Página 1 dos resultados de 86 itens digitais encontrados em 0.001 segundos

Identification of N-acetyl-4-O-acetylneuraminyl-lactose in echidna milk

Messer, Michael
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /05/1974 EN
Relevância na Pesquisa
27.57%
The identity of a novel form of sialyl-lactose found in milk of the echidna (Tachyglossus aculeatus) was investigated. The sialyl-lactose yielded equimolar amounts of N-acetylneuraminic acid and lactose during mild acid hydrolysis but was resistant to the action of a bacterial neuraminidase. A viral neuraminidase hydrolysed it to lactose plus a form of sialic acid that reacted positively with thiobarbituric acid reagent but whose chromatographic mobility was greater than that of N-acetylneuraminic acid. Treatment with alkali converted the sialyl-lactose into a substance with the same chromatographic mobility as N-acetylneuraminyl-(2→3)-lactose and made it susceptible to the action of bacterial neuraminidase. The sialyl-lactose contained one mol of ester (identified as acetyl), and released one mol of formaldehyde during periodate oxidation, per mol of sialic acid. It did not contain N-glycollylneuraminic acid. These results indicate that the sialyl-lactose is N-acetyl-4-O-acetylneuraminyl-(2→3)-lactose. Echidna milk contained, in addition, a small amount of N-acetylneuraminyl-(2→3)-lactose.

Ultrastructure of the ductus epididymidis of the echidna, Tachyglossus aculeatus.

Djakiew, D; Jones, R C
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /10/1982 EN
Relevância na Pesquisa
27.76%
It is concluded that the ductus epididymidis of the echidna is divided into only two structurally distinct segments which are each homogeneous along their length. The initial segment in the echidna is structurally very similar to the initial segment proper in the epididymis of all other mammals which have been studied, whereas the terminal segment is structurally quite different from the terminal segment in other mammals. The terminal segment in the echidna is involved in considerable apocrine secretion of highly membranous material. The secretions gradually degenerate and occupy a large proportion of the lumen of the duct.

Responses of electroreceptors in the snout of the echidna.

Gregory, J E; Iggo, A; McIntyre, A K; Proske, U
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /07/1989 EN
Relevância na Pesquisa
27.76%
1. This is a report of experiments which provide evidence in support of the existence of an electric sense in the echidna, or spiny anteater Tachyglossus aculeatus. It is the first known example of electroreception in a terrestrial animal. 2. In each of four animals anaesthetized with alpha-chloralose, afferent responses were recorded in dissected filaments of the infraorbital branch of the trigeminal nerve which supplies skin of the upper jaw. Recordings were obtained from a total of forty-seven units identified as electroreceptors, by their responses to weak voltage pulses using focal stimulation of the moist skin surface. 3. In the absence of a stimulus, some receptors had an irregular resting discharge; others were silent. The receptive field for each receptor consisted of a discrete spot. Receptive fields were restricted to the tip of the snout. Cathodal stimulation over the receptive spot was excitatory for the duration of an applied voltage pulse. Reversal of stimulus polarity silenced any on-going activity and was followed by a post-anodal rebound excitation. 4. Receptor threshold was best measured not in air but with the snout immersed in tap water. An electric field was applied between a pair of large plate electrodes on either side of the snout. Threshold for thirty receptors lay in the range 1.8-73 mV cm-1. Measurements of response latency and of conduction path length gave estimates of axonal conduction velocities for the afferent fibres of 10-18 m Receptors responded to sinusoidally changing voltage gradients over the range 0.5-200 Hz with a maximum sensitivity at 20 Hz. 5. In one experiment a receptor site was marked with fine pins. Serial sections of the piece of underlying skin revealed a large mucus-secreting gland at the marked spot. Similar glands in skin of the platypus have previously been shown to be the sites of electroreceptors. 6. In a behavioural experiment an echidna was trained to choose between two identical tap water-filled troughs...

