Élites et ordres militaires au Moyen Âge

Depuis une trentaine d'années, l'étude des ordres militaires au Moyen Âge a enregistré un profond renouvellement auquel Alain Demurger a particulièrement œuvré. Derrière l'histoire politique, par-delà les rouages institutionnels, la recherche s'est toujours plus attachée à considérer les hommes. Pourtant, la question des élites, s'agissant des frères, n'a jamais été analysée sinon de façon ponctuelle. En considérant à la fois les élites sociales, nobles ou citadines, les élites de pouvoir et de gouvernement et les propres élites des ordres militaires, ce livre n'apporte pas seulement un nouvel éclairage sur l'histoire des frères. Il contribue plus largement à la connaissance des sociétés médiévales, du xiie au xve siècle, depuis la péninsule Ibérique jusqu'à la Baltique et à l'Orient méditerranéen

Evolution of the bile salt nuclear receptor FXR in vertebrates*s⃞

Bile salts, the major end metabolites of cholesterol, vary significantly in structure across vertebrate species, suggesting that nuclear receptors binding these molecules may show adaptive evolutionary changes. We compared across species the bile salt specificity of the major transcriptional regulator of bile salt synthesis, the farnesoid X receptor (FXR). We found that FXRs have changed specificity for primary bile salts across species by altering the shape and size of the ligand binding pocket. In particular, the ligand binding pockets of sea lamprey (Petromyzon marinus) and zebrafish (Danio rerio) FXRs, as predicted by homology models, are flat and ideal for binding planar, evolutionarily early bile alcohols. In contrast, human FXR has a curved binding pocket best suited for the bent steroid ring configuration typical of evolutionarily more recent bile acids. We also found that the putative FXR from the sea squirt Ciona intestinalis, a chordate invertebrate, was completely insensitive to activation by bile salts but was activated by sulfated pregnane steroids, suggesting that the endogenous ligands of this receptor may be steroidal in nature. Our observations present an integrated picture of the coevolution of bile salt structure and of the binding pocket of their target nuclear receptor FXR

Toward a Phylogenetic Reconstruction of Organizational Life

cladistics, classification, configurations, diversity, evolution, organizations, phylogeny, taxonomy, typology, A1, L0, L2, L6, M1, N0,