White dwarf stars with carbon atmospheres

White dwarfs represent the endpoint of stellar evolution for stars with initial masses between approximately 0.07 and 8-10, where is the mass of the Sun (more massive stars end their life as either black holes or neutron stars). The theory of stellar evolution predicts that the majority of white dwarfs have a core made of carbon and oxygen, which itself is surrounded by a helium layer and, for approximately 80 per cent of known white dwarfs, by an additional hydrogen layer. All white dwarfs therefore have been traditionally found to belong to one of two categories: those with a hydrogen-rich atmosphere (the DA spectral type) and those with a helium-rich atmosphere (the non-DAs). Here we report the discovery of several white dwarfs with atmospheres primarily composed of carbon, with little or no trace of hydrogen or helium. Our analysis shows that the atmospheric parameters found for these stars do not fit satisfactorily in any of the currently known theories of post-asymptotic giant branch evolution, although these objects might be the cooler counterpart of the unique and extensively studied PG 1159 star H1504+65 (refs 4-7). These stars, together with H1504+65, might accordingly form a new evolutionary sequence that follows the asymptotic giant branch.     

Body plan innovation in treehoppers through the evolution of an extra wing-like appendage

Body plans, which characterize the anatomical organization of animal groups of high taxonomic rank, often evolve by the reduction or loss of appendages (limbs in vertebrates and legs and wings in insects, for example). In contrast, the addition of new features is extremely rare and is thought to be heavily constrained, although the nature of the constraints remains elusive. Here we show that the treehopper (Membracidae) 'helmet' is actually an appendage, a wing serial homologue on the first thoracic segment. This innovation in the insect body plan is an unprecedented situation in 250 Myr of insect evolution. We provide evidence suggesting that the helmet arose by escaping the ancestral repression of wing formation imparted by a member of the Hox gene family, which sculpts the number and pattern of appendages along the body axis. Moreover, we propose that the exceptional morphological diversification of the helmet was possible because, in contrast to the wings, it escaped the stringent functional requirements imposed by flight. This example illustrates how complex morphological structures can arise by the expression of ancestral developmental potentials and fuel the morphological diversification of an evolutionary lineage.     

Localisation d'une glycoprotéine tissulaire du rat dans les cellules de la lignée myéloblastique

Summary It is shown by the method of enzyme antibody tagging technique that a rat tissue glycoprotein is located in the cytoplasm of cells of myeloblastic origin.

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Travail subventionné par le Conseil des Recherches Médicales du Canada.     

Distinction entre les variations phénotypiques sexuelles et génétiques chez le Rat,par l'analyse immunoélectrophorétique des protéines urinaires spécifiques

Summary We show that phenotypical variations of rat urinary proteins are either sex-linked (variations at the rho-uroprotein and major urinary protein level) or related to the genetic purity (variations at the -uroprotein level).

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Travail subventionné par l'octroi n 362-10 du Conseil des Recherches médicales du Canada.     

Polymorphisme des lipoprotéines et des glycoprotéines sériques chez la Truite

Summary It is shown that there are important differences among the serum proteins of 3 different species of trout. We stress that these genetic variations concern the lipoproteins as well as the glycoproteins. Furthermore, 3 serum proteins ofEsox lucius have antigenic determinants common with the serum proteins ofS. gairdneri; they are an ₂-lipoprotein, an ₂-glycoprotein and a -globulin.