Página 7 dos resultados de 157 itens digitais encontrados em 0.002 segundos

Platypus Pou5f1 reveals the first steps in the evolution of trophectoderm differentiation and pluripotency in mammals

Niwa, H.; Sekita, Y.; Tsend-Ayush, E.; Grutzner, F.
Fonte: Blackwell Publishing Inc Publicador: Blackwell Publishing Inc
Tipo: Artigo de Revista Científica
Publicado em //2008 EN
Relevância na Pesquisa
16.55%
SUMMARY Uterine nourishment of embryos by the placenta is a key feature of mammals. Although a variety of placenta types exist, they are all derived from the trophectoderm (TE) cell layer of the developing embryo. Egg-laying mammals (platypus and echidnas) are distinguished by a very short intrauterine embryo development, in which a simple placenta forms from TE-like cells. The Pou5f1 gene encodes a class V POU family transcription factor Oct3/4. In mice, Oct3/4 together with the highly conserved caudal-related homeobox transcription factor Cdx2, determines TE fate in pre-implantation development. In contrast to Cdx2, Pou5f1 has only been identified in eutherian mammals and marsupials, whereas, in other vertebrates, pou2 is considered to be the Pou5f1 ortholog. Here, we show that platypus and opossum genomes contain a Pou5f1 and pou2 homolog, pou2-related, indicating that these two genes are paralogues and arose by gene duplication in early mammalian evolution. In a complementation assay, we found that platypus or human Pou5f1, but not opossum or zebrafish pou2, restores self-renewal in Pou5f1-null mouse ES cells, showing that platypus possess a fully functional Pou5f1 gene. Interestingly, we discovered that parts of one of the conserved regions (CR4) is missing from the platypus Pou5f1 promoter...

Higher-order genome organization in platypus and chicken sperm and repositioning of sex chromosomes during mammalian evolution

Tsend-Ayush, E.; Dodge, N.; Mohr, J.; Casey, A.; Himmelbauer, H.; Kremitzki, C.; Schatzkamer, K.; Graves, T.; Warren, W.; Grutzner, F.
Fonte: Springer Publicador: Springer
Tipo: Artigo de Revista Científica
Publicado em //2009 EN
Relevância na Pesquisa
16.55%
In mammals, chromosomes occupy defined positions in sperm, whereas previous work in chicken showed random chromosome distribution. Monotremes (platypus and echidnas) are the most basal group of living mammals. They have elongated sperm like chicken and a complex sex chromosome system with homology to chicken sex chromosomes. We used platypus and chicken genomic clones to investigate genome organization in sperm. In chicken sperm, about half of the chromosomes investigated are organized non-randomly, whereas in platypus chromosome organization in sperm is almost entirely non-random. The use of genomic clones allowed us to determine chromosome orientation and chromatin compaction in sperm. We found that in both species chromosomes maintain orientation of chromosomes in sperm independent of random or non-random positioning along the sperm nucleus. The distance of loci correlated with the total length of sperm nuclei, suggesting that chromatin extension depends on sperm elongation. In platypus, most sex chromosomes cluster in the posterior region of the sperm nucleus, presumably the result of postmeiotic association of sex chromosomes. Chicken and platypus autosomes sharing homology with the human X chromosome located centrally in both species suggesting that this is the ancestral position. This suggests that in some therian mammals a more anterior position of the X chromosome has evolved independently.; Enkhjargal Tsend-Ayush...

