Low-Frequency Shear Parameters Viscoelastic Relaxation Process

An experimental study of the shear parameters of viscoelastic liquids is carried out by the acoustic resonance method based on the changes in the natural frequency and Q factor of a piezoelectric quartz resonator. The liquid to be studied is placed between a stationary quartz strap and the piezoelectric quartz crystal vibrating at the resonance frequency. For a set of drilling mud, the values of the real and imaginary shear module are obtained at a frequency of 74 kHz. The measurements are performed with a liquid layer thickness much smaller than the shear wavelength. It is shown that the shear modulus decreases with increasing strain amplitude. A hole-cluster model based on the Isakovich- Chaban nonlocal diffusion theory is proposed for explaining the low-frequency viscoelastic relaxation process.DOI: http://dx.doi.org/10.5564/pmas.v0i4.46 Proceedings of the Mongolian Academy of Sciences 2009 No 4 pp.53-5

Monotreme glucagon-like peptide-1 in venom and gut: one gene – two very different functions

This work is licensed under a Creative Commons Attribution 4.0 International License. The images or other third party material in this article are included in the article’s Creative Commons license, unless indicated otherwise in the credit line; if the material is not included under the Creative Commons license, users will need to obtain permission from the license holder to reproduce the material. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/The importance of Glucagon like peptide 1 (GLP-1) for metabolic control and insulin release sparked the evolution of genes mimicking GLP-1 action in venomous species (e.g. Exendin-4 in Heloderma suspectum (gila monster)). We discovered that platypus and echidna express a single GLP-1 peptide in both intestine and venom. Specific changes in GLP-1 of monotreme mammals result in resistance to DPP-4 cleavage which is also observed in the GLP-1 like Exendin-4 expressed in Heloderma venom. Remarkably we discovered that monotremes evolved an alternative mechanism to degrade GLP-1. We also show that monotreme GLP-1 stimulates insulin release in cultured rodent islets, but surprisingly shows low receptor affinity and bias toward Erk signaling. We propose that these changes in monotreme GLP-1 are the result of conflicting function of this peptide in metabolic control and venom. This evolutionary path is fundamentally different from the generally accepted idea that conflicting functions in a single gene favour duplication and diversification, as is the case for Exendin-4 in gila monster. This provides novel insight into the remarkably different metabolic control mechanism and venom function in monotremes and an unique example of how different selective pressures act upon a single gene in the absence of gene duplication

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

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, female platypuses express higher levels of telomerase in heart and liver tissues than do males. Conclusions OanTERT shares many features with TERT of the reptilian outgroup, suggesting that OanTERT represents the ancestral mammalian TERT. Features specific to TERT of eutherian mammals have, therefore, evolved more recently after the divergence of monotremes.Radmila Hrdličková, Jiří Nehyba, Shu Ly Lim, Frank Grützner, Henry R Bose J

Platypus have four male-specific chromosomes that segregate together at meiosis

More than 200 years after the discovery of the platypus, monotreme chromosomes remain deeply puzzling. Karyotypes of both sexes were claimed to contain a set of chromosomes for which no homologues could be identified. At male meiosis these presumably translocated chromosomes assemble in a multivalent chain involving the X chromosome. Such a system of translocation heterozygosity is unprecedented in vertebrates, although similar systems are found naturally in some plants and a few social insects. Mice heterozygous for autosomal translocations can be deliberately bred, but have severe meiotic defects and produce high proportions of aneuploid sperm. The number, identity and homology relationships of the translocated chromosomes have been controversial over the past 30 years, as has their role in sex determination and their segregation to form balanced gametes. In order to solve the complex chromosome system in platypus we have generated chromosome paints for 20 platypus chromosomes and hybridised these paints on male and female metaphase chromosomes as well as meiotic cells and sperm. Five paints show a different hybridisation pattern on male and female chromosomes. Four chromosomes (including the X) were identified that are present in one copy in males and in two copies in females. Additionally, four male-specific chromosomes have been identified that detect no homologues in females, but share sequences with other unpaired chromosomes. One of these has complete homology to the short arm of the X. BAC clones from one of the male specific chromosomes contain male-specific sequences. Position of these chromosomes at different meiotic stages revealed a consistent order of chromosomes within the meiotic chain. Co-localisation of these elements on mature sperm provides the first direct evidence that two different sperm types are produced as a result of alternate segregation in platypus.Frank Grützner, Willem Rens, Russell Jones, Enkhjargal Tsend-Ayush, Jennifer A. Marshall Graveshttp://hgm2004.hgu.mrc.ac.uk/Abstracts/Publish/WorkshopPosters/WorkshopPosters12/hgm308.htm

Assignment1 of the DMRT1 gene to tammar wallaby chromosome 3p by fluorescence in situ hybridization

