11 research outputs found
Monoallelic expression and epigenetic memory sustained by a Trypanosoma brucei variant surface glycoprotein exclusion complex
The dipole-modifying effect of styrylpyridinium dyes and flavonoids on model membranes of different lipid compositions
Steric exclusion and protein conformation determine the localization of plasma membrane transporters
Spatial integration of transcription and splicing in a dedicated compartment sustains monogenic antigen expression in African trypanosomes
Highly selective gene expression is a key requirement for antigenic variation in several pathogens, allowing evasion of host immune responses and maintenance of persistent infections (1). African trypanosomes, parasites that cause lethal diseases in humans and livestock, employ an antigenic variation mechanism that involves monogenic antigen expression from a pool of >2600 antigen-coding genes (2). In other eukaryotes, the expression of individual genes can be enhanced by mechanisms involving the juxtaposition of otherwise distal chromosomal loci in the three-dimensional nuclear space (3â5). However, trypanosomes lack classical enhancer sequences or regulated transcription initiation (6,7). In this context, it has remained unclear how genome architecture contributes to monogenic transcription elongation and transcript processing. Here, we show that the single expressed antigen coding gene displays a specific inter-chromosomal interaction with a major mRNA splicing locus. Chromosome conformation capture (Hi-C) revealed a dynamic reconfiguration of this inter-chromosomal interaction upon activation of another antigen. Super-resolution microscopy showed the interaction to be heritable and splicing dependent. We find a specific association of the two genomic loci with the antigen exclusion complex, whereby VEX1 occupied the splicing locus and VEX2 the antigen coding locus. Following VEX2 depletion, loss of monogenic antigen expression was accompanied by increased interactions between previously silent antigen genes and the splicing locus. Our results reveal a mechanism to ensure monogenic expression, where antigen transcription and mRNA splicing occur in a specific nuclear compartment. These findings suggest a new means of post-transcriptional gene regulation
Changes in Membrane Organization upon Spontaneous Insertion of 2-Hydroxylated Unsaturated Fatty Acids in the Lipid Bilayer
Recent research regarding 2-hydroxylated fatty acids (2OHFAs) showed clear evidence of their benefits in the treatment of cancer, inflammation, and neurodegenerative disorders such as Alzheimerâs disease. Monolayer compressibility isotherms and isothermal titration calorimetry of 2OHFA (C18âC22) in phosphatidylcholine/phosphatidylethanolamine/sphingomyelin/cholesterol (1:1:1:1 mole ratio), a
mixture that mimics the composition of mammalian plasma membrane, were performed to assess the membrane binding capacity of 2OHFAs and their natural, nonhydroxylated counterparts. The results show that 2OHFAs are surfaceactive substances that bind membranes through exothermic, spontaneous processes. The main effects of 2OHFAs are a decrease in lipid order, with a looser packing of the acyl chains, and a decreased dipole potential, regardless of the 2OHFAsâ relative affinity for the lipid bilayer. The strongest effects are usually observed for 2-hydroxyarachidonic (C20:4) acid, and the weakest one, for 2-hydroxydocosahexaenoic acid (C22:6). In addition, 2OHFAs cause increased hydration, except in gel-phase membranes, which can be explained by the 2OHFA preference for membrane defects. Concerning the membrane dipole potential, the magnitude of the reduction induced by 2OHFAs was particularly marked in the liquid-ordered (lo) phase (cholesterol/sphingomyelin-rich) membranes, those where order reduction was the smallest, suggesting a disruption of cholesterolâsphingolipid interactions that are responsible for the large dipole potential in those membranes. Moreover, 2OHFA effects were larger than for both lo and ld phases separately in model
membranes with liquid disordered (ld)/lo coexistence when both phases were present in significant amounts, possibly because of the facilitating effect of ld/lo domain interfaces. The specific and marked changes induced by 2OHFAs in several membrane properties suggest that the initial interaction with the membrane and subsequent reorganization might constitute an important step in their mechanisms of action.Ministerio de EconomĂa y Competitividad (Torres-Quevedo Research Contracts, PTQ-10-04214 and PTQ-09-02-02113).
FundacioÌn Marathon
Grants to Research Groups of Excellence from Govern de les Illes Balears
Basque Government (IT849-13)
Spanish Ministerio de Ciencia e InnovacioÌn (BFU2012-36241, BIO2010-21132)
Portuguese national funds and Fundo Social Europeu through FCT, the Portuguese Foundation for Science and Technology, by âCieÌncia 2007âand âInvestigador FCT 2012â Initiatives (POPH), and by grant PEst-OE/QUI/UI0612/2011-2013.
FundaçaÌo Amadeu Dias/Universidade de Lisboa