Frontiers in Biology

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Intracellular trafficking of planar cell polarity proteins
Yan Huang, Tianji Ma, Yusong Guo
Front. Biol.    2018, 13 (6): 395-405.
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BACKGROUND: Planar cell polarity (PCP) is a phenomenon in which epithelial cells are polarized along the plane of a tissue. PCP is critical for a variety of developmental processes and is regulated by a set of evolutionarily conserved PCP signaling proteins. Many of the PCP proteins adopt characteristic asymmetric localizations on the opposing cellular boundaries. Currently, the molecular mechanisms that establish and maintain this PCP asymmetry remain largely unclear. Newly synthesized integral PCP proteins are transported along the secretory transport pathway to the plasma membranes. Once delivered to the plasma membranes, PCP proteins undergo endocytosis. Recent studies reveal insights into the intracellular trafficking of PCP proteins, suggesting that intracellular trafficking of PCP proteins contributes to establishing the PCP asymmetry.

OBJECTIVE: To understand the intracellular trafficking of planar cell polarity proteins in the secretory transport pathway and endocytic transport pathway.

METHODS: This review summarizes our current understanding of the intracellular trafficking of PCP proteins. We highlights the molecular mechanisms that regulate sorting of PCP proteins into transport vesicles and how the intracellular trafficking process regulates the asymmetric localizations of PCP proteins.

RESULTS: Current studies reveal novel insights into the molecular mechanisms mediating intracellular trafficking of PCP proteins. This process is critical for delivering newly synthesized PCP proteins to their specific destinations, removing the unstable or mislocalized PCP proteins from the plasma membranes and preserving tissue polarity during proliferation of mammalian skin cells.

CONCLUSION: Understanding how PCP proteins are delivered in the secretory and endocytic transport pathway will provide mechanistic insights into how the asymmetric localizations of PCP proteins are established and maintained.

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Androgen and estrogen receptors in placental physiology and dysfunction
Erin S McWhorter, Jennifer E Russ, Quinton A Winger, Gerrit J Bouma
Front. Biol.    2018, 13 (5): 315-326.
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BACKGROUND: The placenta is recognized as an endocrine organ, largely due to its secretions of steroid hormones, including progesterone, androgens, and estrogens. Steroid hormones play an essential role in the progression of pregnancy, fetal development, and growth. Furthermore, steroids are necessary for establishment and maintenance of a normal pregnancy, preparing the endometrium for implantation, stimulating endometrial secretions, and regulating uterine blood flow, however the exact mechanism of sex steroid signaling through their receptors in placental function is unknown.

OBJECTIVE: In this review, we will provide an overview of the current knowledge on sex steroid receptors in normal placental development, as well as evidence of abnormal signaling associated with placental dysfunction.

METHODS: A systematic literature search was performed using the NCBI PubMed search engine, including the following key works: estrogen receptor, androgen receptor, placenta, placental development, cytotrophoblast, and differentiation.

RESULTS: Of the over 700 articles that were returned, 125 studies focused on estrogen and androgen receptors in human placenta development and function during normal and abnormal pregnancy, as well as in rodents and ruminants placentae.

CONCLUSION: Receptors for both estrogens and androgens have been localized within the mammalian placenta, but surprisingly little is known about their signaling in trophoblast cell differentiation and function. An emerging picture is developing in which estrogen receptors possibly play role in cytotrophoblast proliferation and extravillous trophoblast invasion, whereas androgen receptors are involved in syncytiotrophoblast differentiation and function.

