Use of human tissue to assess the oncogenic activity of melanoma-associated mutations

Multiple genetic alterations occur in melanoma, a lethal skin malignancy of increasing incidence. These include mutations that activate Ras and two of its effector cascades, Raf and phosphoinositide 3-kinase (PI3K). Induction of Ras and Raf can be caused by active N-Ras and B-Raf mutants as well as by gene amplification. Activation of PI3K pathway components occurs by PTEN loss and by AKT3 amplification. Melanomas also commonly show impairment of the p16(INK4A)-CDK4-Rb and ARF-HDM2-p53 tumor suppressor pathways. CDKN2A mutations can produce p16(INK4A) and ARF protein loss. Rb bypass can also occur through activating CDK4 mutations as well as by CDK4 amplification. In addition to ARF deletion, p53 pathway disruption can result from dominant negative TP53 mutations. TERT amplification also occurs in melanoma. The extent to which these mutations can induce human melanocytic neoplasia is unknown. Here we characterize pathways sufficient to generate human melanocytic neoplasia and show that genetically altered human tissue facilitates functional analysis of mutations observed in human tumors.     

The gonadotropic action of cecropia extracts in allatectomized American cockroaches

Résumé Les auteurs ont constaté que les extraits abdominaux de Phalènes mâles (Hyalophora cecropia) considérés comme une bonne source d'hormone juvénile, stimulent la croissance ovarienne et la formation du vitellus quand ils sont injectés à des femelles allatectomisées de la Blatte américaine (Periplaneta americana). Le farnésol, composé qui produit sur certains insectes les mêmes effets que l'hormone juvénile, a également une action gonadotrope définie lorsqu'on l'applique sur l'intégument de la Blatte.     

Identification of scrapie prion protein-specific mRNA in scrapie-infected and uninfected brain

To date no nucleic acid has been found in the purified infectious agent which causes the spongiform encephalopathy known as scrapie. In an attempt to identify a unique scrapie virus-associated messenger RNA in tissues of infected animals, we have synthesized an oligonucleotide probe complementary to the mRNA sequence corresponding to the amino-acid sequence of the prion protein, PrP27-30 (ref. 1). We report here that, with this probe, a complementary DNA clone representing PrP27-30 was obtained from scrapie-infected mouse brain; the DNA sequence of this clone could be translated into a protein that matches exactly the published sequence of PrP27-30. The cDNA clone hybridized to a single 2.4-2.5-kilobase (kb) mRNA from both normal and scrapie-infected brain. Thus, the PrP27-30 mRNA is not uniquely associated with scrapie infectivity, suggesting that PrP27-30 may be a normal component of mouse and hamster brain.     

Loss of cyclophilin D reveals a critical role for mitochondrial permeability transition in cell death

Mitochondria play a critical role in mediating both apoptotic and necrotic cell death. The mitochondrial permeability transition (mPT) leads to mitochondrial swelling, outer membrane rupture and the release of apoptotic mediators. The mPT pore is thought to consist of the adenine nucleotide translocator, a voltage-dependent anion channel, and cyclophilin D (the Ppif gene product), a prolyl isomerase located within the mitochondrial matrix. Here we generated mice lacking Ppif and mice overexpressing cyclophilin D in the heart. Ppif null mice are protected from ischaemia/reperfusion-induced cell death in vivo, whereas cyclophilin D-overexpressing mice show mitochondrial swelling and spontaneous cell death. Mitochondria isolated from the livers, hearts and brains of Ppif null mice are resistant to mitochondrial swelling and permeability transition in vitro. Moreover, primary hepatocytes and fibroblasts isolated from Ppif null mice are largely protected from Ca2+-overload and oxidative stress-induced cell death. However, Bcl-2 family member-induced cell death does not depend on cyclophilin D, and Ppif null fibroblasts are not protected from staurosporine or tumour-necrosis factor-alpha-induced death. Thus, cyclophilin D and the mitochondrial permeability transition are required for mediating Ca2+- and oxidative damage-induced cell death, but not Bcl-2 family member-regulated death.     

The breakdown of continuum models for mechanical contacts

Forces acting within the area of atomic contact between surfaces play a central role in friction and adhesion. Such forces are traditionally calculated using continuum contact mechanics, which is known to break down as the contact radius approaches atomic dimensions. Yet contact mechanics is being applied at ever smaller lengths, driven by interest in shrinking devices to nanometre scales, creating nanostructured materials with optimized mechanical properties, and understanding the molecular origins of macroscopic friction and adhesion. Here we use molecular simulations to test the limits of contact mechanics under ideal conditions. Our findings indicate that atomic discreteness within the bulk of the solids does not have a significant effect, but that the atomic-scale surface roughness that is always produced by discrete atoms leads to dramatic deviations from continuum theory. Contact areas and stresses may be changed by a factor of two, whereas friction and lateral contact stiffness change by an order of magnitude. These variations are likely to affect continuum predictions for many macroscopic rough surfaces, where studies show that the total contact area is broken up into many separate regions with very small mean radius.     

A difference in creatine uptake between pectoralis and thigh muscles of the chicken

Zusammenfassung Intravenös verabreichte Tracerdosis von¹⁴C-Kreatin führt beim Huhn zur viermal höheren Aufnahme im Biceps femoris als im Musculus pectoralis. Dieser muskuläre Unterschied fällt fort, wenn gleichzeitig grosse Mengen nicht-radioaktiven Kreatins gegeben werden.

---

---

Supported in part by United States Public Health Service Grant Nos. NSO6807 and HEO6312.