N. El-Mogharbel, J. Deakin, E. Tsend-Ayush, A. Pask and J.A.M. Grave

Conservation and expression of piRNA pathway genes in male and female adult gonad of amniotes

The PIWI-interacting RNA (piRNA) pathway is essential for germline development and transposable element repression. Key elements of this pathway are members of the piRNA-binding PIWI/Argonaute protein family and associated factors (e.g., VASA, MAELSTROM, and TUDOR domain proteins). PIWI-interacting RNAs have been identified in mouse testis and oocytes, but information about the expression of the different piRNA pathway genes, in particular in the mammalian ovary, remains incomplete. We investigated the evolution and expression of piRNA pathway genes in gonads of amniote species (chicken, platypus, and mouse). Database searches confirm a high level of conservation and revealed lineage-specific gain and loss of Piwi genes in vertebrates. Expression analysis in mammals shows that orthologs of Piwi-like (Piwil) genes, Mael (Maelstrom), Mvh (mouse vasa homolog), and Tdrd1 (Tudor domain-containing protein 1) are expressed in platypus adult testis. In contrast to mouse, Piwil4 is expressed in platypus and human adult testis. We found evidence for Mael and Piwil2 expression in mouse Sertoli cells. Importantly, we show mRNA expression of Piwil2, Piwil4, and Mael in oocytes and supporting cells of human, mouse, and platypus ovary. We found no Piwil1 expression in mouse and chicken ovary. The conservation of gene expression in somatic parts of the gonad and germ cells of species that diverged over 800 million yr ago indicates an important role in adult male and female gonad.Shu Ly Lim, Enkhjargal Tsend-Ayush, R. Daniel Kortschak, Reuben Jacob, Carmela Ricciardelli, Martin K. Oehler, and Frank Grützne

Plasticity of human chromosome 3 during primate evolution

Comparative FISH mapping of some 150 YAC and BAC clones from human chromosome 3 in orangutans (PPY), siamang gibbon (HSY), silvered-leaf monkey (PCR) and Geoffroys marmoset (CGE) revealed that hominoid chromosome evolution is more complex than suggested by classical chromosome banding and painting. The large-scale inversions, fissions and translocations in the five primate species studied involve at least 14 different evolutionary breakpoints. Many evolutionary rearrangements, i.e. the pericentric inversions leading to PPY 2, were not simple breakage and reunion events. The breakpoint regions that distinguish HSA 3p25.1, 3p12.3 and 3q21 from PPY 2 contain paralogous sequence blocks, which were prone to microduplications and microdeletions during evolution of the hominoid genome. A 6.5 Mb interval syntenic to HSA 3q21 contains four independent evolutionary breakpoints, namely at 130-132 Mb in PPY, 130-133.8 Mb in HSY, 127.3-132 Mb in PCR and 130-132 Mb in CGE. By FISH, three breakpoints in orangutan, gibbon and Old World monkey were localized in a 320 kb contig of BACs RP11-93K22, RP11-77P16 and RP11-687B8. 35 PCR primer pairs which amplify specific DNA fragments along the entire length of this contig were tested on flow sorted PPY and HSY chromosomes and the respective breakpoints were narrowed further to a 230 kb interval in RP11-93K22 and RP11-77P16. About 200 kb of this contig were deleted from the HSA 3q21-syntenic inversion breakpoint in PPY 2 and the translocation breakpoint leading to HSY 10 and 21. The deleted segment represents part of an ancestral duplication of HSA 3q21-paralogous sequences in human, orangutan and gibbon genomes. Collectively, our results suggest that particular regions in the hominoid genome are more susceptible to evolutionary chromosome reshuffling. Large-scale chromosome rearrangements, microduplications and microdeletions can be considered as different aspects of an inherent instability of these regions. Genome architecture involving low-copy repeats has played an important role during primate speciation.Ying Yue, Bärbel Grossmann, Enkhjargal Tsend-Ayush, Frank Grützner, Malcolm Ferguson-Smith, Fengtang Yang, Thomas Haa

Chicken microchromosomes are hypermethylated and can be identified by specific painting probes

Copyright © 2001 S. Karger AGMicrodissection of single chicken microchromosomes (MICs) followed by degenerate oligonucleotide-primed (DOP) PCR allows the rapid generation of MIC-specific DNA libraries. Since some libraries derived from a single (or a few) chromosome(s) label the entire MIC fraction, the majority of chicken MICs share repetitive DNA sequences that are not found on the macrochromosomes. In evolutionarily distant bird species, MICs are invariably hypermethylated. Methylcytosine staining provides additional in situ evidence for the high gene content of MICs and strong compartmentalization of avian genomes.F. Grützner, E. Zend-Ajusch, K. Stout, S. Munsche, A. Niveleau, I. Nanda, M. Schmid and T. Haa