Initiation of V(D)J Recombination by Dβ-Associated Recombination Signal Sequences: A Critical Control Point in TCRβ Gene Assembly

T cell receptor (TCR) β gene assembly by V(D)J recombination proceeds via successive Dβ-to-Jβ and Vβ-to-DJβ rearrangements. This two-step process is enforced by a constraint, termed beyond (B)12/23, which prohibits direct Vβ-to-Jβ rearrangements. However the B12/23 restriction does not explain the order of TCRβ assembly for which the regulation remains an unresolved issue. The initiation of V(D)J recombination consists of the introduction of single-strand DNA nicks at recombination signal sequences (RSSs) containing a 12 base-pairs spacer. An RSS containing a 23 base-pairs spacer is then captured to form a 12/23 RSSs synapse leading to coupled DNA cleavage. Herein, we probed RSS nicks at the TCRβ locus and found that nicks were only detectable at Dβ-associated RSSs. This pattern implies that Dβ 12RSS and, unexpectedly, Dβ 23RSS initiate V(D)J recombination and capture their respective Vβ or Jβ RSS partner. Using both in vitro and in vivo assays, we further demonstrate that the Dβ1 23RSS impedes cleavage at the adjacent Dβ1 12RSS and consequently Vβ-to-Dβ1 rearrangement first requires the Dβ1 23RSS excision. Altogether, our results provide the molecular explanation to the B12/23 constraint and also uncover a ‘Dβ1 23RSS-mediated’ restriction operating beyond chromatin accessibility, which directs Dβ1 ordered rearrangements.     

Effect of vertebrate and invertebrate kairomones on the life history of Daphnia magna Straus (Crustacea: Branchiopoda)

The history of selection of Daphnia magna populations living in North African temporary ponds may differ from populations inhabiting permanent ponds. Laboratory experiments were conducted to examine the effect of fish Gambusia holbrooki and invertebrate Notonecta glauca kairomones on the life history traits of the freshwater Cladocera Daphnia magna Straus. With fish kairomones, Daphnia reproduced early and had a significantly smaller size at first reproduction (SFR) and a smaller size of neonates compared to control. In contrast, daphnids reared in water treated with Notonecta glauca had no effect on the age at first reproduction but females were also smaller and produced smaller neonates.     

Mutagenic properties of a nitrofuran, 7-methoxy-2-nitronaphtho[2,1-b]furan (R7000), in lacI transgenic mice

The in vivo mutagenic properties of a 5-nitrofuran, the 7-methoxy-2-nitronaphtho[2,1-b]furan (R7000), already well known in bacteria, was evaluated in lacI transgenic mice (Big Blue). The mutation frequency was determined in various organs of i.p. — treated mice and the nature of induced mutations was determined for the target organs in which mutation induction was significant. It was found that R7000 is mutagenic in mice, although, on the basis of the number of induced mutants per unit mass in comparison with other known mutagenic chemicals, R7000 appears to be considerably less mutagenic in mice than in bacteria. The most affected organs, small intestine, caecum and colon organs belong to the digestive apparatus. The distribution of R7000-induced mutations in the lacI gene recovered from small intestine of transgenic mice was very similar to that which had been found in E. coli. The difference between mouse and E. coli in the R7000 induced mutational spectra are mainly in the proportion of single base frameshifts versus base substitutions. Since R7000 induced mutations seemed to arise in the population of stem cells and that the stem cells are important for carcinogenesis, our results are compatible with a possible carcinogenic effect of R7000 and other nitrofurans.     

Association of laryngeal and nasopharyngeal tuberculosis: a case report

Introduction

To the best of our knowledge, the association of nasopharyngeal and laryngeal tuberculosis has never been described before in the literature. We report here a first observation.

Case presentation

We report the case of a 38-year-old Arab man who presented with an isolated hoarseness. Radiological and endoscopic examinations showed a thickening of the left lateral wall of his nasopharynx and the left vocal cord. Pathology revealed the diagnosis of tuberculosis of both localizations. He received a 6-month antituberculous chemotherapy with a satisfying uneventful evolution.

Conclusions

Tuberculosis should be considered in the differential diagnosis of soft tissue masses of the head and neck, particularly when the imaging findings and clinical presentation are atypical. The diagnosis of tuberculosis is mainly based on histopathological and/or bacteriological examination.     

Fair hop-by-hop interest rate control to mitigate congestion in named data networks

Cluster Computing - Data retrieval in Named Data Networking (NDN) is based on content names irrespective of their hosting location. The NDN architecture introduces original naming, forwarding and...     

New Intraclass Helitrons Classification Using DNA-Image Sequences and Machine Learning Approaches

Helitrons, eukaryotic transposable elements (TEs) transposed by rolling-circle mechanism, have been found in various species with highly variable copy numbers and sometimes with a large portion of their genomes. The impact of helitrons sequences in the genome is to frequently capture host genes during their transposition. Since their discovery, 18 years ago, by computational analysis of whole genome sequences of Arabidopsis thaliana plant and Caenorhabditis elegans (C. elegans) nematode, the identification and classification of these mobile genetic elements remain a challenge due to the fact that the wide majority of their families are non-autonomous. In C. elegans genome, DNA helitrons sequences possess great variability in terms of length that varies between 11 and 8965 base pairs (bps) from one sequence to another. In this work, we develop a new method to predict helitrons DNA-sequences, which is particularly based on Frequency Chaos Game Representation (FCGR) DNA-images. Thus, we introduce an automatic system in order to classify helitrons families in C. elegans genome, based on a combination between machine learning approaches and features extracted from DNA-sequences. Consequently, the new set of helitrons features (the FCGR images and K-mers) are extracted from DNA sequences. These helitrons features consist of the frequency apparition number of K nucleotides pairs (Tandem Repeat) in the DNA sequences. Indeed, three different classifiers are used for the classification of all existing helitrons families. The results have shown potential global score equal to 72.7% due to FCGR images which constitute helitrons features and the pre-trained neural network as a classifier. The two other classifiers demonstrate that their efficiency reaches 68.7% for Support Vector Machine (SVM) and 91.45% for Random Forest (RF) algorithms using the K-mers features corresponding to the genomic sequences.     

Chemical Composition of the Leaf and Flower Essential Oils of Tunisian Lavandula dentata L. (Lamiaceae)

Essential oils of Lavandula dentata, a Tunisian native plant, were isolated from leaves and flowers by hydrodistillation in a Clevenger‐type apparatus and characterized by GC‐FID and GC/MS analyses. The average essential oil yields, means of five replicates, were higher for the flowers (8.60 mg/g) than for the leaves (6.56 mg/g). A total of 72 compounds were identified, accounting for 98.1 and 97.7% of the total oil composition of the leaves and flowers, respectively. The main essential oil constituents were 1,8‐cineole, camphor, and L ‐fenchone, accounting for 33.54, 18.89, and 8.36% in the leaf oils and for 19.85, 23.33, and 7.13% in the flower oils, respectively. Besides this quantitative variation, the results also showed considerable qualitative variation between the essential oils of the two plant parts analyzed. These differences might be adaptative responses to ecological exigencies.