7S immunoglobulins of a monotreme, the Echidna Tachyglossus aculeatus: two distinct isotypes which bind A protein of Staphylococcus aureus

Marchalonis, J. J.; Atwell, J. L.; Goding, J. W.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /01/1978 EN
Relevância na Pesquisa
27.9%
7S immunoglobulins of a monotreme mammal, the echidna Tachyglossus aculeatus, bind to Staphylococcus aureus A protein coupled to an insoluble matrix. This binding supports the homology between the previously described echidna IgG and IgG molecules of higher mammals and provides a rapid, simple method for the isolation of this protein from echidna serum. In addition, another echidna 7S immunoglobulin became bound to protein A-Sepharose. The major protein A-binding immunoglobulin has a slow electrophoretic mobility and possesses a heavy chain comparable in mass to typical mammalian γ chains (52,000 daltons). We suggest the designation IgG2 for this immunoglobulin. The minor protein A-binding immunoglobulin is electrophoretically faster than IgG2 and can be resolved from the former by gradient elution from DEAE-Biogel. We propose the nomenclature IgG1 for this molecule although we cannot discount the possibility that it might represent another main class such as IgA. The γ1 heavy chain is distinguishable from the γ2 chain on polyacrylamide gel electrophoresis in sodium dodecylsulphate containing buffers. The γ1 chain possesses a nominal mass of 61,000 daltons. The intact molecule has an apparent mass of 177,000 Daltons and comprises two pairs of light and heavy chains.

Calcium-binding and structural stability of echidna and canine milk lysozymes.

Kikuchi, M.; Kawano, K.; Nitta, K.
Fonte: Cold Spring Harbor Laboratory Press Publicador: Cold Spring Harbor Laboratory Press
Tipo: Artigo de Revista Científica
Publicado em /10/1998 EN
Relevância na Pesquisa
28%
For echidna and canine milk lysozymes, which were presumed to be the calcium-binding lysozymes by their amino acid sequences, we have quantitated their calcium-binding strength and examined their guanidine unfolding profiles. The calcium-binding constants of echidna and canine lysozymes were determined to be 8.6 x 10(6) M(-1) and 8.9 x 10(6) M(-1) in 0.1 M KCl at pH 7.1 and 20 C, respectively. The unfolding of decalcified canine lysozyme proceeds in the same manner as that of alpha-lactalbumin, through a stable molten globule intermediate. However, neither calcium-bound nor decalcified echidna lysozyme shows a stable molten globule intermediate. This unfolding profile of echidna lysozyme is identical to that of conventional lysozymes and pigeon egg-white lysozyme, avian calcium-binding lysozyme. This result supports the suggestion of Prager and Jolles (Prager EM, Jolles P. 1996. Animal lysozymes c and g: An overview. In: Jolles P, ed. Lysozymes: Model enzymes in biochemistry and biology. Basel-Boston-Berlin: Birkhauzer Verlag. pp 9-31) that the lineage of avian and echidna calcium-binding lysozymes and that of eutherian calcium-binding lysozymes diverged separately from that of conventional lysozymes.

Assessment of the hemorheological profile of koala and echidna

Baskurt, Oguz K.; Marshall-Gradisnik, Sonya; Pyne, Michael; Simmonds, Michael; Brenu, Ekua; Christy, Rhys; Meiselman, Herbert J.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /03/2010 EN
Relevância na Pesquisa
28.13%
Koala, a marsupial, and echidna, a monotreme, are mammals native to Australia. Blood viscosity (62.5–1250 s−1), red blood cell (RBC) deformability, RBC aggregation, aggregability and surface charge, and hematological parameters were measured in blood samples from six koalas and six echidnas and compared to adult human blood. Koala had the largest RBC mean cell volume (107.7 ± 2.6 fl) compared to echidna (81.3 ± 2.6 fl) and humans (88.4 ± 1.2 fl). Echidna blood exhibited the highest viscosity over the entire range of shear rates. Echidna RBC were significantly less deformable than koala RBC but more deformable than human RBC. Echidna RBC had significantly lower aggregability (i.e., aggregation in standardized dextran medium) than koala or human RBC, while aggregation in autologous plasma was similar for the three species. Erythrocyte surface charge as indexed by RBC electrophoretic mobility was similar for human and echidna cells but was 40 % lower for koala RBC. Data obtained during this preliminary study indicate that koala and echidna have distinct hemorheological characteristics; investigation of these properties may reveal patterns relevant to specific behavioral and physiological features of these animals.

