Key physiological parameters dictate triggering of activity-dependent bulk endocytosis in hippocampal synapses

To maintain neurotransmission in central neurons, several mechanisms are employed to retrieve synaptically exocytosed membrane. The two major modes of synaptic vesicle (SV) retrieval are clathrin-mediated endocytosis and activity-dependent bulk endocytosis (ADBE). ADBE is the dominant SV retrieval mode during intense stimulation, however the precise physiological conditions that trigger this mode are not resolved. To determine these parameters we manipulated rat hippocampal neurons using a wide spectrum of stimuli by varying both the pattern and duration of stimulation. Using live-cell fluorescence imaging and electron microscopy approaches, we established that stimulation frequency, rather than the stimulation load, was critical in the triggering of ADBE. Thus two hundred action potentials, when delivered at high frequency, were sufficient to induce near maximal bulk formation. Furthermore we observed a strong correlation between SV pool size and ability to perform ADBE. We also identified that inhibitory nerve terminals were more likely to utilize ADBE and had a larger SV recycling pool. Thus ADBE in hippocampal synaptic terminals is tightly coupled to stimulation frequency and is more likely to occur in terminals with large SV pools. These results implicate ADBE as a key modulator of both hippocampal neurotransmission and plasticity.     

The mutational dynamics of the SARS-CoV-2 virus in serial passages in vitro

Since its outbreak in 2019, Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) keeps surprising the medical community by evolving diverse immune escape mutations in a rapid and effective manner. To gain deeper insight into mutation frequency and dynamics, we isolated ten ancestral strains of SARS-CoV-2 and performed consecutive serial incubation in ten replications in a suitable and common cell line and subsequently analysed them using RT-qPCR and whole genome sequencing. Along those lines we hoped to gain fundamental insights into the evolutionary capacity of SARS-CoV-2 in vitro. Our results identified a series of adaptive genetic changes, ranging from unique convergent substitutional mutations and hitherto undescribed insertions. The region coding for spike proved to be a mutational hotspot, evolving a number of mutational changes including the already known substitutions at positions S:484 and S:501. We discussed the evolution of all specific adaptations as well as possible reasons for the seemingly inhomogeneous potential of SARS-CoV-2 in the adaptation to cell culture. The combination of serial passage in vitro with whole genome sequencing uncovers the immense mutational potential of some SARS-CoV-2 strains. The observed genetic changes of SARS-CoV-2 in vitro could not be explained solely by selectively neutral mutations but possibly resulted from the action of directional selection accumulating favourable genetic changes in the evolving variants, along the path of increasing potency of the strain. Competition among a high number of quasi-species in the SARS-CoV-2 in vitro population gene pool may reinforce directional selection and boost the speed of evolutionary change.     

Revisiting santa rosalia to unfold a degeneracy of classic models of speciation

Abstract Many classic models of speciation incorporate assortative mating based on mating groups, such as plants with different flowering times, and they investigate whether an ecological trait under disruptive natural selection becomes genetically associated with the selectively neutral mating trait. It is well known that this genetic association is potently destroyed by recombination. In this note, we point out a more fundamental difficulty: if a "knife-edge" symmetry assumption of previous models is violated, then the mating trait is no longer neutral and sexual selection eliminates the polymorphism in the mating locus. This result strengthens the growing consensus that magic traits are the more likely route to nonallopatric speciation. We expand the model assuming also ecological selection on the mating trait and investigate the conditions for natural selection to overcome sexual selection and maintain mating polymorphism; we find that the combination of natural and sexual selection can cause also bistability of allele frequencies.     

Transmission of genome damage from irradiated male rats to their progeny

The effect of gamma-radiation (3Gy) on slowly proliferating liver tissue of male rats and their progeny was investigated with respect to induction and duration of latent damage. The irradiation caused latent cytogenetic damage in the liver in irradiated males of the F(0) generation, which manifested itself in different ways during proliferation of hepatocytes induced by partial hepatectomy: a reduced proliferating activity, a higher frequency of chromosomal aberrations and a higher proportion of cells with apoptotic DNA fragments were observed, compared with non-irradiated rats. In the progeny of irradiated males (F(1) and F(2) generation), the latent genome damage manifested itself during regeneration of the liver after partial hepatectomy by similar, but less pronounced changes compared with those seen in irradiated males of the parental generation. This finding gave evidence of the transfer of part of the radiation-induced genome damage from parents to their offspring. Irradiation of F(1) and F(2) progeny of irradiated males (their total radiation load being 3 + 3 and 3 + 0 + 3 Gy, respectively) caused less change as irradiation of progeny of non-irradiated control males (their total radiation load being 0 + 3 and 0 + 0 + 3 Gy, respectively).     

