of these, the earliest factor expressed in the lens was c-Maf. The expression of c-Maf was most prominent in lens fiber cells and persisted throughout lens development. To examine the functional contribution of c-Maf to lens development, we isolated genomic clones encompassing the murine c-maf gene and carried out its targeted disruption. Insertion of the -galactosidase (lacZ) gene into the c-maf locus allowed visualization of c-Maf accumulation in heterozygous mutant mice by staining for LacZ activity. Homozygous mutant embryos and newborns lacked normal lenses. Histological examination of these mice revealed defective differentiation of lens fiber cells. The expression of crystallin genes was severely impaired in the c-maf-null mutant mouse lens. These results demonstrate that c-Maf is an indispensable regulator of lens differentiation during murine development.Lens development commences in the 9.5-day-old (e9.5) mouse embryo by invagination of the lens placode to form lens pits on either side of the prospective forebrain (1, 2). Subsequently at e10.5, the lens pit forms a lens vesicle, where embryonic ectodermal cells differentiate into primary lens fiber cells. By e13.0, the primary posterior lens fiber cells grow into the lumen to eventually fill the lens vesicle. The anterior cells of the vesicle become epithelial cells and constitute the lens germinal epithelium; secondary fiber cells then differentiate from the epithelial cells after this stage. This arrangement persists throughout the lifetime of the animal, as new lens fibers are continuously regenerated (3).Differentiation of the lens involves biosynthesis of a group of fibrous lens-specific proteins called crystallins, which constitute 80 -90% of the soluble protein of the lens (4 -6). The regulation of the crystallin genes has been characterized extensively (7-10), and an enhancer for the chicken ␣A-crystallin gene has been identified (11,12). Biochemical analyses of the core region of this enhancer revealed key interacting transcription factors (13,14). Of the cis elements identified in the enhancer, the ␣CE2 sequence, which shares high similarity with the Maf responsive element (MARE 1 (15)), is crucial for its transcriptional activity. MARE-related consensus sequences have also been found in the regulatory regions of other lensspecific genes (12).Recently a new transcription factor, L-Maf, which can interact with the ␣CE2 enhancer element, was isolated from chicken lens (13). L-Maf is a member of the large Maf oncoprotein/ transcription factor family (16 -18). The Maf family factors contain a basic leucine zipper domain and bind to MARE either as homodimers or as heterodimers with other basic leucine zipper transcription factors (19). L-Maf regulates the expression of multiple lens-specific genes, and its forced expression can convert primary chick embry...
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