Evolutionarily Conserved 5’-3’ Exoribonuclease Xrn1 Accumulates at Plasma Membrane-Associated Eisosomes in Post-Diauxic Yeast

Regulation of gene expression on the level of translation and mRNA turnover is widely conserved evolutionarily. We have found that the main mRNA decay enzyme, exoribonuclease Xrn1, accumulates at the plasma membrane-associated eisosomes after glucose exhaustion in a culture of the yeast S. cerevisiae. Eisosomal localization of Xrn1 is not achieved in cells lacking the main component of eisosomes, Pil1, or Sur7, the protein accumulating at the membrane compartment of Can1 (MCC) - the eisosome-organized plasma membrane microdomain. In contrast to the conditions of diauxic shift, when Xrn1 accumulates in processing bodies (P-bodies), or acute heat stress, in which these cytosolic accumulations of Xrn1 associate with eIF3a/Rpg1-containing stress granules, Xrn1 is not accompanied by other mRNA-decay machinery components when it accumulates at eisosomes in post-diauxic cells. It is important that Xrn1 is released from eisosomes after addition of fermentable substrate. We suggest that this spatial segregation of Xrn1 from the rest of the mRNA-decay machinery reflects a general regulatory mechanism, in which the key enzyme is kept separate from the rest of mRNA decay factors in resting cells but ready for immediate use when fermentable nutrients emerge and appropriate metabolism reprogramming is required. In particular, the localization of Xrn1 to the eisosome, together with previously published data, accents the relevance of this plasma membrane-associated compartment as a multipotent regulatory site.     

Biochemical,Histopathological and Morphological Profiling of a Rat Model of Early Immune Stimulation: Relation to Psychopathology

Perinatal immune challenge leads to neurodevelopmental dysfunction, permanent immune dysregulation and abnormal behaviour, which have been shown to have translational validity to findings in human neuropsychiatric disorders (e.g. schizophrenia, mood and anxiety disorders, autism, Parkinson’s disease and Alzheimer’s disease). The aim of this animal study was to elucidate the influence of early immune stimulation triggered by systemic postnatal lipopolysaccharide administration on biochemical, histopathological and morphological measures, which may be relevant to the neurobiology of human psychopathology. In the present study of adult male Wistar rats we examined the brain and plasma levels of monoamines (dopamine, serotonin), their metabolites, the levels of the main excitatory and inhibitory neurotransmitters glutamate and γ-aminobutyric acid and the levels of tryptophan and its metabolites from the kynurenine catabolic pathway. Further, we focused on histopathological and morphological markers related to pathogenesis of brain diseases - glial cell activation, neurodegeneration, hippocampal volume reduction and dopaminergic synthesis in the substantia nigra. Our results show that early immune stimulation in adult animals alters the levels of neurotransmitters and their metabolites, activates the kynurenine pathway of tryptophan metabolism and leads to astrogliosis, hippocampal volume reduction and a decrease of tyrosine hydroxylase immunoreactivity in the substantia nigra. These findings support the crucial pathophysiological role of early immune stimulation in the above mentioned neuropsychiatric disorders.     

Ectopic expression of RNF168 and 53BP1 increases mutagenic but not physiological non-homologous end joining

DNA double strand breaks (DSBs) formed during S phase are preferentially repaired by homologous recombination (HR), whereas G₁ DSBs, such as those occurring during immunoglobulin class switch recombination (CSR), are repaired by non-homologous end joining (NHEJ). The DNA damage response proteins 53BP1 and BRCA1 regulate the balance between NHEJ and HR. 53BP1 promotes CSR in part by mediating synapsis of distal DNA ends, and in addition, inhibits 5’ end resection. BRCA1 antagonizes 53BP1 dependent DNA end-blocking activity during S phase, which would otherwise promote mutagenic NHEJ and genome instability. Recently, it was shown that supra-physiological levels of the E3 ubiquitin ligase RNF168 results in the hyper-accumulation of 53BP1/BRCA1 which accelerates DSB repair. Here, we ask whether increased expression of RNF168 or 53BP1 impacts physiological versus mutagenic NHEJ. We find that the anti-resection activities of 53BP1 are rate-limiting for mutagenic NHEJ but not for physiological CSR. As heterogeneity in the expression of RNF168 and 53BP1 is found in human tumors, our results suggest that deregulation of the RNF168/53BP1 pathway could alter the chemosensitivity of BRCA1 deficient tumors.     

