A search for reverse transcriptase-coding sequences reveals new non-LTR retrotransposons in the genome of Drosophila melanogaster

BACKGROUND: Non-long terminal repeat (non-LTR) retrotransposons are eukaryotic mobile genetic elements that transpose by reverse transcription of an RNA intermediate. We have performed a systematic search for sequences matching the characteristic reverse transcriptase domain of non-LTR retrotransposons in the sequenced regions of the Drosophila melanogaster genome. RESULTS: In addition to previously characterized BS, Doc, F, G, I and Jockey elements, we have identified new non-LTR retrotransposons: Waldo, You and JuanDm. Waldo elements are related to mosquito RTI elements. You to the Drosophila I factor, and JuanDm to mosquito Juan-A and Juan-C. Interestingly, all JuanDm elements are highly homogeneous in sequence, suggesting that they are recent components of the Drosophila genome. CONCLUSIONS: The genome of D. melanogaster contains at least ten families of non-site-specific non-LTR retrotransposons representing three distinct clades. Many of these families contain potentially active members. Fine evolutionary analyses must await the more accurate sequences that are expected in the next future

Le journal de bord en formation : une parole de travail

L'article étudie le rôle d'une écriture quotidienne sur la pratique des stagiaires PE2 pendant le stage en responsabilité. Il met en évidence l'émergence d'un certain nombre de « postures d'enseignement » qui très tôt différencient les stagiaires. Il met aussi en évidence comment diverses strates d'écriture, permettant un retour réflexif sur la pratique accompagnent la construction d'une identité professionnelle singulière.This article studies the role plan, ed by daily written logbook entries upon the professional practice of elementary school student teachers during the "stage en responsabilité" internship period held in their second year of training. It reveals the emergence of a certain number of "teaching attitudes/standpoints" which very quickly set the trainees apart from each other. It also reveals how various levels of writing, from simple notes to well thought out texts, by allowing the trainees to reflect on their professional practice, help them build their individual professional identity

Les pratiques langagières des enseignants : des savoirs professionnels inédits en formation

International audienceDans les IUFM nous formons de futurs professionnels de l'enseignement, métier dans lequel la parole est un instrument de travail essentiel, le médiateur principal des interactions maître/élèves lors des apprentissages des élèves. Savons nous préparer les enseignants à ces conduites langagières de la classe ? Savons-nous repérer et analyser l'impact des gestes langagiers et corporels dans la construction des apprentissages ? L'article fait état d'une recherche en cours sur cette question. Il propose une théorisation de la parole de l'enseignant dans la classe et montre quelques problèmes qu'elle soulève chez les stagiaires dans le moment particulier et précisément étudié des débuts de cours. Dans le cadre de cet article, il s'agit d'un début de cours en mathématiques

In vivo RNA localization of I factor, a non-LTR retrotransposon, requires a cis-acting signal in ORF2 and ORF1 protein

According to the current model of non-LTR retrotransposon (NLR) mobilization, co-expression of the RNA transposition intermediate, and the proteins it encodes (ORF1p and ORF2p), is a requisite for the formation of cytoplasmic ribonucleoprotein complexes which contain necessary elements to complete a retrotransposition cycle later in the nucleus. To understand these early processes of NLR mobilization, here we analyzed in vivo the protein and RNA expression patterns of the I factor, a model NLR in Drosophila. We show that ORF1p and I factor RNA, specifically produced during transposition, are co-expressed and tightly co-localize with a specific pattern (Loc+) exclusively in the cytoplasm of germ cells permissive for retrotransposition. Using an ORF2 mutated I factor, we show that ORF2p plays no role in the Loc+ patterning. With deletion derivatives of an I factor we define an RNA localization signal required to display the Loc+ pattern. Finally, by complementation experiments we show that ORF1p is necessary for the efficient localization of I factor RNA. Our data suggest that ORF1p is involved in proper folding and stabilization of I factor RNA for efficient targeting, through Loc+ patterning, to the nuclear neighborhood where downstream steps of the retrotransposition process occur

Characterization of a nucleocapsid-like region and of two distinct primer tRNA(Lys,2) binding sites in the endogenous retrovirus Gypsy

Mobile LTR-retroelements comprising retroviruses and LTR-retrotransposons form a large part of eukaryotic genomes. Their mode of replication and abundance favour the notion that they are major actors in eukaryote evolution. The Gypsy retroelement can spread in the germ line of the fruit fly Drosophila melanogaster via both env-independent and env-dependent processes. Thus, Gypsy is both an active retrotransposon and an infectious retrovirus resembling the gammaretrovirus MuLV. However, unlike gammaretroviruses, the Gypsy Gag structural precursor is not processed into Matrix, Capsid and Nucleocapsid (NC) proteins. In contrast, it has features in common with Gag of the ancient yeast TY1 retroelement. These characteristics of Gypsy make it a very interesting model to study replication of a retroelement at the frontier between ancient retrotransposons and retroviruses. We investigated Gypsy replication using an in vitro model system and transfection of insect cells. Results show that an unstructured domain of Gypsy Gag has all the properties of a retroviral NC. This NC-like peptide forms ribonucleoparticle-like complexes upon binding Gypsy RNA and directs the annealing of primer tRNA(Lys,2) to two distinct primer binding sites (PBS) at the genome 5′ and 3′ ends. Only the 5′ PBS is indispensable for cDNA synthesis in vitro and in Drosophila cells