The enigma of the platypus genome

Warren, W.; Grutzner, F.
Fonte: C S I R O Publishing Publicador: C S I R O Publishing
Tipo: Artigo de Revista Científica
Publicado em //2009 EN
Relevância na Pesquisa
16.55%
Over two centuries after the first platypus specimen stirred the scientific community in Europe, the whole-genome sequence of the duck-billed platypus has been completed and is publicly available. After publication of eutherian and marsupial genomes, this is the first genome of a monotreme filling an important evolutionary gap between the divergence of birds more that 300 million years ago and marsupials more than 140 million years ago. Monotremes represent the most basal surviving branch of mammals and the platypus genome sequence allows unprecedented insights into the evolution of mammals and the fascinating biology of the egg-laying mammals. Here, we discuss some of the key findings of the analysis of the platypus genome and point to new findings and future research directions, which illustrate the broad impact of the platypus genome project for understanding monotreme biology and mammalian genome evolution.; Wesley C. Warren and Frank Grützner; © CSIRO 2009

Analysis of SINE and LINE repeat content of Y chromosomes in the platypus, Ornithorhynchus anatinus

Kortschak, R.; Tsend-Ayush, E.; Grutzner, F.
Fonte: C S I R O Publishing Publicador: C S I R O Publishing
Tipo: Artigo de Revista Científica
Publicado em //2009 EN
Relevância na Pesquisa
16.55%
Monotremes feature an extraordinary sex-chromosome system that consists of five X and five Y chromosomes in males. These sex chromosomes share homology with bird sex chromosomes but no homology with the therian X. The genome of a female platypus was recently completed, providing unique insights into sequence and gene content of autosomes and X chromosomes, but no Y-specific sequence has so far been analysed. Here we report the isolation, sequencing and analysis of approximately 700 kb of sequence of the non-recombining regions of Y2, Y3 and Y5, which revealed differences in base composition and repeat content between autosomes and sex chromosomes, and within the sex chromosomes themselves. This provides the first insights into repeat content of Y chromosomes in platypus, which overall show similar patterns of repeat composition to Y chromosomes in other species. Interestingly, we also observed differences between the various Y chromosomes, and in combination with timing and activity patterns we provide an approach that can be used to examine the evolutionary history of the platypus sex-chromosome chain.; Kortschak, RD; Tsend-Ayush, E. and Grutzner, F.

Platypus chain reaction: directional and ordered meiotic pairing of the multiple sex chromosome chain in Ornithorhynchus anatinus

Daish, T.; Casey, A.; Grutzner, F.
Fonte: C S I R O Publishing Publicador: C S I R O Publishing
Tipo: Artigo de Revista Científica
Publicado em //2009 EN
Relevância na Pesquisa
16.55%
Monotremes are phylogenetically and phenotypically unique animals with an unusually complex sex chromosome system that is composed of ten chromosomes in platypus and nine in echidna. These chromosomes are alternately linked (X1Y1, X2Y2, ...) at meiosis via pseudoautosomal regions and segregate to form spermatozoa containing either X or Y chromosomes. The physical and epigenetic mechanisms involved in pairing and assembly of the complex sex chromosome chain in early meiotic prophase I are completely unknown. We have analysed the pairing dynamics of specific sex chromosome pseudoautosomal regions in platypus spermatocytes during prophase of meiosis I. Our data show a highly coordinated pairing process that begins at the terminal Y5 chromosome and completes with the union of sex chromosomes X1Y1. The consistency of this ordered assembly of the chain is remarkable and raises questions about the mechanisms and factors that regulate the differential pairing of sex chromosomes and how this relates to potential meiotic silencing mechanisms and alternate segregation.; Tasman Daish, Aaron Casey and Frank Grützner; © CSIRO 2009

The evolutionary history of testicular externalization and the origin of the scrotum