Centric fusion polymorphism in captive animals of family Bovidae

Chromosomes of 228 captive specimens of the family Bovidae have been investigated. The examined animals were classified into the subfamilies Aepycerotinae, Reduncinae, Antilopinae, Alcelaphinae, Hippotraginae and Bovinae. Polymorphism for one fusion was identified in the species: Aepyceros melampus, 2n = 59–60; Redunca fulvorufula, 2n = 56–57; Kobus e. ellipsiprymnus, 2n = 50–52; Kobus e. defassa, 2n = 52–54 and Syncerus c. nanus, 2n = 54–55. This is the first study to reveal fusion 7;29 in Kobus e. defassa and simultaneously the respective polymorphism. Variation in the diploid number of chromosomes is also known in species: Oryx g. dammah and Oryx g. leucoryx but in this study only fusion 1;25 was identified in both karyotyped species. Our study showed that 13% of investigated individuals were polymorphic for the centric fusion and demonstrated the important role of cytogenetic screening in captive animals at zoological gardens.     

Recombination correlates with synaptonemal complex length and chromatin loop size in bovids—insights into mammalian meiotic chromosomal organization

Homologous chromosomes exchange genetic information through recombination during meiosis, a process that increases genetic diversity, and is fundamental to sexual reproduction. In an attempt to shed light on the dynamics of mammalian recombination and its implications for genome organization, we have studied the recombination characteristics of 112 individuals belonging to 28 different species in the family Bovidae. In particular, we analyzed the distribution of RAD51 and MLH1 foci during the meiotic prophase I that serve, respectively, as proxies for double-strand breaks (DSBs) which form in early stages of meiosis and for crossovers. In addition, synaptonemal complex length and meiotic DNA loop size were estimated to explore how genome organization determines DSBs and crossover patterns. We show that although the number of meiotic DSBs per cell and recombination rates observed vary between individuals of the same species, these are correlated with diploid number as well as with synaptonemal complex and DNA loop sizes. Our results illustrate that genome packaging, DSB frequencies, and crossover rates tend to be correlated, while meiotic chromosomal axis length and DNA loop size are inversely correlated in mammals. Moreover, axis length, DSB frequency, and crossover frequencies all covary, suggesting that these correlations are established in the early stages of meiosis.     

Birds girdling activity on exotic tree species as a form of adaptive behavior?

Four tree species in the Kostelec n. ?. l. arboretum (Czech Republic) have been repeatedly damaged by Dendrocopos medius. The unique aspect of this otherwise common behavior called girdling consists in regularly visiting the same trees every spring, although there are more than 1.200 tree species within the arboretum. We monitored transpiration, leaf phenology and the chemical composition of the xylem sap of girdled and nongirdled trees. Spectral analysis revealed slightly higher amounts of sugars, especially saccharose, in Cladrastis Raf. as the most regularly girdled tree among other conditions, comparing girdled to non-girdled trees. Higher transpiration rates were not confirmed in connection with girdling—quite the opposite—Cladrastis Raf. as the most highly favored tree for girdling showed the lowest transpiration rates (in average 6 kg water per day within spring months) compared to other non-girdled trees. We presume that the birds do not choose a particular tree on the basis of any visible or chemical traits but they examine many trees within their territory. Afterwards they probably remember the position of trees whose xylem sap starts to flow early in the spring compared to other trees, as their transpiration stream is enriched with sweet organic substances that represent an advantage for the forthcoming nesting period.     

