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Archive - Dec 30, 2017

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Unlocking Mystery of Pollen Tube Guidance to the Ovule; Solving Crystal Structure of Pollen Tube Attractant (LURE) and Its Receptor (PRK6) May Provide Basis for Generation of Specifically Designed Cross-Breeding Plant Species

Fertilization in flowering plants occurs by the delivery of sperm cells to the ovule by the precise growth of pollen tubes from pollen. Pollen tube guidance plays a crucial role in controlling the growth of pollen tubes and a pollen tube attractant peptide LURE is secreted from the synergid cells next to the egg cell within the ovule to lead to successful fertilization. LURE is specific to each plant species and is therefore responsible for the fertilization between the same species. LURE1 has already been identified in a model plant Arabidopsis thaliana, and there have been reports on the presence of receptors on the pollen tube responsible for detecting LURE1. The key and lock model illustrates the relationship between the LURE peptide (ligand) and its receptor. To which lock (receptor) the key (LURE) binds and how it does so has been a mystery up to now. In order to identify the exact receptor on the pollen tube for LURE, Dr. Tetsuya Higashiyama, a professor at Nagoya University and his collaborators at Tsinghua University who have expertise in structural biology of plant ligands and receptors, performed analyses of the complexes by X-ray crystallography. The team examined the protein that binds to LURE by making LURE of Arabidopsis thaliana and its protein receptor by cultures of insect cells. As a result, they were able to determine that LURE specifically binds to a protein receptor called PRK6 (pollen receptor-like kinase 6) on the pollen tube. The results of this study were published online on November 6, 2017 in Nature Communications. The open-access article is titled “Structural Basis for Receptor Recognition of Pollen Tube Attraction Peptides.” The research team succeeded in obtaining and analyzing the crystal structure of LURE bound to the PRK6 receptor.

Trace Element Selenium Is an Essential Factor for Postnatal Development of Specific Type of Interneuron

Exactly 200 years ago, the Swedish scientist Jöns Jacob Berzelius discovered the trace element selenium, which he named after the goddess of the moon, Selene. Besides its industrial applications (chemical industry, production of semiconductors and toners), selenium is an essential trace element and indispensable for humans, many animals, and some bacteria. A team led by Dr. Marcus Conrad, research group leader at the Institute of Developmental Genetics (IDG) at Helmholtz Zentrum München, showed for the first time why selenium is a limiting factor for mammals. The work was published online on December 28, 2017 in Cell. The article is titled “Selenium Utilization by GPX4 Is Required to Prevent Hydroperoxide-Induced Ferroptosis.” For years, scientists have been investigating the processes of a novel type of cell death, known as ferroptosis. In this context, the enzyme GPX4, which normally contains selenium in the form of the amino acid selenocysteine, plays an important role. “In order to better understand the role of GPX4 in this death process, we established and studied mouse models in which the enzyme was modified," said study leader Dr. Conrad. "In one of these models, we observed that mice with a replacement of selenium to sulfur in GPX4 did not survive for longer than three weeks due to neurological complications." In their search for the underlying reasons, the researchers identified a distinct subpopulation of specialized neurons in the brain, which were absent when selenium-containing GPX4 was lacking. "In further studies, we were able to show that these neurons were lost during postnatal development, when sulfur- instead of selenium-containing GPX4 was present," stated first author of the study, Irina Ingold.

Cancer Cells Use Unfolded Protein Response (UPR) to Manipulate Circadian Clock in Ways That Allow Them to Survive Conditions That Are Toxic to Normal Cells

Tumor cells use the unfolded protein response to alter circadian rhythm, which contributes to more tumor growth, Hollings Cancer Center researchers at the Medical University of South Carolina (MUSC) have found. A key part of the circadian clock opposes this process, according to a paper published online on December 11, 2017 in Nature Cell Biology. The article is titled “A PERK–miR-211 Axis Suppresses Circadian Regulators and Protein Synthesis to Promote Cancer Cell Survival.” For tumors to grow and spread, cancer cells must make larger than normal amounts of nucleic acids and protein, so they can replicate themselves. Yet, in both normal and cancer cells that increase their synthesis of protein, a small percent of those proteins do not fold properly. When that happens, the cell activates its unfolded protein response (UPR), which slows down the making of new proteins while the misfolded proteins are refolded. Eventually, the buildup of misfolded proteins becomes toxic and leads to cell death. However, cancer cells have learned to use the UPR to slow protein synthesis when needed, in order to handle the backlog of misfolded proteins. This helps them survive in conditions that would kill normal cells. This pattern of adaptation is often seen in tumor cells, according to J. Alan Diehl, PhD, the SmartState Endowed Chair in Lipidomics, Pathobiology, and Therapy at the MUSC Hollings Cancer Center and senior researcher on the project. "What a tumor cell is doing is taking a pathway that's already in the cell and using it to its advantage," said Dr. Diehl. Yet it was not clear exactly how cancer cells were able to use UPR activity to influence circadian rhythm. Dr.