Distortion Product Otoacoustic Emission and Auditory Brainstem Responses in the Echidna (Tachyglossus aculeatus)

Mills, David M.; Shepherd, Robert K.
Fonte: Springer-Verlag Publicador: Springer-Verlag
Tipo: Artigo de Revista Científica
Publicado em /06/2001 EN
Relevância na Pesquisa
27.9%
The auditory function of four wild-caught echidnas was measured using distortion product otoacoustic emissions (DPOAEs) and auditory brainstem responses (ABRs). Emission audiograms were constructed by finding the stimulus levels required to produce a criterion emission amplitude at a given stimulus frequency. For an emission amplitude of -10 dB SPL, the median "best threshold" was 28 dB SPL, and this minimum threshold occurred between 4 and 8 kHz for all animals. The relative effective range of auditory function was defined by the frequencies at which the audiogram was 30 dB above its best threshold. For the emission audiograms, the median lower-frequency limit was 2.3 kHz, the upper limit was 18.4 kHz, and the effective range was 2.7 octaves. The audiogram as measured by ABR was also found to be strongly "U" shaped with similar low- and high-frequency limits, i.e., from 1.6 to 13.9 kHz, with an effective range of 3.1 octaves. These results suggest that the echidna has a behavioral hearing sensitivity comparable to that of typical therian mammals (e.g., rabbits and gerbils) but with a significantly narrower frequency range. DPOAE responses were also measured in selected animals as a function of the variation of all four stimulus parameters (frequencies and intensities of both stimulus tones). Overall...

Twentieth century occurrence of the Long-Beaked Echidna Zaglossus bruijnii in the Kimberley region of Australia

Helgen, Kristofer M.; Miguez, Roberto Portela; James L. Kohen, ;  Lauren E. Helgen,
Fonte: Pensoft Publishers Publicador: Pensoft Publishers
Tipo: Artigo de Revista Científica
Publicado em 28/12/2012 EN
Relevância na Pesquisa
27.57%
The monotreme genus Zaglossus, the largest egg-laying mammal, comprises several endangered taxa today known only from New Guinea. Zaglossus is considered to be extinct in Australia, where its apparent occurrence (in addition to the large echidna genus Megalibgwilia) is recorded by Pleistocene fossil remains, as well as from convincing representations in Aboriginal rock art from Arnhem Land (Northern Territory). Here we report on the existence and history of a well documented but previously overlooked museum specimen (skin and skull) of the Western Long-Beaked Echidna (Zaglossus bruijnii) collected by John T. Tunney at Mount Anderson in the West Kimberley region of northern Western Australia in 1901, now deposited in the Natural History Museum, London. Possible accounts from living memory of Zaglossus are provided by Aboriginal inhabitants from Kununurra in the East Kimberley. We conclude that, like Tachyglossus, Zaglossus is part of the modern fauna of the Kimberley region of Western Australia, where it apparently survived as a rare element into the twentieth century, and may still survive.