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Signal integration in the (m)TORC1 growth pathway
Kailash Ramlaul, Christopher H. S. Aylett
Front. Biol.    2018, 13 (4): 237-262.
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BACKGROUND: The protein kinase Target Of Rapamycin (TOR) is a nexus for the regulation of eukaryotic cell growth. TOR assembles into one of two distinct signalling complexes, TOR complex 1 (TORC1) and TORC2 (mTORC1/2 in mammals), with a set of largely non-overlapping protein partners. (m)TORC1 activation occurs in response to a series of stimuli relevant to cell growth, including nutrient availability, growth factor signals and stress, and regulates much of the cell’s biosynthetic activity, from proteins to lipids, and recycling through autophagy. mTORC1 regulation is of great therapeutic significance, since in humans many of these signalling complexes, alongside subunits of mTORC1 itself, are implicated in a wide variety of pathophysiologies, including multiple types of cancer, neurological disorders, neurodegenerative diseases and metabolic disorders including diabetes.

METHODOLOGY: Recent years have seen numerous structures determined of (m)TOR, which have provided mechanistic insight into (m)TORC1 activation in particular, however the integration of cellular signals occurs upstream of the kinase and remains incompletely understood. Here we have collected and analysed in detail as many as possible of the molecular and structural studies which have shed light on (m)TORC1 repression, activation and signal integration.

CONCLUSIONS: A molecular understanding of this signal integration pathway is required to understand how (m)TORC1 activation is reconciled with the many diverse and contradictory stimuli affecting cell growth. We discuss the current level of molecular understanding of the upstream components of the (m)TORC1 signalling pathway, recent progress on this key biochemical frontier, and the future studies necessary to establish a mechanistic understanding of this master-switch for eukaryotic cell growth.

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Siberian plants: untapped repertoire of bioactive endosymbionts
Syed Baker, Svetlana V. Prudnikova, Tatiana Volova
Front. Biol.    2018, 13 (3): 157-167.
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BACKGROUND: Endosymbionts are microorganisms present in all plant species, and constitute the subject of interest among the scientific community. These symbionts have gained considerable attention in recent years, owing to their emerging biological roles. Global challenges, such as antimicrobial resistance, treatment of infectious diseases such as HIV and tuberculosis, cancer, and many genetic disorders, exist. Endosymbionts can help address these challenges by secreting value-added bioactive compounds with various activities.

OBJECTIVE: Herein, we describe the importance of plants inhabiting Siberian niches. These plants are considered to be among the least studied organisms in the plant kingdom worldwide. Barcoding these plants can be of interest for exploring bioactive endosymbionts possessing myriad biological properties.

METHODS: A systematic survey of relevant scientific reports was conducted using the PubMed search engine. The reports were analyzed, and compiled to draft this review.

RESULTS: The literature survey on Siberian plants regarding endosymbionts included a few reports, since extremely few exploratory studies have been conducted on the plants in these regions. Studies on the endosymbionts of these plants are highly valuable, as they report potent endosymbionts possessing numerous biological properties. Based on these considerations, this review aims to create awareness among the global scientific community working on related areas.

CONCLUSION: This review could provide the basis for barcoding novel endosymbionts of Siberian plants and their ecological importance, which can be exploited in various sectors. The main purpose of this review is to create awareness of Siberian plants, which are among the least studied organisms in the plant kingdom, with respect to endosymbionts, among the scientific community.

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An overview of pyrethroid insecticides
Anudurga Gajendiran, Jayanthi Abraham
Front. Biol.    2018, 13 (2): 79-90.
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BACKGROUND: Pesticides are used to control various pests of agricultural crops worldwide. Despite their agricultural benefits, pesticides are often considered a serious threat to the environment because of their persistence. Pyrethroids are synthetic derivates of pyrethrins, which are natural organic insecticides procured from the flowers of Chrysanthemum cinerariaefolium and C. coccineum. Pyrethroids are classified into two groups—class I and class II—based on their toxicity and physical properties. These pyrethroids are now used in many synthetic insecticides and are highly specific against insects; they are generally used against mosquitoes. The prominent site of insecticidal action of pyrethroids is the voltage-sensitive sodium channels.