Kleisner, K.; Ivell, R.; Flegr, J.
Fonte: Indian Academy Sciences Publicador: Indian Academy Sciences
Tipo: Artigo de Revista Científica
Publicado em //2010 EN
Relevância na Pesquisa
16.55%
This paper re-examines the evolution of the scrotum and testicular descent in the context of the recent phylogeny of mammals. The adaptive significance of testicular descent and scrotality is briefly discussed. We mapped four character states reflecting the position of testes and presence of scrotum onto recent mammalian phylogeny. Our results are interpreted as follows: as to the presence of testicondy in Monotremata and most of Atlantogenata, which represent the basal group of all eutherians, we argue that primary testicondy represents a plesiomorphic condition for Eutheria as well as for all mammals. This is in opposition to the previous hypothesis of Werdelin and Nilsonne that the scrotum may have evolved before the origin of mammals and then repeatedly disappeared in many groups including monotremes. We suggest that the scrotum evolved at least twice during the evolutionary history of mammals, within Marsupialia and Boreoeutheria, and has subsequently been lost by many groups; this trend is especially strong in Laurasiatheria. We suggest that the recent diversity in testicular position within mammals is the result of multiple selection pressures stemming from the need to provide conditions suitable for sperm development and storage...

Were early Tertiary monotremes really all aquatic? Inferring paleobiology and phylogeny from a depauperate fossil record

Camens, Aaron Bruce
Fonte: National Academy of Sciences Publicador: National Academy of Sciences
Tipo: Artigo de Revista Científica
Publicado em //2010 EN
Relevância na Pesquisa
16.55%
Aaron B. Camens

Reply to Camens: How recently did modern monotremes diversify?

Phillips, M.; Bennett, T.; Lee, M.
Fonte: Natl Acad Sciences Publicador: Natl Acad Sciences
Tipo: Artigo de Revista Científica
Publicado em //2010 EN
Relevância na Pesquisa
16.55%
Matthew J. Phillips, T. H. Bennett and Michael S. Y. Lee

Mechanisms and evolutionary patterns of mammalian and avian dosage compensation

Julien, P.; Brawand, D.; Soumillon, M.; Necsulea, A.; Liechti, A.; Schutz, F.; Daish, T.; Grutzner, F.; Kaessmann, H.
Fonte: Public Library of Science Publicador: Public Library of Science
Tipo: Artigo de Revista Científica
Publicado em //2012 EN
Relevância na Pesquisa
16.55%
As a result of sex chromosome differentiation from ancestral autosomes, male mammalian cells only contain one X chromosome. It has long been hypothesized that X-linked gene expression levels have become doubled in males to restore the original transcriptional output, and that the resulting X overexpression in females then drove the evolution of X inactivation (XCI). However, this model has never been directly tested and patterns and mechanisms of dosage compensation across different mammals and birds generally remain little understood. Here we trace the evolution of dosage compensation using extensive transcriptome data from males and females representing all major mammalian lineages and birds. Our analyses suggest that the X has become globally upregulated in marsupials, whereas we do not detect a global upregulation of this chromosome in placental mammals. However, we find that a subset of autosomal genes interacting with X-linked genes have become downregulated in placentals upon the emergence of sex chromosomes. Thus, different driving forces may underlie the evolution of XCI and the highly efficient equilibration of X expression levels between the sexes observed for both of these lineages. In the egg-laying monotremes and birds...

A first look at monotreme meiotic recombination.

Horan, Sonia
Fonte: Universidade de Adelaide Publicador: Universidade de Adelaide
Tipo: Tese de Doutorado
Publicado em //2012
Relevância na Pesquisa
16.55%
Recombination is a critical event in meiosis required for proper chromosome segregation; however, despite its importance, crossovers have not yet been analysed in egg-laying mammals, representing an extant species from the most basal of the contemporary mammalian lineage. The platypus is a unique species in that it has a complex system of ten sex chromosomes that form a chain in meiosis, and the segregation of this chain raises many questions regarding the state of meiotic recombination among chain members. This study aimed to set a foundation for recombination studies in the platypus. 15 genes essential for crossover formation were analysed; while most of these genes showed generally high levels of conservation, surprisingly it was found that Mei4 and Rec114 are not expressed during platypus meiosis. This raises several questions about the platypus double-strand break induction mechanism in which these genes have an essential function in other mammals. Furthermore, characterisation of the crossover hotspot-determining protein, Prdm9, shows that the platypus protein differs significantly from the Prdm9 of eutherians, suggesting that the gene underwent rapid evolution after the divergence of monotremes nearly 200 Million years ago. This study also aimed to examine the distribution of crossovers in meiotic cells using Mlh1 as a marker for crossover events. Despite conservation of the protein and expression and some specific staining overall...

