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The Andes between 28° and 30°S represent a transition between the Puna‐Altiplano Plateau and the Frontal/Principal Cordillera fold‐and‐thrust belts to the south. While significant early Cenozoic deformation documented in the Andean Plateau, deciphering the early episodes of deformation during Andean mountain building in the transition area is largely unstudied. Apatite fission track (AFT) and (U‐Th‐Sm)/He (AHe) thermochronology from a vertical and a horizontal transect reveal the exhumation history of the High Andes at 30°S, an area at the heart of this major transition. Interpretation of the age‐elevation profile, combined with inverse thermal modeling, indicates that the onset of rapid cooling was underway by ~35 Ma, followed by a significant decrease in cooling rate at ~30–25 Ma. AFT thermal models also reveal a second episode of rapid cooling in the early Miocene (~18 Ma) related to rock exhumation to its present position. Low exhumation between the rapid cooling events allowed for the development of a partial annealing zone. We interpret the observed Eocene rapid exhumation as the product of a previously unrecognized compressive event in this part of the Andes that reflects a southern extension of Eocene orogenesis recognized in the Puna/Altiplano. Renewed early‐Miocene exhumation indicates that the late Cenozoic compressional stresses responsible for the main phase of uplift of the South Central Andes also impacted the core of the range in this transitional sector. The major episode of Eocene exhumation suggests the creation of significant topographic relief in the High Andes earlier than previously thought. We investigate the exhumation history at the core of the Andes above the flat slab segment by performing AFT and (U‐Th)/He thermochronologyThe late Eocene constructional phase was recognized in the western and eastern limits of the High Andes (Frontal Cordillera) at 30°SWe propose a southern continuation of the Incaic relief from Puna/Altiplano through the latitude of 30°S

We have utilized electron paramagnetic resonance spectroscopy to study secondary structure, subunit interaction, and molecular orientation of vimentin molecules within intact intermediate filaments and assembly intermediates. Spectroscopy data prove alpha-helical coiled-coil structures at individual amino acids 316-336 located in rod 2B. Analysis of positions 305, 309, and 312 identify this region as conforming to the helical pattern identified within 316-336 and thus demonstrates that, contrary to some previous predictions, this region is in an alpha-helical conformation. We show that by varying the position of the spin label, we can identify both intra- and inter-dimer interactions. With a label attached to the outside of the alpha-helix, we have been able to measure interactions between positions 348 of separate dimers as they align together in intact filaments, identifying the exact point of overlap. By mixing different spin-labeled proteins, we demonstrate that the interaction at position 348 is the result of an anti-parallel arrangement of dimers. This approach provides high resolution structural information (<2 nm resolution), can be used to identify molecular arrangements between subunits in an intact intermediate filament, and should be applicable to other noncrystallizable filamentous systems as well as to the study of protein fibrils.

Although single-channel and whole-cell patch-clamp recordings have demonstrated the presence of Na+ currents in retinal ganglion cell somata, it has not previously been reported that an anti-Na+-channel antiserum stains both retinal ganglion cell somata and proteins with molecular weights corresponding to complexes of α and β subunits. We probed adult goldfish retinas for Na+ channel-like immunoreactivity with a polyclonal antibody directed against the EOIII segment of vertebrate voltage-gated Na+ channels. In vertical sections and whole mounts, this antibody consistently stained the somata, axons, and proximal dendrites of retinal ganglion cells. Some somata in the proximal third of the inner nuclear layer were also stained. In Western blots, this antibody specifically stained multiple protein bands from retina and optic nerve, all with apparent molecular weights between 200 and 315 kDa. The largest of these molecular weights agrees with that reported previously for complexes of α and β subunits in mammalian neurons, including retinal ganglion cells. The intermediate and lowest molecular weights are consistent with the presence of multiple Na+ channel α subunits, either in individual proximal retinal neurons or in different morphological subtypes.

Several letters to the editor are presented in response to articles in previous issues including "Why Young Voters Care Again," February 11, 2008, the article by Michael Duffy and Mark Kukis on why the surge in Iraq has worked, February 11, 2008, and "Trouble Woman," by Josh Tyrangiel, February 4, 2008.

