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Archive - May 14, 2017

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Japanese Scientists Isolate Gene Critical for Plant Health; Study Shows That Holliday Junction Resolvases Mediate Chloroplast Nucleoid Segregation

Proper DNA inheritance is essential for healthy cell growth and division. The same goes for the genetic material found in chloroplasts: the energy centers of all plant cells. Chloroplast genomes -- likely vestiges of ancestral bacteria -- are organized into DNA-protein complexes called nucleoids. While significant work has been done to understand the dynamics of DNA in the nuclei of plant cells, little is known about the dynamics of chloroplast nucleoids. Now Yusuke Kobayashi, PhD, and Yoshiki Nishimura, PhD, of Kyoto University, Osami Misumi, PhD, of Yamaguchi University, and other collaborators have isolated and characterized a protein in chloroplasts that is essential for proper nucleoid segregation. Their findings were published online on May 11, 2017 in Science. The article is titled "Holliday-Junction Resolvases Mediate Chloroplast Nucleoid Segregation.” "To understand the dynamics of chloroplast nucleoids, we focused on their behavior during chloroplast division in the green alga Chlamydomonas reinhardtii," explains Dr. Nishimura. "We screened about 6,000 specimens with random mutations in their DNA and then isolated the ones with defective nucleoid segregation." One of these mutants was found to have a defect in a gene the team calls moc1, for "monokaryotic chloroplast 1". The chloroplasts in this mutant possessed only a single nucleoid, and showed unequal segregation during chloroplast division. A homologous moc1 gene was then found in a land plant commonly used for research, Arabidopsis thaliana. When mutated, the researchers discovered that these organisms exhibit growth defects and abnormal nucleoid segregation.

New Lung “Organoids” Mimic Features of Full-Size Lung; Mini-Organs May Aid In Understanding, Treating Respiratory Diseases

New lung "organoids"--tiny 3-D structures that mimic features of a full-sized lung--have been created from human pluripotent stem cells by researchers at the Columbia University Medical Center (CUMC). The team used the organoids to generate models of human lung diseases in a lab dish, models that could be used to advance our understanding of a variety of respiratory diseases. A paper detailing the discovery was published online on April 24, 2017 in Nature Cell Biology. The article is titled “A Three-Dimensional Model of Human Lung Development and Disease from Pluripotent Stem Cells.” Organoids are 3-D structures containing multiple cell types that look and function like a full-sized organ. By reproducing an organ in a dish, researchers hope to develop better models of human diseases, and find new ways of testing drugs and regenerating damaged tissue. "Researchers have taken up the challenge of creating organoids to help us understand and treat a variety of diseases," said Hans-Willem Snoeck, PhD, Professor of Medicine (in Microbiology & Immunology) at CUMC and lead investigator of the study. "But we have been tested by our limited ability to create organoids that can replicate key features of human disease." The lung organoids created in Dr. Snoeck's lab are the first to include branching airway and alveolar structures, similar to those in human lungs. To demonstrate their functionality, the researchers showed that the organoids reacted in much the same way as a real lung does when infected with respiratory syncytial virus (RSV). Additional experiments revealed that the organoids also responded as a human lung would when carrying a gene mutation linked to pulmonary fibrosis. RSV is a major cause of lower respiratory tract infection in infants and has no vaccine or effective antiviral therapy.

Fittest Tasmanian Devils Are Most Likely to Be Infected with Transmissible Facial Tumor Disease

Research published online on May 10, 2017 in Ecology Letters, shows that Tasmanian devils that catch devil facial tumor disease (DFTD) have higher survival and reproductive rates prior to disease-induced death than individuals that do not become infected. The article is titled “Infection of the Fittest: Devil Facial Tumor Disease Has Greatest Effect on Individuals with Highest Reproductive Output.” Typically infectious diseases affect mostly older, younger, or less healthy individuals. However, a team of scientists from Australia and the US, led by Dr. Konstans Wells of Griffith's Environmental Futures Research Institute (EFRI), found that devils with higher fitness are at highest risk of infection and death from facial tumors. Dr. Wells said this was probably because of the disease's mode of transmission among socially dominant individuals. "It's an important finding, as it indicates that the fittest devils, which are the ones typically engaging in mating or aggressive behavior, are at highest risk to acquire tumors," he said. Devil facial tumor disease - a proliferating cell line that grows into deadly tumors - is among only a few known cases of transmissible cancer and is believed to be transmitted when devils bite each other. Ten years of intensive field surveys of devils collected by study authors Dr. Rodrigo Hamede and Associate Professor Menna Jones of the University of Tasmania, combined with a novel statistical modelling approach to assess infection dynamics and tumor growth, led to the findings. Senior author Professor Hamish McCallum, also from EFRI, said the findings contradicted conventional wisdom that infection of relatively weakened individuals was commonplace in the spread and persistence of diseases.