METHODS and RESULTS: Pyrethroids are found to be stable, and they persist in the environment for a long period. This article provides an overview of the different classes, structure, and insecticidal properties of pyrethroid. Furthermore, the toxicity of pyrethroids is also discussed with emphasis on bioremediation to alleviate pollution.

CONCLUSIONS: The article focuses on various microorganisms used in the degradation of pyrethroids, the molecular basis of degradation, and the role of carboxylesterase enzymes and genes in the detoxification of pyrethroid.

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RNA-dependent pseudouridylation catalyzed by box H/ACA RNPs
Meemanage D. De Zoysa, Yi-Tao Yu
Front. Biol.    2018, 13 (1): 1-10.
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BACKGROUND: Pseudouridine (Y) is the most abundant post-transcriptionally modified nucleotide found in RNA. Y is clustered in functionally important and evolutionary conserved regions of RNAs in all three domains of life. Pseudouridylation is catalyzed by two distinct mechanisms: an RNA-independent and an RNA-dependent mechanism. The former involves a group of stand-alone protein enzymes, and the latter involves a family of complex enzymes called box H/ACA RNPs, each of which consists of one RNA (box H/ACA RNA) and a set of four core proteins. Over the years, the mechanism of RNA-dependent pseudouridylation has been extensively studied. The crystal structures of partial and complete box H/ACA RNP have been solved. However, the detailed picture of RNA-dependent pseudouridylation is still not entirely clear.

OBJECTIVE: In this work, we review what is known about box H/ACA RNP and the mechanism by which box H/ACA RNP catalyzes RNA-dependent pseudouridylation. We also discuss some examples of the dual nature and redundancy of box H/ACA RNPs that deviate from the usual mechanism.

METHODS: A methodical literature search was performed using the Pubmed central search engine and International Digital Publishing Forum (EPUB) using the following keywords: “pseudouridylation,” “pseudouridine,” and “box H/ACA RNP.” The necessary information was extracted and cited.

RESULTS: A detailed introduction is made including the discovery, mechanism and crystal structure of box H/ACA RNP. Three sequence/structural requirements for box H/ACA RNA-guided pseudouridylation are discussed and the exceptions to those rules are explored.

CONCLUSION: Over the years, box H/ACA RNP-catalyzed pseudouridylation has been extensively studied, generating fruitful results. However, a detailed picture regarding the mechanism of this reaction is still to be deciphered. More work is needed to fully understand box H/ACA RNP-catalyzed pseudouridylation.

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High salt and fat intake, inflammation, and risk of cancer
Amir Abdoli
Front. Biol.    2017, 12 (6): 387-391.
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BACKGROUND: Inflammatory conditions are involved in the pathophysiology of cancer. Recent findings have revealed that excessive salt and fat intake is involved in the development of severe inflammatory reactions.

METHODS: A literature search was performed on various online databases (PubMed, Scopus, and Google Scholar) regarding the roles of high salt and fat intake in the induction of inflammatory reactions and their roles in the etiopathogenesis of cancer.

RESULTS: The results indicate that high salt and fat intake can induce severe inflammatory conditions. However, various inflammatory conditions have been strongly linked to the development of cancer. Hence, high salt and fat intake might be involved in the pathogenesis of cancer progression via putative mechanisms related to inflammatory reactions.

CONCLUSION: Reducing salt and fat intake may decrease the risk of cancer.

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Epigenetic regulators sculpt the plastic brain
Ji-Song Guan, Hong Xie, San-Xiong Liu
Front. Biol.    2017, 12 (5): 317-332.
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BACKGROUND: Epigenetic regulation is a level of transcriptional regulation that occurs in addition to the genetic programming found in biological systems. In the brain, the epigenetic machinery gives the system an opportunity to adapt to a given environment to help not only the individual but also the species survive and expand. However, such a regulatory system has risks, as mutations resulting from epigenetic regulation can cause severe neurological or psychiatric disorders.