Changes in the biological activity of agropyrene on combined application with humus substances in the cultivation ofScenedesmus obliquus (TURP.) krüger

The work is concerned with the question of the effect of humic acids on the biological action of agropyrene, the effective substance from the rootstock of Agropyron repens (L.) P. BEAUV. The test organism was the alga Scenedesmus obliquus (TURP.) KRÜGER, cultivated in mineral solution. The basic biological test was the determination of the number and size of the cells of this alga. It was found that the way in which agropyrene acts on combined application with humus acids depends on which humus fraction is used. It can display a synergic action if humic acid is used, since this substance probably facilitates the penetration of agropyrene into the cells. On the other hand, fulvic acid counteracts the activity of agropyrene and this most probably by mutual binding and blocking of active groups and links.     

Exercise-induced lipid mobilization in subcutaneous adipose tissue is mainly related to natriuretic peptides in overweight men

Involvement of sympathetic nervous system and natriuretic peptides in the control of exercise-induced lipid mobilization was compared in overweight and lean men. Lipid mobilization was determined using local microdialysis during exercise. Subjects performed 35-min exercise bouts at 60% of their maximal oxygen consumption under placebo or after oral tertatolol [a beta-adrenergic receptor (AR) antagonist]. Under placebo, exercise increased dialysate glycerol concentration (DGC) in both groups. Phentolamine (alpha-AR antagonist) potentiated exercise-induced lipolysis in overweight but not in lean subjects; the alpha(2)-antilipolytic effect was only functional in overweight men. After tertatolol administration, the DGC increased similarly during exercise no matter which was used probe in both groups. Compared with the control probe under placebo, lipolysis was reduced in lean but not in overweight men treated with the beta-AR blocker. Tertatolol reduced plasma nonesterified fatty acids and insulin concentration in both groups at rest. Under placebo or tertatolol, the exercise-induced changes in plasma nonesterified fatty acids, glycerol, and insulin concentrations were similar in both groups. Exercise promoted a higher increase in catecholamine and ANP plasma levels after tertatolol administration. In conclusion, the major finding of our study is that in overweight men, in addition to an increased alpha(2)-antilipolytic effect, the lipid mobilization in subcutaneous adipose tissue that persists during exercise under beta-blockade is not dependent on catecholamine action. On the basis of correlation findings, it seems to be related to a concomitant exercise-induced rise in plasma ANP when exercise is performed under tertatolol intake and a decrease in plasma insulin.     

Chromocentre integrity and epigenetic marks

The epigenetic modification of histones dictates the formation of euchromatin and heterochromatin domains. We studied the effects of a deficiency of histone methyltransferase, SUV39h, and trichostatin A-dependent hyperacetylation on the structural stability of centromeric clusters, called chromocentres. We did not observe the expected disintegration of chromocentres, but both SUV39h deficiency and hyperacetylation in SUV39h+/+ cells induced the re-positioning of chromocentres closer to the nuclear periphery. Conversely, TSA treatment of SUV39h?/? cells re-established normal nuclear radial positioning of chromocentres. This structural re-arrangement was likely caused by several epigenetic events at centromeric heterochromatin. In particular, reciprocal exchanges between H3K9me1, H3K9me2, H3K9me3, DNA methylation, and HP1 protein levels influenced chromocentre nuclear composition. For example, H3K9me1 likely substituted for the function of H3K9me3 in chromocentre nuclear arrangement and compaction. Our results illustrate the important and interchangeable roles of epigenetic marks for chromocentre integrity. Therefore, we propose a model for epigenetic regulation of nuclear stability of centromeric heterochromatin in the mouse genome.