Stimulation by thyrotropin of horse thyroid plasma membranes adenylate cyclase: evidence of cooperativity

Horse thyroid plasma membranes were prepared by partition in an aqueous two phases system. The membrane fraction was enriched in adenylate cyclase and only slightly contaminated with mitochondria and lysosomes. Adenylate cyclase activity was stimulated by TSH and PGE₁. The TSH stimulatory effect was nearly immediate and occured in the same range of concentrations that activates intact cell metabolism. It was potentiated by GTP and ITP. A quantitative analysis of the data suggests that activation of thyroid adenylate cyclase by TSH is a cooperative process.     

A study of a Man-made freshwater reservoir in Eastern Flanders (Belgium), with special reference to the vertical migration of the zooplankton

Summary A study is made of the vertical migrations of several zooplankters in a recent artificial freshwater reservoir in the lower part of Belgium. Two series of cyclical observations were made, the first one during summer stagnation (30 hours), the second one during autumn overturn (48 hours).In both cases numerous plankton collections were made at different depths and a number of physico-chemical features of the water, suspected to show a diurnal rhythm too, were determined (temperature, O₂, pH, HCO _inf3 ^sup– ).Using the statistical technique basically developed by Ricker, significant vertical migrations were found during the stratification period and for every species that was taken into consideration.During overturn, vertical migrations were much less evident and in some cases even doubtful.The causality of this phenomenon is briefly discussed.

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Résumé Les migrations verticales de plusieurs espèces d'animaux planctoniques dans un bassin d'eau douce artificiel en basse Belgique font l'objet de cette étude.Deux séries d'observations ont été effectuées, dont la première pendant la période de stratification estivale (30 heures d'observations) et la seconde au cours de la circulation automnale (48 heures d'observations).De nombreuses pèches ont été faites (toutes les trois heures ou toutes les heures et demie), à diverses profondeurs.Simultanément, un nombre de facteurs physico-chimiques, présentant eux aussi un rhythme journalier, ont été déterminés (pH, HCO _inf3 ^sup– , O₂, températures).La démonstration des migrations verticales s'est faite à l'aide des techniques de statistique développées essentiellement par Ricker.Des migrations verticales trés prononcées se sont produites pendant la période de stratification. Par contre, pendant l'overturn la structure verticale du plankton était plutôt homogène et les migrations verticales avaient perdu beaucoup de leur netteté. Dans certains cas elles sont peut-être absentes ou camouflées par des mouvements horizontaux.La causalité de cette différence marquante entre les deux périodes de l'année fait l'objet d'une brève discussion.

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Asvirant F.N.R.S.-N.F.W.O., België.     

Correlation of bistranded clustered abasic DNA lesion processing with structural and dynamic DNA helix distortion

Clustered apurinic/apyrimidinic (AP; abasic) DNA lesions produced by ionizing radiation are by far more cytotoxic than isolated AP lesion entities. The structure and dynamics of a series of seven 23-bp oligonucleotides featuring simple bistranded clustered damage sites, comprising of two AP sites, zero, one, three or five bases 3′ or 5′ apart from each other, were investigated through 400 ns explicit solvent molecular dynamics simulations. They provide representative structures of synthetically engineered multiply damage sites-containing oligonucleotides whose repair was investigated experimentally (Nucl. Acids Res. 2004, 32:5609-5620; Nucl. Acids Res. 2002, 30: 2800–2808). The inspection of extrahelical positioning of the AP sites, bulge and non Watson–Crick hydrogen bonding corroborates the experimental measurements of repair efficiencies by bacterial or human AP endonucleases Nfo and APE1, respectively. This study provides unprecedented knowledge into the structure and dynamics of clustered abasic DNA lesions, notably rationalizing the non-symmetry with respect to 3′ to 5′ position. In addition, it provides strong mechanistic insights and basis for future studies on the effects of clustered DNA damage on the recognition and processing of these lesions by bacterial or human DNA repair enzymes specialized in the processing of such lesions.     

