Endogenous retroviral elements in the canine genome

Defective endogenous retroviral elements have recently been found in a canine lymphosarcoma (LSA) cell line and we have characterized these by DNA sequencing. This study was designed to determine if similar elements are present in naturally-occurring canine LSAs or in normal canine DNA. Two probes were prepared by sub-cloning sequences from the 5' and 3' ends of the canine endogenous retroviralpol gene. Probes were chosen from areas sharing at least 60% homology and complete colinearity with AKV murine leukemia virus. High molecular weight genomic DNA was prepared from a variety of canine tissues: 12 samples were from LSA lymph nodes, 2 from lymphoblasts in cases of acute lymphoblastic leukemia and 7 from normal kidney. Genomic DNA was digested with restriction endonucleases and fragments were separated by agarose gel electrophoresis. Southern transfer and hybridization under stringent conditions with the canine retroviral probes revealed numerous retroviral bands. The pattern of bands was identical for all tissues examined. Similar treatment of DNA from the original LSA cell Line from which the probes were derived produced an identical pattern of bands. In summary, canine DNA has been shown to contain multiple copies of endogenous retroviral elements. No difference in the pattern of proviral bands has been observed between normal and LSA tissues, so no etiological significance can yet be ascribed to these elements. Further studies are in progress to determine whether any of these elements erpress themselves at the RNA or protein level

Defective endogenous retroviral elements in a canine lyphosarcoma cell line

A canine lymphosarcoma (LSA) cell has has been reported to produce particles with properties characteristic of mammalian retroviruses. However, it has proved difficult to reproduce this result. To search for retroviral proviral elements in this cell h e a bacteriophage Lambda genomic DNA library was made. The library was probed with a murine retrovirus (FMuLV) and hybridizing phage plaques were picked. DNA extracted from hybridizing phages was digested with restriction endonucleases and fragments were separated by agarose gel electrophoresis. Southern transfer and hybridization with FMuLV and baboon endogenous retrovirus (BaEV) revealed that 2 phage clones contained fragments which hybridized strongly with both FMuLV and BaEV. These fragments were subcloned into the plasmid vector "Bluescript" and sequenced by the dideoxy chain termination method.\ud \ud DNA sequence analysis identified 2 distinct elements homologous with a variety of retroviruses.The larger fragment (2.5 kilobase pairs) contained 1.5kbp of a defective retroviral pol gene sharing 63% homology at the DNA level with AKV murine leukemia virus. The smaller fragment (0.45kb) consisted exclusively of retroviral pol gene almost identical to that in the large fragment, but with an additional 4Obp deletion. Sequencing on either side of these fragments is continuing.\ud \ud In summary, defective endogenous retroviral elements have been found in a canine LSA cell he. The elements differ in their defects but appear otherwise to be closely related. Because of their defects, these elements could not be responsible for the production of intact retroviruses as reported in this cell line. Further study is in progress to determine whether other endogenous elements capable of producing intact retroviruses are present in this cell line. It is of interest to determine the prevalence of retroviral elements in normal canine DNA and to investigate whether they are of etiological significance in canine diseases

nIFTy cosmology: comparison of galaxy formation models

We present a comparison of 14 galaxy formation models: 12 different semi-analytical models and 2 halo occupation distribution models for galaxy formation based upon the same cosmological simulation and merger tree information derived from it. The participating codes have proven to be very successful in their own right but they have all been calibrated independently using various observational data sets, stellar models, and merger trees. In this paper, we apply them without recalibration and this leads to a wide variety of predictions for the stellar mass function, specific star formation rates, stellar-to-halo mass ratios, and the abundance of orphan galaxies. The scatter is much larger than seen in previous comparison studies primarily because the codes have been used outside of their native environment within which they are well tested and calibrated. The purpose of the ‘nIFTy comparison of galaxy formation models’ is to bring together as many different galaxy formation modellers as possible and to investigate a common approach to model calibration. This paper provides a unified description for all participating models and presents the initial, uncalibrated comparison as a baseline for our future studies where we will develop a common calibration framework and address the extent to which that reduces the scatter in the model predictions seen here