Cellular prion protein (PrP) modulates cell adhesion and signaling in the brain. Conversion to its infectious isoform causes neurodegeneration, including Creutzfeldt-Jakob disease in humans. PrP undergoes rapid plasma membrane turnover and extracellular release via exosomes. However, the intracellular transport of PrP and its potential impact on prion disease progression is barely understood. Here we identify critical components of PrP trafficking that also link intracellular and extracellular PrP turnover. PrP associates with muskelin, dynein, and KIF5C at transport vesicles. Notably, muskelin coordinates bidirectional PrP transport and facilitates lysosomal degradation over exosomal PrP release. Muskelin gene knockout consequently causes PrP accumulation at the neuronal surface and on secreted exosomes. Moreover, prion disease onset is accelerated following injection of pathogenic prions into muskelin knockout mice. Our data identify an essential checkpoint in PrP turnover. They propose a novel connection between neuronal intracellular lysosome targeting and extracellular exosome trafficking, relevant to the pathogenesis of neurodegenerative conditions.

We present a three-color femtosecond Er/Yb:fiber laser enabling highly specific and standardized nonlinear optical manipulation of live cells. The system simultaneously provides bandwidth-limited 80-fs pulses with identical intensity envelope centered at wavelengths of 515, 775, and 1035 nm in the focus of a confocal microscope. We achieve this goal by combining high-order dispersion control via, for example, chirped fiber Bragg gratings with proper bandwidth management in each nonlinear conversion step. Wavelength-selective and noninterfering induction of deoxyribonucleic acid (DNA) photoproducts and DNA strand breaks, as well as fluorescence photoactivation of a photoactivatable green fluorescent protein (PA-GFP)-histone fusion protein, are demonstrated. The capability to introduce different types of DNA lesions and perform photoswitching experiments in a selective manner is essential for quantitative studies on DNA repair and chromatin dynamics.

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