Echidna Venom Gland Transcriptome Provides Insights into the Evolution of Monotreme Venom

Wong, Emily S. W.; Nicol, Stewart; Warren, Wesley C.; Belov, Katherine
Fonte: Public Library of Science Publicador: Public Library of Science
Tipo: Artigo de Revista Científica
Publicado em 12/11/2013 EN
Relevância na Pesquisa
28.24%
Monotremes (echidna and platypus) are egg-laying mammals. One of their most unique characteristic is that males have venom/crural glands that are seasonally active. Male platypuses produce venom during the breeding season, delivered via spurs, to aid in competition against other males. Echidnas are not able to erect their spurs, but a milky secretion is produced by the gland during the breeding season. The function and molecular composition of echidna venom is as yet unknown. Hence, we compared the deeply sequenced transcriptome of an in-season echidna crural gland to that of a platypus and searched for putative venom genes to provide clues into the function of echidna venom and the evolutionary history of monotreme venom. We found that the echidna venom gland transcriptome was markedly different from the platypus with no correlation between the top 50 most highly expressed genes. Four peptides found in the venom of the platypus were detected in the echidna transcriptome. However, these genes were not highly expressed in echidna, suggesting that they are the remnants of the evolutionary history of the ancestral venom gland. Gene ontology terms associated with the top 100 most highly expressed genes in echidna, showed functional terms associated with steroidal and fatty acid production...

Sex determination in platypus and echidna: autosomal location of SOX3 confirms the absence of SRY from monotremes

Wallis, M.; Waters, P.; Delbridge, M.; Kirby, P.; Pask, A.; Grutzner, F.; Rens, W.; Ferguson-Smith, M.; Graves, J.
Fonte: Kluwer Academic Publ Publicador: Kluwer Academic Publ
Tipo: Artigo de Revista Científica
Publicado em //2007 EN
Relevância na Pesquisa
27.9%
In eutherian (‘placental’) mammals, sex is determined by the presence or absence of the Y chromosome-borne gene SRY, which triggers testis determination. Marsupials also have a Y-borne SRY gene, implying that this mechanism is ancestral to therians, the SRY gene having diverged from its X-borne homologue SOX3 at least 180 million years ago. The rare exceptions have clearly lost and replaced the SRY mechanism recently. Other vertebrate classes have a variety of sex-determining mechanisms, but none shares the therian SRY-driven XX female:XY male system. In monotreme mammals (platypus and echidna), which branched from the therian lineage 210 million years ago, no orthologue of SRY has been found. In this study we show that its partner SOX3 is autosomal in platypus and echidna, mapping among human X chromosome orthologues to platypus chromosome 6, and to the homologous chromosome 16 in echidna. The autosomal localization of SOX3 in monotreme mammals, as well as non-mammal vertebrates, implies that SRY is absent in Prototheria and evolved later in the therian lineage 210–180 million years ago. Sex determination in platypus and echidna must therefore depend on another male-determining gene(s) on the Y chromosomes, or on the different dosage of a gene(s) on the X chromosomes.; M. C. Wallis...

Disruption and pseudoautosomal localization of the major histocompatibility complex in monotremes

Dohm, J.; Tsend-Ayush, E.; Reinhardt, R.; Grutzner, F.; Himmelbauer, H.
Fonte: BioMed Central Publicador: BioMed Central
Tipo: Artigo de Revista Científica
Publicado em //2007 EN
Relevância na Pesquisa
27.9%
Background: The monotremes, represented by the duck-billed platypus and the echidnas, are the most divergent species within mammals, featuring a flamboyant mix of reptilian, mammalian and specialized characteristics. To understand the evolution of the mammalian major histocompatibility complex (MHC), the analysis of the monotreme genome is vital. Results: We characterized several MHC containing bacterial artificial chromosome clones from platypus (Ornithorhynchus anatinus) and the short-beaked echidna (Tachyglossus aculeatus) and mapped them onto chromosomes. We discovered that the MHC of monotremes is not contiguous and locates within pseudoautosomal regions of two pairs of their sex chromosomes. The analysis revealed an MHC core region with class I and class II genes on platypus and echidna X3/Y3. Echidna X4/Y4 and platypus Y4/X5 showed synteny to the human distal class III region and beyond. We discovered an intron-containing class I pseudogene on platypus Y4/X5 at a genomic location equivalent to the human HLA-B,C region, suggesting ancestral synteny of the monotreme MHC. Analysis of male meioses from platypus and echidna showed that MHC chromosomes occupy different positions in the meiotic chains of either species. Conclusion: Molecular and cytogenetic analyses reveal new insights into the evolution of the mammalian MHC and the multiple sex chromosome system of monotremes. In addition...

