tRNASec is transcribed by RNA polymerase II in Trypanosoma brucei but not in humans

Nuclear-encoded tRNAs are universally transcribed by RNA polymerase III (Pol-III) and contain intragenic promoters. Transcription of vertebrate tRNASec however requires extragenic promoters similar to Pol-III transcribed U6 snRNA. Here, we present a comparative analysis of tRNASec transcription in humans and the parasitic protozoa Trypanosoma brucei, two evolutionary highly diverged eukaryotes. RNAi-mediated ablation of Pol-II and Pol-III as well as oligo-dT induced transcription termination show that the human tRNASec is a Pol-III transcript. In T. brucei protein-coding genes are polycistronically transcribed by Pol-II and processed by trans-splicing and polyadenylation. tRNA genes are generally clustered in between polycistrons. However, the trypanosomal tRNASec genes are embedded within a polycistron. Their transcription is sensitive to α-amanitin and RNAi-mediated ablation of Pol-II, but not of Pol-III. Ectopic expression of the tRNASec outside but not inside a polycistron requires an added external promoter. These experiments demonstrate that trypanosomal tRNASec, in contrast to its human counterpart, is transcribed by Pol-II. Synteny analysis shows that in trypanosomatids the tRNASec gene can be found in two different polycistrons, suggesting that it has evolved twice independently. Moreover, intron-encoded tRNAs are present in a number of eukaryotic genomes indicating that Pol-II transcription of tRNAs may not be restricted to trypanosomatid

A quantitative telomeric chromatin isolation protocol identifies different telomeric states

Telomere composition changes during tumourigenesis, aging and in telomere syndromes in a poorly defined manner. Here we develop a quantitative telomeric chromatin isolation protocol (QTIP) for human cells, in which chromatin is cross-linked, immunopurified and analysed by mass spectrometry. QTIP involves stable isotope labelling by amino acids in cell culture (SILAC) to compare and identify quantitative differences in telomere protein composition of cells from various states. With QTIP, we specifically enrich telomeric DNA and all shelterin components. We validate the method characterizing changes at dysfunctional telomeres, and identify and validate known, as well as novel telomere-associated polypeptides including all THO subunits, SMCHD1 and LRIF1. We apply QTIP to long and short telomeres and detect increased density of SMCHD1 and LRIF1 and increased association of the shelterins TRF1, TIN2, TPP1 and POT1 with long telomeres. Our results validate QTIP to study telomeric states during normal development and in diseas

tRNASec is transcribed by RNA polymerase II in Trypanosoma brucei but not in humans

Nuclear-encoded tRNAs are universally transcribed by RNA polymerase III (Pol-III) and contain intragenic promoters. Transcription of vertebrate tRNASec however requires extragenic promoters similar to Pol-III transcribed U6 snRNA. Here, we present a comparative analysis of tRNASec transcription in humans and the parasitic protozoa Trypanosoma brucei, two evolutionary highly diverged eukaryotes. RNAi-mediated ablation of Pol-II and Pol-III as well as oligo-dT induced transcription termination show that the human tRNASec is a Pol-III transcript. In T. brucei protein-coding genes are polycistronically transcribed by Pol-II and processed by trans-splicing and polyadenylation. tRNA genes are generally clustered in between polycistrons. However, the trypanosomal tRNASec genes are embedded within a polycistron. Their transcription is sensitive to α-amanitin and RNAi-mediated ablation of Pol-II, but not of Pol-III. Ectopic expression of the tRNASec outside but not inside a polycistron requires an added external promoter. These experiments demonstrate that trypanosomal tRNASec, in contrast to its human counterpart, is transcribed by Pol-II. Synteny analysis shows that in trypanosomatids the tRNASec gene can be found in two different polycistrons, suggesting that it has evolved twice independently. Moreover, intron-encoded tRNAs are present in a number of eukaryotic genomes indicating that Pol-II transcription of tRNAs may not be restricted to trypanosomatids

