Endogenous Mammalian Cardiotonic Steroids—A New Cardiovascular Risk Factor?—A Mini-Review

The role of endogenous mammalian cardiotonic steroids (CTS) in the physiology and pathophysiology of the cardiovascular system and the kidneys has interested researchers for more than 20 years. Cardiotonic steroids extracted from toads or plants, such as digitalis, have been used to treat heart disease since ancient times. CTS, also called endogenous digitalis-like factors, take part in the regulation of blood pressure and sodium homeostasis through their effects on the transport enzyme called sodium–potassium adenosine triphosphatase (Na/K-ATPase) in renal and cardiovascular tissue. In recent years, there has been increasing evidence showing deleterious effects of CTS on the structure and function of the heart, vasculature and kidneys. Understanding the role of CTS may be useful in the development of potential new therapeutic strategies.

RNA N6-Methyladenosine Responds to Low-Temperature Stress in Tomato Anthers

Cold stress is a serious threat to subtropical crop pollen development and induces yield decline. N6-methyladenosine (m6A) is the most frequent mRNA modification and plays multiple physiological functions in plant development. However, whether m6A regulates pollen development is unclear, and its putative role in cold stress response remains unknown. Here, we observed that moderate low-temperature (MLT) stress induced pollen abortion in tomato. This phenotype was caused by disruption of tapetum development and pollen exine formation, accompanied by reduced m6A levels in tomato anther. Analysis of m6A-seq data revealed 1,805 transcripts displayed reduced m6A levels and 978 transcripts showed elevated m6A levels in MLT-stressed anthers compared with those in anthers under normal temperature. These differentially m6A enriched transcripts under MLT stress were mainly related to lipid metabolism, adenosine triphosphatase (ATPase) activity, and ATP-binding pathways. An ATP-binding transcript, SlABCG31, had significantly upregulated m6A modification levels, which was inversely correlated to the dramatically downregulated expression level. These changes correlated with higher abscisic acid (ABA) levels in anthers and disrupted pollen wall formation under low-temperature stress. Our findings characterized m6A as a novel layer of complexity in gene expression regulation and established a molecular link between m6A methylation and tomato anther development under low-temperature conditions.

Mitochondrial content and oxidative damage in full-term placentas from SGA, LGA and AGA infants pregnant women

IntroductionThe aim was to determine the mitochondrial content, oxidative and nitrosative status in placentas from pregnant women who delivery newborns with alteration of intrauterine growth.Material and methodsPlacentas were selected because the newborns were classified as small for gestational age (SGA, lowest 10th percentile; n = 9), appropriate for gestational age (AGA; n = 9) and large for gestational age (LGA, tallest 90th percentile; n = 9). In the placenta tissue oxidative and nitrosative status, and the mitochondrial content were determined.ResultsLipid peroxidation (TBARS) levels were higher in LGA placentas compared with SGA placentas, but not compared with AGA placentas. Carbonyl levels were higher in LGA placentas compared with the AGA and SGA placentas. The 3-nitrotyrosine (3-NT)/actin ratio was higher in the SGA and LGA placentas than in AGA placentas. Moreover, AGA placentas did have higher cytochrome oxidase (COX4)/actin ratio compared with the SGA and LGA placentas. The AMP–activated protein kinase alpha (AMPK/actin ratio was significantly lower in placentas from SGA compared with the placentas from AGA and LGA. With respect to the adenosine triphosphatase (ATPase) activity, this was significantly lower in placentas from LGA compared with the placentas from AGA and SGA.ConclusionsThe placentas of LGA newborns have higher oxidized lipid and protein levels, whereas SGA and LGA placentas have higher nitrosative damage levels than the AGA placentas; the present data also suggest that the mitochondrial content is lower in SGA and LGA placentas than in AGA placentas.