Insights into the evolution of mammalian telomerase: Platypus TERT shares similarities with genes of birds and other reptiles and localizes on sex chromosomes

Hrdlickova, R.; Nehyba, J.; Lim, S.; Grutzner, F.; Bose, H.
Fonte: BioMed Central Ltd. Publicador: BioMed Central Ltd.
Tipo: Artigo de Revista Científica
Publicado em //2012 EN
Relevância na Pesquisa
16.55%
Background The TERT gene encodes the catalytic subunit of the telomerase complex and is responsible for maintaining telomere length. Vertebrate telomerase has been studied in eutherian mammals, fish, and the chicken, but less attention has been paid to other vertebrates. The platypus occupies an important evolutionary position, providing unique insight into the evolution of mammalian genes. We report the cloning of a platypus TERT (OanTERT) ortholog, and provide a comparison with genes of other vertebrates. Results The OanTERT encodes a protein with a high sequence similarity to marsupial TERT and avian TERT. Like the TERT of sauropsids and marsupials, as well as that of sharks and echinoderms, OanTERT contains extended variable linkers in the N-terminal region suggesting that they were present already in basal vertebrates and lost independently in rayfinned fish and eutherian mammals. Several alternatively spliced OanTERT variants structurally similar to avian TERT variants were identified. Telomerase activity is expressed in all platypus tissues like that of cold-blooded animals and murine rodents. OanTERT was localized on pseudoautosomal regions of sex chromosomes X3/Y2, expanding the homology between human chromosome 5 and platypus sex chromosomes. Synteny analysis suggests that TERT co-localized with sex-linked genes in the last common mammalian ancestor. Interestingly...

Widespread horizontal transfer of retrotransposons

Walsh, A.; Kortschak, R.; Gardner, M.; Bertozzi, T.; Adelson, D.
Fonte: Natl Acad Sciences Publicador: Natl Acad Sciences
Tipo: Artigo de Revista Científica
Publicado em //2013 EN
Relevância na Pesquisa
16.55%
In higher organisms such as vertebrates, it is generally believed that lateral transfer of genetic information does not readily occur, with the exception of retroviral infection. However, horizontal transfer (HT) of protein coding repetitive elements is the simplest way to explain the patchy distribution of BovB, a long interspersed element (LINE) about 3.2 kb long, that has been found in ruminants, marsupials, squamates, monotremes, and African mammals. BovB sequences are a major component of some of these genomes. Here we show that HT of BovB is significantly more widespread than believed, and we demonstrate the existence of two plausible arthropod vectors, specifically reptile ticks. A phylogenetic tree built from BovB sequences from species in all of these groups does not conform to expected evolutionary relationships of the species, and our analysis indicates that at least nine HT events are required to explain the observed topology. Our results provide compelling evidence for HT of genetic material that has transformed vertebrate genomes.; Ali Morton Walsh, R. Daniel Kortschak, Michael G. Gardner, Terry Bertozzi, and David L. Adelson

Resolution and evolution of the duck-billed platypus karyotype with an X1Y1X2Y2X3Y3X4Y4X5Y5 male sex chromosome constitution