Metagenome-derived haloalkane dehalogenases with novel catalytic properties

Applied Microbiology and Biotechnology - Haloalkane dehalogenases (HLDs) are environmentally relevant enzymes cleaving a carbon-halogen bond in a wide range of halogenated pollutants. PCR with...     

Phosphonate analogues of cyclopropavir phosphates and their E-isomers. Synthesis and antiviral activity

Z- and E-Phosphonate analogues 12 and 13 derived from cyclopropavir and the corresponding cyclic phosphonates 14 and 15 were synthesized and their antiviral activity was investigated. The 2,2-bis(hydroxymethylmethylenecyclopropane acetate (17) was transformed to tetrahydropyranyl acetate 18. Deacetylation gave intermediate 19 which was converted to bromide 20. Alkylation with diisopropyl methylphosphonate afforded after protecting group exchange (21 to 22) acetylated phosphonate intermediate 22. Addition of bromine gave the dibromo derivative 16 which was used in the alkylation–elimination procedure with 2-amino-6-chloropurine to give Z- and E-isomers 23 and 24. Hydrolytic dechlorination coupled with removal of all protecting groups gave the guanine phosphonates 12 and 13. Cyclization afforded the cyclic phosphonates 14 and 15. Z-Phosphonate 12 was a potent and non-cytotoxic inhibitor of human and murine cytomegalovirus (HCMV and MCMV) with EC₅₀ 2.2–2.7 and 0.13 μM, respectively. It was also an effective agent against Epstein-Barr virus (EBV, EC₅₀ 3.1 μM). The cyclic phosphonate 14 inhibited HCMV (EC₅₀ 2.4–11.5 μM) and MCMV (EC₅₀ 0.4 μM) but it was ineffective against EBV. Both phosphonates 12 and 14 were as active against two HCMV Towne strains with mutations in UL97 as they were against wild-type HCMV thereby circumventing resistance due to such mutations. Z-Phosphonate 12 was a moderate inhibitor of replication of herpes simplex virus types 1 and 2 (HSV-1 and HSV-2) but it was a potent agent against varicella zoster virus (VZV, EC₅₀ 2.9 μM). The cyclic phosphonate 14 lacked significant potency against these viruses. E-isomers 13 and 15 were devoid of antiviral activity.     

Tree growth and competition in a post-logging Quercus mongolica forest on Mt. Sobaek, South Korea

Secondary woodlands in South Korea cover most mountains from low to middle elevations. While general patterns of forest succession are well understood, little is known about mechanisms of stand recovery after disturbance. We examined the spatio-temporal variations in establishment, growth, size inequality, and mode of competition among trees in a 50-year-old post-logging Quercus mongolica-dominated stand. We further compared the growth and stem allometry of single trees, presumably of seed origin, with multi-stemmed trees resprouting from stumps. Q. mongolica formed the upper canopy 16–22 m tall, 88.3% of total stand basal area, and 36.2% of total stem density, with most trees established during the first post-logging decade (51.2% were resprouts). During the first three decades, the Q. mongolica recruits grew exponentially, and disproportionately more in diameter than few older reserved trees left after the last cutting. This substantially decreased size inequality. The reverse trend was observed from 1994 to 2004: larger trees grow more, indicating an increasing asymmetry of competition for light. Neighborhood analysis revealed that when target trees had more or larger neighbors, their exponential phase of growth was reduced and maximum size was decreased. After the 50 years of stand development, more than 70% of Q. mongolica showed growth decline as a result of competitive stress, and mortality was about 30%, concentrated in smaller size classes. Compared to single stems, resprouts within clones do not seem to compete less asymmetric as might be expected based on studies of clonal herbaceous plants and physiological integration within genets. As Q. mongolica was also negatively affected by competition from woody species currently prevailing in the lower tree stratum (Tilia amurensis, Acer mono, Fraxinus rhynchophylla, Acer pseudosieboldianum), we predict the stand will become increasingly dominated by these more shade-tolerant trees.