OBJECTIVE: Here, we review the most recent findings regarding the epigenetic mechanisms that control the activity-dependent gene transcription leading to synaptic plasticity and brain function and the defects in these mechanisms that lead to neurological disorders.

METHODS: A search was carried out systematically, searching all relevant publications up to June 2017, using the PubMed search engine. The following keywords were used: “activity induced epigenetic,” “gene transcription,” and “neurological disorders.”

RESULTS: A wide range of studies focused on the roles of epigenetics in transgenerational inheritance, neural differentiation, neural circuit assembly and brain diseases. Thirty-one articles focused specifically on activity-induced epigenetic modifications that regulated gene transcription and memory formation and consolidation.

CONCLUSION: Activity-dependent epigenetic mechanisms of gene expression regulation contribute to basic neuronal physiology, and defects were associated with an elevated risk for brain disorders.

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Illuminating the structure and dynamics of chromatin by fluorescence labeling
Shipeng Shao, Lei Chang, Yingping Hou, Yujie Sun
Front. Biol.    2017, 12 (4): 241-257.
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BACKGROUND: Visualization of chromosomal loci location and dynamics is crucial for understanding many fundamental intra-nuclear processes such as DNA transcription, replication, and repair.

OBJECTIVE: Here, we will describe the development of fluorescence labeling methods for chromatin imaging, including traditional as well as emerging chromatin labeling techniques in both fixed and live cells. We will also discuss current issues and provide a perspective on future developments and applications of the chromatin labeling technology.

METHODS: A systematic literature search was performed using the PubMed. Studies published over the past 50 years were considered for review. More than 100 articles were cited in this review.

RESULTS: Taking into account sensitivity, specificity, and spatiotemporal resolution, fluorescence labeling and imaging has been the most prevalent approach for chromatin visualization. Among all the fluorescent labeling tools, the adoption of genome editing tools, such as TALE and CRISPR, have great potential for the labeling and imaging of chromatin.

CONCLUSION: Although a number of chromatin labeling techniques are available for both fixed and live cells, much more effort is still clearly required to develop fluorescence labeling methods capable of targeting arbitrary sequences non-intrusively to allow long-term, multiplexing, and high-throughput imaging of genomic loci and chromatin structures. The emerging technological advances will outline a next-generation effort toward the comprehensive delineation of chromatin at single-cell level with single-molecule resolution.

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PTEN at the interface of immune tolerance and tumor suppression
Andrew Brandmaier, Sheng-Qi Hou, Sandra Demaria, Silvia C. Formenti, Wen H. Shen
Front. Biol.    2017, 12 (3): 163-174.
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BACKGROUND: PTEN is well known to function as a tumor suppressor that antagonizes oncogenic signaling and maintains genomic stability. ThePTEN gene is frequently deleted or mutated in human cancers and the wide cancer spectrum associated with PTEN deficiency has been recapitulated in a variety of mouse models ofPten deletion or mutation. Pten mutations are highly penetrant in causing various types of spontaneous tumors that often exhibit resistance to anticancer therapies including immunotherapy. Recent studies demonstrate that PTEN also regulates immune functionality.

OBJECTIVE: To understand the multifaceted functions of PTEN as both a tumor suppressor and an immune regulator.

METHODS: This review will summarize the emerging knowledge of PTEN function in cancer immunoediting. In addition, the mechanisms underlying functional integration of various PTEN pathways in regulating cancer evolution and tumor immunity will be highlighted.

RESULTS: Recent preclinical and clinical studies revealed the essential role of PTEN in maintaining immune homeostasis, which significantly expands the repertoire of PTEN functions. Mechanistically, aberrant PTEN signaling alters the interplay between the immune system and tumors, leading to immunosuppression and tumor escape.

CONCLUSION: Rational design of personalized anti-cancer treatment requires mechanistic understanding of diverse PTEN signaling pathways in modulation of the crosstalk between tumor and immune cells.

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