Rens, W.; Grutzner, F.; O'Brien, P.; Fairclough, H.; Graves, J.; Ferguson-Smith, M.
Fonte: Natl Acad Sciences Publicador: Natl Acad Sciences
Tipo: Artigo de Revista Científica
Publicado em //2004 EN
Relevância na Pesquisa
16.55%
The platypus (2n = 52) has a complex karyotype that has been controversial over the last three decades. The presence of unpaired chromosomes and an unknown sex-determining system especially has defied attempts at conventional analysis. This article reports on the preparation of chromosome-specific probes from flow-sorted chromosomes and their application in the identification and classification of all platypus chromosomes. This work reveals that the male karyotype has 21 pairs of chromosomes and 10 unpaired chromosomes (E1-E10), which are linked by short regions of homology to form a multivalent chain in meiosis. The female karyotype differs in that five of these unpaired elements (E1, E3, E5, E7, and E9) are each present in duplicate, whereas the remaining five unpaired elements (E2, E4, E6, E8, and E10) are absent. This finding indicates that sex is determined by the alternate segregation of the chain of 10 during spermatogenesis so that equal numbers of sperm bear either one of the two groups of five elements, i.e., five X and five Y chromosomes. Chromosome painting reveals that these X and Y chromosomes contain pairing (XY shared) and differential (X- or Y-specific) segments. Y differential regions must contain male-determining genes...

A Handbook of New Guinea's Marsupials and Monotremes

Menzies, J.
Fonte: University of Papua New Guinea Press; New Guinea Publicador: University of Papua New Guinea Press; New Guinea
Tipo: Livro
Publicado em //2011 EN
Relevância na Pesquisa
16.55%
James Menzies; 2nd edition

Platypus globin genes and flanking loci suggest a new insertional model for beta-globin evolution in birds and mammals

Patel, V.; Cooper, S.; Deakin, J.; Fulton, B.; Graves, T.; Warren, W.; Wilson, R.; Graves, J.
Fonte: BioMed Central Ltd. Publicador: BioMed Central Ltd.
Tipo: Artigo de Revista Científica
Publicado em //2008 EN
Relevância na Pesquisa
16.55%
Background: Vertebrate alpha (α)- and beta (β)-globin gene families exemplify the way in which genomes evolve to produce functional complexity. From tandem duplication of a single globin locus, the α- and β-globin clusters expanded, and then were separated onto different chromosomes. The previous finding of a fossil β-globin gene (ω) in the marsupial α-cluster, however, suggested that duplication of the α-β cluster onto two chromosomes, followed by lineage-specific gene loss and duplication, produced paralogous α- and β-globin clusters in birds and mammals. Here we analyse genomic data from an egg-laying monotreme mammal, the platypus (Ornithorhynchus anatinus), to explore haemoglobin evolution at the stem of the mammalian radiation. Results: The platypus α-globin cluster (chromosome 21) contains embryonic and adult α- globin genes, a β-like ω-globin gene, and the GBY globin gene with homology to cytoglobin, arranged as 5'-ζ-ζ'-αD-α3-α2-α1-ω-GBY-3'. The platypus β-globin cluster (chromosome 2) contains single embryonic and adult globin genes arranged as 5'-ε-β-3'. Surprisingly, all of these globin genes were expressed in some adult tissues. Comparison of flanking sequences revealed that all jawed vertebrate α-globin clusters are flanked by MPG-C16orf35 and LUC7L...

Platypus globin genes and flanking loci suggest a new insertional model for beta-globin evolution in birds and mammals