Reproductive biology in egg-laying mammals

Grutzner, F.; Nixon, B.; Jones, R.
Fonte: S. Karger AG Publicador: S. Karger AG
Tipo: Artigo de Revista Científica
Publicado em //2008 EN
Relevância na Pesquisa
27.57%
The duck-billed platypus and short-beaked echidna are iconic species in Australia. Their morphology and physiology have puzzled scientists all over the world for more than 200 years. Recent genetic studies, particularly the platypus whole-genome sequencing project, have revealed the molecular basis of some of the extraordinary characteristics of monotremes. This and other works demonstrate the great value of research on our most distantly related mammalian relatives for comparative genomics and developmental biology. In this review we focus on the reproductive biology of monotremes and discuss works that unravel genes involved in lactation, testicular descent, gamete biology and fertilization, and early development. In addition we discuss works on the evolution of the complex sex chromosome system in platypus and echidna, which has also significant impact on our general understanding of mammalian sex chromosomes and sex determination.; F. Grützner, B. Nixon, R.C. Jones

Immunohistochemical analysis of pancreatic islets of platypus (Ornithorhynchus anatinus) and echidna (Tachyglossus aculeatus ssp.)

He, C.; Myers, M.A.; Forbes, B.E.; Grützner, F.
Fonte: Wiley Publicador: Wiley
Tipo: Artigo de Revista Científica
Publicado em //2015 EN
Relevância na Pesquisa
37.9%
Monotremes have undergone remarkable changes to their digestive and metabolic control system; however, the monotreme pancreas remains poorly characterized. Previous work in echidna demonstrated the presence of pancreatic islets, but no information is available for platypus and the fine structure has not been described for either monotreme. Based on our recent finding that monotremes lack the ghrelin gene, which is expressed in mouse and human pancreatic islets, we investigated the structure of monotreme islets in more detail. Generally, as in birds, the islets of monotremes were smaller but greater in number compared with mouse. β-cells were the most abundant endocrine cell population in platypus islets and were located peripherally, while α-cells were observed both in the interior and periphery of the islets. δ-cells and pancreatic polypeptide (PP)-cells were mainly found in the islet periphery. Distinct PP-rich (PP-lobe) and PP-poor areas (non-PP-lobe) are present in therian mammals, and we identified these areas in echidna but not platypus pancreas. Interestingly, in some of the echidna islets, α- and β-cells tended to form two poles within the islets, which to our knowledge is the first time this has been observed in any species. Overall...

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

Rens, W.; O'Brien, P.; Grutzner, F.; Clarke, O.; Graphodatskaya, D.; Tsend-Ayush, E.; Trifonov, V.; Skelton, H.; Wallis, M.; Johnston, S.; Veyrunes, F.; Graves, J.; Ferguson-Smith, M.
Fonte: BioMed Central Ltd. Publicador: BioMed Central Ltd.
Tipo: Artigo de Revista Científica
Publicado em //2007 EN
Relevância na Pesquisa
27.9%
Background: Sex-determining systems have evolved independently in vertebrates. Placental mammals and marsupials have an XY system, birds have a ZW system. Reptiles and amphibians have different systems, including temperature-dependent sex determination, and XY and ZW systems that differ in origin from birds and placental mammals. Monotremes diverged early in mammalian evolution, just after the mammalian clade diverged from the sauropsid clade. Our previous studies showed that male platypus has five X and five Y chromosomes, no SRY, and DMRT1 on an X chromosome. In order to investigate monotreme sex chromosome evolution, we performed a comparative study of platypus and echidna by chromosome painting and comparative gene mapping. Results: Chromosome painting reveals a meiotic chain of nine sex chromosomes in the male echidna and establishes their order in the chain. Two of those differ from those in the platypus, three of the platypus sex chromosomes differ from those of the echidna and the order of several chromosomes is rearranged. Comparative gene mapping shows that, in addition to bird autosome regions, regions of bird Z chromosomes are homologous to regions in four platypus X chromosomes, that is, X1, X2, X3, X5, and in chromosome Y1. Conclusion: Monotreme sex chromosomes are easiest to explain on the hypothesis that autosomes were added sequentially to the translocation chain...