EFFECT OF AFLATOXIN B-CONTAMINATED FEED ON GOAT ERYTHROCYTE MEMBRANE CALCIUM ADENOSINE TRIPHOSPHATASE IN VITRO

Aflatoxin B1 (AFBI) 2, a food/feed contaminant in the tropics, stimulated the activity of gout erythrocyte membrane ion motive calcium adenosine triphosphatase (Ca-ATPase). The stimulatory action was concentration-dependent, typical of a saturation kinetic effect. The degree of stimulation varied from 20% to more than 90% between the lowest (0.1 M) and highest (1000 M) contentrations. AFB1 induced changes in the apparent kinetic parameters, Km and Vmax, of the erythrocyte membrane-bound enzyme. This could affect erythrocyte structure, and thus, the erythrocyte function in oxygen and delivery to the cells.

Piwi suppresses transcription of Brahma-dependent transposons via Maelstrom in ovarian somatic cells

Drosophila Piwi associates with PIWI-interacting RNAs (piRNAs) and represses transposons transcriptionally through heterochromatinization; however, this process is poorly understood. Here, we identify Brahma (Brm), the core adenosine triphosphatase of the SWI/SNF chromatin remodeling complex, as a new Piwi interactor, and show Brm involvement in activating transcription of Piwi-targeted transposons before silencing. Bioinformatic analyses indicated that Piwi, once bound to target RNAs, reduced the occupancies of SWI/SNF and RNA polymerase II (Pol II) on target loci, abrogating transcription. Artificial piRNA-driven targeting of Piwi to RNA transcripts enhanced repression of Brm-dependent reporters compared with Brm-independent reporters. This was dependent on Piwi cofactors, Gtsf1/Asterix (Gtsf1), Panoramix/Silencio (Panx), and Maelstrom (Mael), but not Eggless/dSetdb (Egg)–mediated H3K9me3 deposition. The λN-box B–mediated tethering of Mael to reporters repressed Brm-dependent genes in the absence of Piwi, Panx, and Gtsf1. We propose that Piwi, via Mael, can rapidly suppress transcription of Brm-dependent genes to facilitate heterochromatin formation.

Steps toward translocation-independent RNA polymerase inactivation by terminator ATPase ρ

Factor-dependent transcription termination mechanisms are poorly understood. We determined a series of cryo–electron microscopy structures portraying the hexameric adenosine triphosphatase (ATPase) ρ on a pathway to terminating NusA/NusG-modified elongation complexes. An open ρ ring contacts NusA, NusG, and multiple regions of RNA polymerase, trapping and locally unwinding proximal upstream DNA. NusA wedges into the ρ ring, initially sequestering RNA. Upon deflection of distal upstream DNA over the RNA polymerase zinc-binding domain, NusA rotates underneath one capping ρ subunit, which subsequently captures RNA. After detachment of NusG and clamp opening, RNA polymerase loses its grip on the RNA:DNA hybrid and is inactivated. Our structural and functional analyses suggest that ρ, and other termination factors across life, may use analogous strategies to allosterically trap transcription complexes in a moribund state.

Mechanism of spliceosome remodeling by the ATPase/helicase Prp2 and its coactivator Spp2

Spliceosome remodeling, executed by conserved adenosine triphosphatase (ATPase)/helicases including Prp2, enables precursor messenger RNA (pre-mRNA) splicing. However, the structural basis for the function of the ATPase/helicases remains poorly understood. Here, we report atomic structures of Prp2 in isolation, Prp2 complexed with its coactivator Spp2, and Prp2-loaded activated spliceosome and the results of structure-guided biochemical analysis. Prp2 weakly associates with the spliceosome and cannot function without Spp2, which stably associates with Prp2 and anchors on the spliceosome, thus tethering Prp2 to the activated spliceosome and allowing Prp2 to function. Pre-mRNA is loaded into a featured channel between the N and C halves of Prp2, where Leu536 from the N half and Arg844 from the C half prevent backward sliding of pre-mRNA toward its 5′-end. Adenosine 5′-triphosphate binding and hydrolysis trigger interdomain movement in Prp2, which drives unidirectional stepwise translocation of pre-mRNA toward its 3′-end. These conserved mechanisms explain the coupling of spliceosome remodeling to pre-mRNA splicing.