Patel, Vidushi; Deakin, Janine; Graves, Jennifer; Cooper, Steven; Fulton, Bob; Graves, Tina; Warren, Wesley; Wilson, Richard K
Fonte: Universidade Nacional da Austrália Publicador: Universidade Nacional da Austrália
Tipo: Artigo de Revista Científica Formato: 22 pages
Relevância na Pesquisa
16.55%
BACKGROUND: Vertebrate alpha (α)- and beta (β)-globin gene families exemplify the way in which genomes evolve to produce functional complexity. From tandem duplication of a single globin locus, the α- and β-globin clusters expanded, and then were separated onto different chromosomes. The previous finding of a fossil β-globin gene (ω) in the marsupial α-cluster, however, suggested that duplication of the α-β cluster onto two chromosomes, followed by lineage-specific gene loss and duplication, produced paralogous α- and β-globin clusters in birds and mammals. Here we analyse genomic data from an egg-laying monotreme mammal, the platypus (Ornithorhynchus anatinus), to explore haemoglobin evolution at the stem of the mammalian radiation. RESULTS: The platypus α-globin cluster (chromosome 21) contains embryonic and adult α- globin genes, a β-like ω-globin gene, and the GBY globin gene with homology to cytoglobin, arranged as 5'-ζ-ζ'-αD-α3-α2-α1-ω-GBY-3'. The platypus β-globin cluster (chromosome 2) contains single embryonic and adult globin genes arranged as 5'-ε-β-3'. Surprisingly, all of these globin genes were expressed in some adult tissues. Comparison of flanking sequences revealed that all jawed vertebrate α-globin clusters are flanked by MPG-C16orf35 and LUC7L...

The multiple sex chromosomes of platypus and echidna are not completely identical and several share homology with the avian Z

Rens, Willem; O'Brien, Patricia CM; Grützner, Frank; Clarke, Oliver; Graphodatskaya, Daria; Tsend-Ayush, Enkhjargal; Trifonov, Vladimir A; Skelton, Helen; Wallis, Mary C; Johnston, Steve; Veyrunes, Frederic; Graves, Jennifer AM; Ferguson-Smith, Malcolm A
Fonte: BioMed Central Publicador: BioMed Central
Tipo: Artigo de Revista Científica
EN
Relevância na Pesquisa
16.55%
A comparative study of the karyotype of the short-beaked echidna shows that monotremes appear to have a unique XY sex chromosome system that shares some homology with the avian Z.

On the homology of the alisphenoid.

Presely, R; Steel, F L
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /07/1976 EN
Relevância na Pesquisa
16.55%
The relationships of the elements of the cavum epiptericum in a hypothetical primitive mammalian precursor are reconstructed, and these are analysed in relation to the development of recent mammals, especially the fruit bat Nyctinomus johorensis. The alisphenoid in mammals is part cartilage bone, part membrane bone. The mammalian homologue of the primitive reptilian processus ascendens appears to be internal to the maxillary nerve. If so, then the 'lamina ascendens', that portion of the alisphenoid of mammals which lies between maxillary and mandibular nerves, cannot be a true processus ascendens but must be neomorphic. It is suggested that the mammalian lamina ascendens arose from an upgrowth of the root of the quadrate ramus of the epipterygoid in cynodonts, separating foramen rotundum from foramen ovale. In Ditremata the alisphenoid is completed by an element of membrane bone; this, it is suggested here, originated as the anterior lamina of the periotic in cynodonts, which is retained in monotremes. It is suggested that the alicochlear commissure of mammals originated as the later flange of the periotic in cynodonts.

Comparative studies of `bile salts'. 16. Bile salts of monotremes and observations on glycine conjugation*

Bridgwater, R. J.; Haslewood, G. A. D.; Tammar, A. R.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /11/1962 EN
Relevância na Pesquisa
16.55%

Ubiquitous mammalian-wide interspersed repeats (MIRs) are molecular fossils from the mesozoic era.

Jurka, J; Zietkiewicz, E; Labuda, D
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em 11/01/1995 EN
Relevância na Pesquisa
16.55%
Short interspersed elements (SINEs) are ubiquitous in mammalian genomes. Remarkable variety of these repeats among placental orders indicates that most of them amplified in each lineage independently, following mammalian radiation. Here, we present an ancient family of repeats, whose sequence divergence and common occurrence among placental mammals, marsupials and monotremes indicate their amplification during the Mesozoic era. They are called MIRs for abundant Mammalian-wide Interspersed Repeats. With approximately 120,000 copies still detectable in the human genome (0.2-0.3% DNA), MIRs represent a 'fossilized' record of a major genetic event preceding the radiation of placental orders.