Molecular breeding of viruses

Genetic recombination is a major force driving the evolution of many viruses. Recombination between two copackaged retroviral genomes may occur at rates as high as 40% per replication cycle. This enables genetic information to be shuffled rapidly, leading to recombinants with new patterns of mutations and phenotypes. The in vitro process of DNA shuffling (molecular breeding) mimics this mechanism on a vastly parallel and accelerated scale. Multiple homologous parental sequences are recombined in parallel, leading to a diverse library of complex recombinants from which desired improvements can be selected. Different proteins and enzymes have been improved using DNA shuffling. We report here the first application of molecular breeding to viruses. A single round of shuffling envelope sequences from six murine leukaemia viruses (MLV) followed by selection yielded a chimaeric clone with a completely new tropism for Chinese Hamster Ovary (CHOK1) cells. The composition and properties of the selected clone indicated that this particular permutation of parental sequences cannot be readily attained by natural retroviral recombination. This example demonstrates that molecular breeding can enhance the inherently high evolutionary potential of retroviruses to obtain desired phenotypes. It can be an effective tool, when information is limited, to optimize viruses for gene therapy and vaccine applications when multiple complex functions must be simultaneously balanced.     

Loss of integrin alpha(v)beta8 on dendritic cells causes autoimmunity and colitis in mice

The cytokine transforming growth factor-beta (TGF-beta) is an important negative regulator of adaptive immunity. TGF-beta is secreted by cells as an inactive precursor that must be activated to exert biological effects, but the mechanisms that regulate TGF-beta activation and function in the immune system are poorly understood. Here we show that conditional loss of the TGF-beta-activating integrin alpha(v)beta8 on leukocytes causes severe inflammatory bowel disease and age-related autoimmunity in mice. This autoimmune phenotype is largely due to lack of alpha(v)beta8 on dendritic cells, as mice lacking alpha(v)beta8 principally on dendritic cells develop identical immunological abnormalities as mice lacking alpha(v)beta8 on all leukocytes, whereas mice lacking alpha(v)beta8 on T cells alone are phenotypically normal. We further show that dendritic cells lacking alpha(v)beta8 fail to induce regulatory T cells (T(R) cells) in vitro, an effect that depends on TGF-beta activity. Furthermore, mice lacking alpha(v)beta8 on dendritic cells have reduced proportions of T(R) cells in colonic tissue. These results suggest that alpha(v)beta8-mediated TGF-beta activation by dendritic cells is essential for preventing immune dysfunction that results in inflammatory bowel disease and autoimmunity, effects that are due, at least in part, to the ability of alpha(v)beta8 on dendritic cells to induce and/or maintain tissue T(R) cells.     

Immunochemical differentiation between gastrin and related peptide hormones through a novel conjugation of peptides to proteins

Zusammenfassung Nachweis, dass mit Hilfe von 2,4-Dichlor-6-methoxy-1,3,5-triazin Tyrosinreste von Peptiden und Lysinreste von Proteinen miteinander verknüpft werden können. Auf dieser Basis wurde ein immunologischer Test für die Sequenz 1–13 von menschlichem Gastrin entwickelt.     

Lateral heterogeneity in the Earth's mantle

The characteristics of seismic waves detected at the Large Aperture Seismic Array in Montana suggest that, beneath the Bonin Island Arc in particular, there are lateral inhomogeneities in the mantle.     

A synthetic cyclol tripeptide

Zusammenfassung Das dem-Methylalanyl--methylalanyl--methylalanin entsprechende Oxazolon (III) isomerisiert leicht zum kristallisierten Cyclol (IV), dessen Struktur sich aus dem Übergang in das Imidazolon (V) unter Wasserabspaltung ergibt.