Role of extracellular charged amino acids in the yeast alpha-factor receptor

The yeast pheromone receptor, Ste2p, is a G protein coupled receptor that initiates cellular responses to alpha-mating pheromone, a 13 residue peptide that carries a net positive charge at physiological pH. We have examined the role of extracellular charged groups on the receptor in response to the pheromone. Substitutions of Asn or Ala for one extracellular residue, Asp275, affected both pheromone binding and signaling, suggesting that this position interacts directly with ligand. The other seven extracellular acidic residues could be individually replaced by polar residues with no detectable effects on receptor function. However, substitution of Ala for each of these seven residues resulted in impairment of signaling without affecting pheromone binding, implying that the polar nature of these residues promotes receptor activation. In contrast, substitution of Ala for each of the six positively charged residues at the extracellular surface of Ste2p did not affect signaling.     

Identification of an MHC class I-restricted autoantigen in type 1 diabetes by screening an organ-specific cDNA library.

Type 1 diabetes is an autoimmune disease in which the insulin-producing pancreatic beta cells are destroyed at an early age by an immune process that involves both CD4 and CD8 T lymphocytes. The identification of autoantigens in diabetes is very important for the design of antigen-specific immunotherapy. By screening a pancreatic islet cDNA library, we have identified the autoantigen recognized by highly pathogenic CD8 T cells in the non-obese diabetic mouse, one of the best animal models for human diabetes. This is the first identification, to our knowledge, of a CD8 T-cell epitope in an autoimmune disease. The peptide recognized by the cells is in the same region of the insulin B chain as the epitope recognized by previously isolated pathogenic CD4 T cells. This has very important implications for the potential use of insulin in preventative therapy.     

Wake up of transposable elements following Drosophila simulans worldwide colonization.

Transposable elements (TEs) make up around 10%-15% of the Drosophila melanogaster genome, but its sibling species Drosophila simulans carries only one third as many such repeat sequences. We do not, however, have an overall view of copy numbers of the various classes of TEs (long terminal repeat [LTR] retrotransposons, non-LTR retrotransposons, and transposons) in genomes of natural populations of both species. We analyzed 34 elements in individuals from various natural populations of these species. We show that D. melanogaster has higher average chromosomal insertion site numbers per genome than D. simulans for all TEs except five. The LTR retrotransposons gypsy, ZAM, and 1731 and the transposon bari-1 present similar low copy numbers in both species. The transposon hobo has a large number of insertion sites, with significantly more sites in D. simulans. High variation between populations in number of insertion sites of some elements of D. simulans suggests that these elements can invade the genome of the entire species starting from a local population. We propose that TEs in the D. simulans genome are being awakened and amplified as they had been a long time ago in D. melanogaster.     

Fibro-adipogenic progenitors in skeletal muscle homeostasis,regeneration and diseases

Skeletal muscle possesses a remarkable regenerative capacity that relies on the activity of muscle stem cells, also known as satellite cells. The presence of non-myogenic cells also plays a key role in the coordination of skeletal muscle regeneration. Particularly, fibro-adipogenic progenitors (FAPs) emerged as master regulators of muscle stem cell function and skeletal muscle regeneration. This population of muscle resident mesenchymal stromal cells has been initially characterized based on its bi-potent ability to differentiate into fibroblasts or adipocytes. New technologies such as single-cell RNAseq revealed the cellular heterogeneity of FAPs and their complex regulatory network during muscle regeneration. In acute injury, FAPs rapidly enter the cell cycle and secrete trophic factors that support the myogenic activity of muscle stem cells. Conversely, deregulation of FAP cell activity is associated with the accumulation of fibrofatty tissue in pathological conditions such as muscular dystrophies and ageing. Considering their central role in skeletal muscle pathophysiology, the regulatory mechanisms of FAPs and their cellular and molecular crosstalk with muscle stem cells are highly investigated in the field. In this review, we summarize the current knowledge on FAP cell characteristics, heterogeneity and the cellular crosstalk during skeletal muscle homeostasis and regeneration. We further describe their role in muscular disorders, as well as different therapeutic strategies targeting these cells to restore muscle regeneration.