ALT Telomeres Get Together with Nuclear Receptors

Nuclear receptors bind chromosome ends in "alternative lengthening of telomeres" (ALT) cancer cells that maintain their ends by homologous recombination instead of telomerase. Marzec et al. now demonstrate that, in ALT cells, nuclear receptors not only trigger distal chromatin associations to mediate telomere-telomere recombination events, but also drive chromosome-internal targeted telomere insertions (TTI)

Collecting data on family configuration

Contemporary family contexts are characterized by a complex web of relationships, which goes beyond the household boundaries. Indeed, individuals develop meaningful relationships with non-residential family members, close friends, neighbors, colleagues, etc. Unfortunately, most surveys dealing with family ties focus on households and study a few dyads, mainly couple and parent–child relationships. This contribution addresses the use of social network methods for the understanding of the social matrix of family interdependencies in which individuals are embedded. Social network methods broaden the definition of family by starting with the individuals' own definition of their meaningful family context. They also allow the mapping of family networks based on the interdependencies existing among all family members. This contribution describes the use of social network methods in relation to three main settings: individuals in national representative surveys, individuals facing a family recomposition after divorce, and individuals in psychotherapy. In the light of the pluralization of life trajectories and the individualization of personal relationships, the proposed approach may significantly contribute to the understanding of the relationships that matter for individuals in contemporary societies, and of the creation of family-based social capital

Les recompositions familiales dans une perspective configurationnelle

L'émergence de nouvelles formes familiales suscite des questionnements. Assiste-t-on à un déclin décisif de la famille comme institution dans les sociétés occidentales et, en particulier, à un affaiblissement de sa fonction d'intégration sociale ? La diminution en nombre des familles nucléaires, constituées d'un couple reconnu socialement et de ses enfants biologiques cohabitant, rattrapées par le vieillissement de la population (qui multiplie les ménages d'une seule personne) et par la pluralisation des parcours de vie, pose question. Le problème se pose tout particulièrement dans le cas de recompositions familiales après une séparation et une remise en couple, transitions qui provoquent une multiplication des rôles familiaux. Comment définir les frontières d'une famille recomposée ? Comment la relation parentale, et la nouvelle relation conjugale qui s'instaure coexistent-elles dans ces contextes ? Cette contribution entend amener quelques éléments de réponse à ces importantes questions en privilégiant une approche configurationnelle des familles recomposées

Recomposition familiale: variété des configurations et ancrage sociodémographique

L'étude des recompositions familiales met en exergue les limites des approches de la famille basées sur les unités d'analyse du ménage et de la corésidence. Les analyses présentées dans cet article ont été menées à partir d'une enquête quantitative qui adopte une approche configurationnelle des familles. Elles se focalisent sur les interdépendances relationnelles entre les individus définis comme membres significatifs de leur famille par les répondants. A partir des liens familiaux de 300 femmes, neuf types de configurations familiales ont été dégagées. Les résultats montrent que ces configurations familiales dépassent pour la plupart le cadre du ménage. Ils démontrent que la dichotomie entre famille de première union et famille recomposée est réductrice et peut être empiriquement dépassée. Finalement, confrontées aux limites imposées par le réservoir de parenté et la spatialité, les configurations familiales se présentent comme étant à la fois ancrées dans un contexte sociodémographique contraignant et générées par les choix de vie des individus qui les composent

Beyond the nuclear family: Personal networks in light of work-family trajectories

Individuals develop personal networks in a cumulative way over the life course, with early adulthood being a critical period with multiple transitions relating to family formation and entry into the labour market. Existing research on personal networks and the life course usually stresses the impact of single life transitions and events on the composition of personal networks. Contrastingly, this paper investigates the impact of whole work-family trajectories over a retrospective time period of 20 years corresponding to early adulthood (roughly 20 to 40 years old) on the composition of personal networks. Drawing on a Swiss sample of individuals born between 1970 and 1975, results revealed the critical impact of the family trajectories for the development of personal networks, and showed how the current diversity of personal networks is accounted for by trajectories deviating from the family developmental model