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; Grutzner, 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
Relevância na Pesquisa
38%
BACKGROUND Sex-determining systems have evolved independently in vertebrates. Placental mammals and marsupials have an XY system, birds have a ZW system. Reptiles and amphibians have different systems, including temperature-dependent sex determination, and XY and ZW systems that differ in origin from birds and placental mammals. Monotremes diverged early in mammalian evolution, just after the mammalian clade diverged from the sauropsid clade. Our previous studies showed that male platypus has five X and five Y chromosomes, no SRY, and DMRT1 on an X chromosome. In order to investigate monotreme sex chromosome evolution, we performed a comparative study of platypus and echidna by chromosome painting and comparative gene mapping. RESULTS Chromosome painting reveals a meiotic chain of nine sex chromosomes in the male echidna and establishes their order in the chain. Two of those differ from those in the platypus, three of the platypus sex chromosomes differ from those of the echidna and the order of several chromosomes is rearranged. Comparative gene mapping shows that, in addition to bird autosome regions, regions of bird Z chromosomes are homologous to regions in four platypus X chromosomes, that is, X1, X2, X3, X5, and in chromosome Y1. CONCLUSION Monotreme sex chromosomes are easiest to explain on the hypothesis that autosomes were added sequentially to the translocation chain...

Phylogenetic studies on the immune response: III. Autoradiographic studies on the lymphoid system of the Australian echidna Tachyglossus aculeatus*

Diener, E.; Ealey, E. H. M.; Legge, J. S.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /10/1967 EN
Relevância na Pesquisa
27.57%
In the Australian echidna Tachyglossus aculeatus, a close relative of the extinct ancestors of higher mammals, the lymphoid organs were investigated by means of autoradiographic studies after the injection of [3H]thymidine and 125I-labelled flagellar antigen of Salmonella adelaide. The histology of organs from echidnas injected with colloidal carbon was studied in parallel. The results lead to the conclusion that each lymph nodule in the echidna represents a single lymphoid follicle comparable to a cortical follicle in lymph nodes of higher mammals. Studies on lymph nodules of echidnas injected with [3H]thymidine revealed the presence of highly active germinal centres, usually one per nodule. Antigen became localized first around the entire nodule; later on it was found within the germinal centre or in its peripheral parts. Often a germinal centre was eccentrically located, in which case the labelled antigen formed the typical germinal centre cap known to be characteristic of secondary follicles in the rat lymph node. A significant uptake of antigen was also seen in the appendix, the Peyer's patches of the gut and in the Hassall's corpuscles of the thymus.

Core-SINE blocks comprise a large fraction of monotreme genomes; implications for vertebrate chromosome evolution

Kirby, Patrick J; Greaves, Ian; Koina, Edda; Waters, Paul; Graves, Jennifer
Fonte: Kluwer Academic Publishers Publicador: Kluwer Academic Publishers
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
27.57%
The genomes of the egg-laying platypus and echidna are of particular interest because monotremes are the most basal mammal group. The chromosomal distribution of an ancient family of short interspersed repeats (SINEs), the core-SINEs, was investigated to

