Capping and alpha-helix stability

The first and last four residues of alpha-helices differ from the rest by not being able to make the intrehelical hydrogen bonds between the backbone greater than C=O groups of one turn and the greater than NH groups of the next. Physico-chemical arguments and statistical analysis suggest that there is a preference for certain residues at the C and N termini (The C- and N-caps) that can fulfil the hydrogen bonding requirements. We have tested this hypothesis by constructing a series of mutations in the two N-caps of barnase (Bacillus amyloliquefaciens ribonuclease, positions Thr 6 and Thr 26) and determining the change in their stability. The N-cap is found to stabilize the protein by up to approximately 2.5 kcal mol(-1). The presence of a negative charge of the N-cap adds some 1.6 kcal mol(-1) of stabilization energy because of the interaction with the macroscopic electrostatic dipole of the helix.     

Scarites buparius,a caraboid beetle with an X1X2Y sex-chromosomes system

Summary Scarites buparius has 2n=37 and n=17+X₁X₂Y. This multiple sex-chromosomes system seems to be the result of a reciprocal translocation between the primitive X-chromosome and an autosome. This is the first caraboid beetle, exceptingCicindela spp., that has multiple sex-chromosomes.This work has been supported by a grant of the Comisión Asesora de Investigación Científica y Técnica, No. 1.552.     

Global trends of whole-genome duplications revealed by the ciliate Paramecium tetraurelia

The duplication of entire genomes has long been recognized as having great potential for evolutionary novelties, but the mechanisms underlying their resolution through gene loss are poorly understood. Here we show that in the unicellular eukaryote Paramecium tetraurelia, a ciliate, most of the nearly 40,000 genes arose through at least three successive whole-genome duplications. Phylogenetic analysis indicates that the most recent duplication coincides with an explosion of speciation events that gave rise to the P. aurelia complex of 15 sibling species. We observed that gene loss occurs over a long timescale, not as an initial massive event. Genes from the same metabolic pathway or protein complex have common patterns of gene loss, and highly expressed genes are over-retained after all duplications. The conclusion of this analysis is that many genes are maintained after whole-genome duplication not because of functional innovation but because of gene dosage constraints.     

From in vivo to in silico biology and back

The massive acquisition of data in molecular and cellular biology has led to the renaissance of an old topic: simulations of biological systems. Simulations, increasingly paired with experiments, are being successfully and routinely used by computational biologists to understand and predict the quantitative behaviour of complex systems, and to drive new experiments. Nevertheless, many experimentalists still consider simulations an esoteric discipline only for initiates. Suspicion towards simulations should dissipate as the limitations and advantages of their application are better appreciated, opening the door to their permanent adoption in everyday research.     

Conserved regulation of proximodistal limb axis development by Meis1/Hth

Vertebrate limbs grow out from the flanks of embryos, with their main axis extending proximodistally from the trunk. Distinct limb domains, each with specific traits, are generated in a proximal-to-distal sequence during development. Diffusible factors expressed from signalling centres promote the outgrowth of limbs and specify their dorsoventral and anteroposterior axes. However, the molecular mechanism by which limb cells acquire their proximodistal (P-D) identity is unknown. Here we describe the role of the homeobox genes Meis1/2 and Pbx1 in the development of mouse, chicken and Drosophila limbs. We find that Meis1/2 expression is restricted to a proximal domain, coincident with the previously reported domain in which Pbx1 is localized to the nucleus, and resembling the distribution of the Drosophila homologues homothorax (hth) and extradenticle (exd); that Meis1 regulates Pbx1 activity by promoting nuclear import of the Pbx1 protein; and that ectopic expression of Meis1 in chicken and hth in Drosophila disrupts distal limb development and induces distal-to-proximal transformations. We suggest that restriction of Meis1/Hth to proximal regions of the vertebrate and insect limb is essential to specify cell fates and differentiation patterns along the P-D axis of the limb.     

The Spectacle de la Nature in Eighteenth-Century Spain: From French Households to Spanish Workshops

This paper analyzes the Spanish appropriation of one of the great French eighteenth-century best-sellers, the Spectacle de la Nature (1732--1750) by the abbé Antoine Nöel Pluche. In eight volumes, the abbé discussed current issues in natural philosophy, such as Newtonianism, the origin of fossils, artisan techniques, natural history, machines, gardening or insect-collection in a polite-conversation format. It was translated into English (1735), Dutch (1737), Italian (1737), German (1746) and Spanish (1753). But the four Spanish editions were very different from their European counterparts. In Spain, it was delivered in 16 carefully printed and extensively commented volumes. In Pluche's original, there was a concern for the young gentleman's education, new pedagogical methods and an enthusiastic defence of experimental knowledge. However, Le Spectacle in Spain was conceived as a useful tool for modernizing the country, it served political and propagandist goals, defended Spanish culture and science (in particular with respect to American flora, fauna and geography) and the Jesuit contribution to science and aimed to harmonize experimental knowledge and scholastic tradition. The analysis of the more than 1500 footnotes, prefaces, some readers’ comments and other questions related to the format gives insight on how it was appropriated.