The cells of the eye lens contain the type III intermediate filament protein vimentin, as well as two other intermediate filament proteins, CP49 and filensin. These two proteins appear to be unique to the differentiated lens fibre cell. Immunoblotting and confocal microscopy were used to describe changes which occur in these three intermediate filament proteins and the networks they form during fibre cell differentiation and maturation. The vimentin network was present in both epithelial cells and some fibre cells. Fibre cells were vimentin positive up to a specific point 2-3 mm in from the lens capsule where the vimentin signal was drastically reduced. The CP49/filensin network was not present in the undifferentiated epithelial cells but emerged in the differentiating fibre cells. This latter network exhibited a principally plasma membrane localization in younger fibre cells but became more cytoplasmic in older fibre cells. This change also occurred at a distinct point in fibre cell differentiation, much earlier than the observed loss of the vimentin network. The subcellular changes in the distributions of these cytoskeletal networks were correlated to the loss of the fibre cell nucleus, another feature of fibre cell differentiation. No correlation was found to changes in the vimentin network but nuclear loss did coincide with changes in the CP49/filensin network. Concomitant with nuclear pyknosis, there were also changes in the nuclear lamina as well as infringement of the nuclear compartment by CP49, as shown by confocal microscopy. This study demonstrates vimentin and the CP49/filensin network to be independent in the lens but both networks undergo dramatic changes in subcellular distribution during the differentiation/maturation of the fibre cell. Only changes in the CP49/filensin network can be correlated to nuclear loss. Thus in the lens, unlike mammalian erythropoiesis which is also characterized by nuclear loss, the vimentin network does not appear linked to nuclear retention.

Xcat is a recently identified mouse mutation causing X-linked dominant congenital cataract. The mutation is of particular interest as a possible animal model for the human X-linked cataract syndrome. Using light microscopy, we examined the histological changes of mutant lenses at selected intervals between embryonic (E) day 14 and postnatal (P) day 21. At E14, primary fiber formation completely fills the former lens vesicle in both normal and mutant mice, but in affected animals the primary fibers are irregularly arranged and show small foci of cellular disintegration. Progressive degeneration of primary fibers occurs from E15 to E18 and, during late gestation, secondary lens fibers also begin to degenerate. The lens epithelium and newly differentiated fibers, however, show no evident abnormality. Postnatally, most of the lens substance becomes amorphous; the cataractous process terminates in rupture of the posterior lens capsule by P21. Analysis of crystallin and cytoskeletal proteins of postnatal cataractous lenses revealed no significant abnormalities when compared to normal lenses. The observed sequence of histological changes indicates that the Xcat mutation affects the differentiation of lens fiber cells at some point after their initial elongation. Copyright 1993, 1999 Academic Press

The ocular lens fiber cell assembles a novel cytoskeletal element, the Beaded Filament, from CP49 and filensin, two proteins expressed only in the differentiated lens fiber cell. We report the primary sequence, secondary structural analysis, gene structure and Yeast Two Hybrid interaction data for human filensin, and develop a consensus model of filensin from the human and previously reported bovine and chicken filensin sequences. This consensus model, combined with gene structure and Yeast Two Hybrid studies establish that filensin is a member of the Intermediate Filament family of proteins. Specifically, filensin exhibits (1) divergence at amino acid sequence motifs otherwise highly conserved among intermediate filament proteins, (2) a loss of 29 amino acids from the central rod domain which is unique among cytoplasmic intermediate filament proteins, (3) an absence of sequence identity with any existing class of intermediate filament protein, (4) a gene structure unique among intermediate filament family, (5) an inability to dimerize with representatives of Type I, II, and III intermediate filament proteins. Thus, at each level of analysis, we find that filensin is similar to the consensus model of intermediate filament proteins, supporting our conclusion that filensin's relatedness to the IF family is not the consequence of convergent evolution. However, filensin also shows unique or extreme distinctions from the consensus intermediate filament protein at each level of analysis, indicating that filensin constitutes a novel class of IF protein. Some of filensin's unique features are incompatible with current models of IF assembly. Analysis of filensin gene structure suggests that the 29 amino acid reduction in the central rod domain was not the result of a single splice site mutation, the mechanism suggested for the transition between nuclear lamins and cytoplasmic intermediate filament proteins.

Several letters to the editor are presented in response to articles in previous issues, including one on the relationship between scientific research and sexual relationships, one on the reputation of Presidential candidate John McCain, and one on the death of "Brokeback Mountain" star Heath Ledger, all in the February 25, 2008 issue.