Transcriptional activity and epigenetic regulation of transposable elements in the symbiotic fungus Rhizophagus irregularis

Arbuscular mycorrhizal (AM) fungi form mutualistic relationships with most land plant species. AM fungi have long been considered as ancient asexuals. Long-term clonal evolution would be remarkable for a eukaryotic lineage and suggests the importance of alternative mechanisms to promote genetic variability facilitating adaptation. Here, we assessed the potential of transposable elements for generating such genomic diversity. The dynamic expression of TEs during Rhizophagus irregularis spore development suggests ongoing TE activity. We find Mutator-like elements located near genes belonging to highly expanded gene families. Whole-genome epigenomic profiling of R. irregularis provides direct evidence of DNA methylation and small RNA production occurring at TE loci. Our results support a model in which TE activity shapes the genome, while DNA methylation and small RNA–mediated silencing keep their overproliferation in check. We propose that a well-controlled TE activity directly contributes to genome evolution in AM fungi.

The arbuscular mycorrhizal (AM) symbiosis is hundreds of millions of years old and a majority of the world''s plant species are hosts to AM fungi (AMF) (Lutzoni et al. 2018). As such, these fungi exist in a wide range of environments and can even engage in symbioses with multiple plant species simultaneously. The complex life cycles of AMF suggest a requirement for strong developmental and phenotypic plasticity. However, although AMF carry meiosis-related genes (Halary et al. 2011) and heterokaryotic strains originating from two parental strains have been described (Ropars et al. 2016), genetically distinct strains as a product of meiosis have never been reported and direct evidence of sexual reproduction is lacking (den Bakker et al. 2010; Chen et al. 2018b; Reinhardt et al. 2021). This has led to the hypothesis that AMF are ancient asexual organisms, which raises a key question on how these fungi were able to diversify their gene inventory and fill such varied ecological niches.Genome assemblies are available for a number of AMF species, including the model Rhizophagus irregularis (Tisserant et al. 2013; Chen et al. 2018a; Maeda et al. 2018). Genomic analyses of AMF have revealed contents of repetitive sequences ranging from 23% to 43% (Chen et al. 2018a; Morin et al. 2019). These repeats consist of transposable elements (TEs) and expanded gene families that occasionally form tandemly repeated arrays of duplicate genes (Tisserant et al. 2013; Chen et al. 2018a; Maeda et al. 2018; Morin et al. 2019; Silvestri et al. 2019, 2020). Expanded family genes are either orphans (no significant homolog can be identified) or contain protein domains related to signaling and RNA interference (RNAi), such as kinase domains, BTB/POZ (Broad-Complex, Tramtrack and Bric-a-brac/Poxvirus and Zinc finger) domains, Sel1-like tetratricopeptide repeats, and Kelch-like and P-element Induced WImpy testis (PIWI) domains. These high copy number genes form strain-specific accessory gene sets and have been proposed to play roles in perception and interaction with the environment (Reinhardt et al. 2021).Transposons are repetitive DNA sequences that colonize genomes and generate intra- and inter-specific genetic variability. By moving and replicating within genomes, TEs cause chromosomal rearrangements and compartmentalization, deletions, duplications, and regulatory changes (Chuong et al. 2017). As their roles can be adaptive as well as deleterious, eukaryotes have developed defense mechanisms to control their proliferation. Three mechanisms of defense have been described in fungi: repeat-induced point mutation (RIP) (Gladyshev 2017), DNA cytosine methylation (Bewick et al. 2019), and RNAi (Torres-Martínez and Ruiz-Vázquez 2017). Signatures of RIP have not been detected in the AMF Gigaspora margarita or in species of the Mucoromycotina, a sister subphylum to the Glomeromycotina to which AMF belong (Venice et al. 2020). However, the presence of DNA cytosine methyltransferases and RNAi pathway genes encoded in AM genomes suggests their role in TE silencing.The genomic organization of TEs in AMF is still largely unknown, as are the mechanisms that keep them under control. In this study, we investigate the organization of TEs, genes, DNA methylation, and RNAi on a global genome level in the model AMF R. irregularis.     

Pharmacokinetic/pharmacodynamic modelling of the eosinopenic and hypokalemic effects of formoterol and theophylline combination in healthy men.