(42355) Typhon-Echidna: Scheduling Observations for Binary Orbit Determination

Grundy, W. M.; Noll, K. S.; Virtanen, J.; Muinonen, K.; Kern, S. D.; Stephens, D. C.; Stansberry, J. A.; Levison, H. F.; Spencer, J. R.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 15/04/2008
Relevância na Pesquisa
27.76%
We describe a strategy for scheduling astrometric observations to minimize the number required to determine the mutual orbits of binary transneptunian systems. The method is illustrated by application to Hubble Space Telescope observations of (42355) Typhon-Echidna, revealing that Typhon and Echidna orbit one another with a period of 18.971 +/- 0.006 days and a semimajor axis of 1628 +/- 29 km, implying a system mass of (9.49 +/- 0.52) x 10^17 kg. The eccentricity of the orbit is 0.526 +/- 0.015. Combined with a radiometric size determined from Spitzer Space Telescope data and the assumption that Typhon and Echidna both have the same albedo, we estimate that their radii are 76 +14/-16 and 42 +8/-9 km, respectively. These numbers give an average bulk density of only 0.44 +0.44/-0.17 g cm^-3, consistent with very low bulk densities recently reported for two other small transneptunian binaries.

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 C. M.; Grutzner, Frank; Clarke, Oliver; Graphodatskaya, Daria; Tsend-Ayush, Enkhjargal; Trifonov, Vladimir A.; Skelton, Helen; Wallis, Mary C.; Johnston, Steve; Veyrunes, Frederic; Graves, Jennifer A. M.; Ferguson-Smith, Ma
Fonte: Universidade de Cambridge Publicador: Universidade de Cambridge
Tipo: Article; Published Version
EN
Relevância na Pesquisa
27.9%
RIGHTS : This article is licensed under the BioMed Central licence at http://www.biomedcentral.com/about/license which is similar to the 'Creative Commons Attribution Licence'. In brief you may : copy, distribute, and display the work; make derivative works; or make commercial use of the work - under the following conditions: the original author must be given credit; for any reuse or distribution, it must be made clear to others what the license terms of this work are.; Abstract Background Sex-determining systems have evolved independently in vertebrates. Placental mammals and marsupials have an XY system, birds have a ZW system. Reptiles and amphibians have different systems, including temperature-dependent sex determination, and XY and ZW systems that differ in origin from birds and placental mammals. Monotremes diverged early in mammalian evolution, just after the mammalian clade diverged from the sauropsid clade. Our previous studies showed that male platypus has five X and five Y chromosomes, no SRY, and DMRT1 on an X chromosome. In order to investigate monotreme sex chromosome evolution, we performed a comparative study of platypus and echidna by chromosome painting and comparative gene mapping. Results Chromosome painting reveals a meiotic chain of nine sex chromosomes in the male echidna and establishes their order in the chain. Two of those differ from those in the platypus...

Evolution of mammalian sex chromosomes and sex determination genes: insights from monotremes.

Toledo-Flores, Deborah Fernanda
Fonte: Universidade de Adelaide Publicador: Universidade de Adelaide
Tipo: Tese de Doutorado
Publicado em //2015
Relevância na Pesquisa
27.76%
Genetic sex determination systems are generally based on the presence of differentiated sex chromosomes. Birds have a ZZ/ZW sex chromosome system in which males are ZZ and females ZW, whereas mammals have an XX/XY system with males being XY and females XX. Monotremes have an extraordinary sex chromosome system that consists of multiple sex chromosomes: 5X5Y in platypus and 5X4Y in echidna. Intriguingly, the monotreme sex chromosomes show extensive homology to the bird ZW and not to the therian XY. However, sex determination in monotremes is still a mystery; the Y-specific Sry gene that triggers male sex determination in therian mammals is absent and so far very few genes have been identified on Y chromosomes in monotremes. To gain more insights into the gene content of Y-chromosomes and to identify potential sex determination genes in the platypus a collaborative large scale transcriptomic approach led to the identification of new male specific genes including the anti-Muellerian hormone AMH that I mapped to Y₅, this makes Amhy an exciting new candidate for sex determination in monotremes. Platypus chromosome 6 is largely homologous to the therian X and therefore it represents the therian proto sex chromosome. In addition, this autosome features a large heteromorphic nucleolus organizer region (NOR) and associates with the sex chromosomes during male meiosis (Casey and Daish personal communication). I investigated chromosome 6 heteromorphism in both sexes and found a number of sex-specific characteristics related to the extent of the NOR heteromorphism...