Final closure of the Paleo Asian Ocean basin in the early Triassic

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Abstract

The timing of the final welding of the southern Altaids to construct Pangea is a matter of debate which has led to considerable uncertainty regarding the configuration of northeast Pangea and the reconstruction of proto-Asia. Here we investigate the provenance of sediments deposited within a fore-arc accretionary basin located close to the Akeyazi low temperature ultra-high pressure metamorphic complex in the South Tianshan Orogenic Belt. Detrital zircon U-Pb analysis of sandstones yields a maximum depositional age in the early Triassic (around 231.7 million years ago) with a major early Permian peak and few Precambrian records. Bulk-rock composition and zircon Hf isotopic analysis, combined with a compilation of existing data, indicate the early Triassic sediment received additional detritus from the distal juvenile East Tianshan Arc region, rather than from any proximate tectonic units or an intra-oceanic arc. Available data suggests that the South Tianshan Ocean, an accessory ocean basin to the Paleo-Asian Ocean, could close in the early Triassic.

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Ultrastructural Characterization of the Lower Motor System in a Mouse Model of Krabbe Disease

Valentina Cappello, Laura Marchetti, Paola Parlanti … (2016)

Krabbe disease (KD) is a neurodegenerative disorder caused by the lack of β- galactosylceramidase enzymatic activity and by widespread accumulation of the cytotoxic galactosyl-sphingosine in neuronal, myelinating and endothelial cells. Despite the wide use of Twitcher mice as experimental model for KD, the ultrastructure of this model is partial and mainly addressing peripheral nerves. More details are requested to elucidate the basis of the motor defects, which are the first to appear during KD onset. Here we use transmission electron microscopy (TEM) to focus on the alterations produced by KD in the lower motor system at postnatal day 15 (P15), a nearly asymptomatic stage, and in the juvenile P30 mouse. We find mild effects on motorneuron soma, severe ones on sciatic nerves and very severe effects on nerve terminals and neuromuscular junctions at P30, with peripheral damage being already detectable at P15. Finally, we find that the gastrocnemius muscle undergoes atrophy and structural changes that are independent of denervation at P15. Our data further characterize the ultrastructural analysis of the KD mouse model, and support recent theories of a dying-back mechanism for neuronal degeneration, which is independent of demyelination.