Interactions of formoterol and theophylline were evaluated with the use of pharmacokinetic-pharmacodynamic (PK/PD) modelling. Oral doses of 144 microg of formoterol and 375 mg of theophylline were given separately or combined to healthy subjects. As effect parameters, plasma eosinophil and potassium concentrations were used. Kinetic interactions between formoterol and theophylline were not found. Plasma drug concentrations were linked to the observed effects via an effect compartment model with a sigmoid E max model. The E max values+/-SD for the hypokalemic effects were 2.29+/-0.78 mmol/l for formoterol and 1.64+/-1.16 mmol/l for theophylline (P>0.05). The E max values for the eosinopenic effects were fixed at zero. The EC 50 values of the eosinopenic and hypokalemic effects were respectively 91.4+/-38.2 pg/ml and 128.4+/-52.9 pg/ml for formoterol, and 11. 9+/-4.6 microg/ml and 15.5+/-4.8 microg/ml for theophylline. Effects of both drugs combined were described with a non-competitive interaction model. The correlation coefficients of the fits of the eosinopenic and hypokalemic effects were respectively 0.9520+/-0. 0311 and 0.9371+/-0.0227, supporting our hypothesis of non-competitive interaction.     

Evolution of graft morphology and function after recellularization of decellularized rat livers

Decellularization of livers is a well‐established procedure. Data on different reseeding techniques or the functional evolution and reorganization processes of repopulated grafts remains limited. A proprietary, customized bioreactor was established to repopulate decellularized rat livers (n = 21) with primary rat hepatocytes (150 × 10⁶ cells) via the hepatic artery and to subsequently evaluate graft morphology and function during 7 days of ex vivo perfusion. Grafts were analysed at 1 h, 6 h, 12 h, 24 h, 3 days, 5 days and 7 days after recellularization (all n = 3) by immunohistological evaluation, hepatocyte‐related enzyme (aspartate transaminase, alanine transaminase and lactate dehydrogenase) and albumin measurement in the perfusate. This appears to be the first available protocol for repopulation of rat livers via the hepatic artery. Within the first 24 h after repopulation, the hepatocytes seemed to migrate out of the vascular network and form clusters in the parenchymal space around the vessels. Graft function increased for the first 24 h after repopulation with a significantly higher function compared to standard two‐dimensional culture after 24 h. Thereafter, graft function constantly decreased with significantly lower values after 6 days and 7 days of perfusion, although histologically viable hepatocytes were found even after this period. The data suggests that, owing to a constant loss of function, repopulated grafts should potentially be implanted as soon as cell engraftment and graft re‐organization are completed. Copyright © 2016 John Wiley & Sons, Ltd.     

Is standard-echocardiography sufficient for identification of responders?

During recent years cardiac re-synchronization has become an important tool in the treatment of patients with signs and symptoms of heart failure and de-synchronized contraction of the heart. This article describes the pathophysiological basis of de-synchronized contraction due to left bundle branch block and the use of conventional echocardiography to unmask whether the electrical abnormality is accompanied by an asynchronous contraction in the individual patient. The altered contraction in the de-synchronized heart is analysed on different levels: atrioventricular dyssynchrony describes the disturbed mechanical coupling of the ventricles and atria, interventricular dyssynchrony describes the disturbed mechanical coupling of the left and right ventricle, and intraventricular dyssynchrony describes the uncoordinated contraction of the left ventricle. Since tissue Doppler imaging is implemented only in the top level echo machines of the respective manufacturers, this article uses parameters derived from standard echo techniques to analyse the different aspects of dyssynchrony.     

Impairments in orienting to visual stimuli in monkeys following unilateral lesions of the superior sulcal polysensory cortex

Monkeys were tested for head and eye orientation to illuminated lamps in a hemisphere before and after serial, unilateral lesions of the polysensory superior temporal cortex (STS) or control lesions. Following STS lesions they were impaired in orienting to contralateral lamps; this impairment was more severe and persistent when a ipsilateral stimulus in the mirror-image position was simultaneously presented. These findings, together with deficits in manual reaching and grasping observed following STS lesions, support the view that the STS is part of a polysensory system controlling attention and exploratory movements.     

Gender hierarchies in the health labor force

Rapid growth and increasing diversity characterize trends of the U.S. health labor force in recent decades. While these trends have promoted change on many different fronts of the health system, hierarchical organization of the health work force remains intact. Workers continue to be stratified by class and race. Superimposed on both strata is a structure that segregates jobs by gender, between and within health occupations. While female health workers outnumber males by three to one, they remain clustered in jobs and occupations lower in pay, less prestigious, and less autonomous than those of their male counterparts. What has prevented women from improving their economic and leadership status as health workers? Is work performed by men of higher prestige because men perform it? Would curative and technical fields have less status if dominated by women? Would health promotion be funded more generously if most health educators were men? In this article, two analytical constructs are presented to take a closer look at occupational categories, selected structural characteristics, differential rewards, and their relationship to gender segregation. Taken together, they demonstrate how women always cluster at the bottom and men at the top, no matter which dimension is chosen.