Evanescent light excitation is widely used in super-resolution fluorescence microscopy to confine light and reduce background noise.Herein we propose a method of exploiting evanescent light in the context of emission. When a fluorophore is located in close proximity to a medium with a higher refractive index, its near-field component is converted into light that propagates beyond the critical angle. This so-called Supercritical-Angle Fluorescence (SAF) can be captured using a high-NA objective and used to determine the axial position of the fluorophore with nanometer precision. We introduce a new technique for 3D nanoscopy that combines direct STochastic Optical Reconstruction Microscopy (dSTORM) imaging with dedicated detection of SAF emission. We demonstrate that our approach of a Direct Optical Nanoscopy with Axially Localized Detection (DONALD) yields a typical isotropic 3D localization precision of 20-nm. 2Super-localization methods in optical microscopy such as PALM, (F)PALM and dSTORM, have shattered the spatial resolution barrier imposed by the diffraction limit. These techniques are based on the sequential detection of several thousands individual fluorescent molecules [1,2,3,4]. In their simplest implementations, these methods typically improve lateral resolution by one order of magnitude, however their axial resolution is still limited by diffraction. Specific techniques must be developped to tackle this strong anisotropy resolution, which compromises 3D imaging. Super-localization techniques must be combined with Point Spread Function (PSF) engineering methods, to measure the depth position of each detected fluorophore [5,6,7,8,9]. Single-[5] and double- [7] cylindrical-lens methods have achieved axial-localization precisions 60 and 20 nm, respectively. The former is very stable and straightforward to implement, whereas the higher precision of the latter comes at the cost of increased complexity. Similarly, alternative elaborate methods such as interferometric PALM (iPALM) [10] and the SelfBending PSF (SB-PSF) [11] can achieve axial localization precision of 10 nm and 15 nm, respectively [12]. In addition, all these strategies provide only the relative axial positions of the fluorophores with respect to an arbitrary focal plane. Hence, 3D optical nanoscopy is in need of a method that combines high nanometer axial precision, simplicity of implementation and absolute axial positioning.Herein we report a new approach termed "Direct Optical Nanoscopy with This dipole is also endowed with a non propagative near field component that depends on the surrounding refractive index n m . In the presence of an interface with a medium with a refractive index of n g > n m , the transmitted light follows Snell-Decartes law of refraction (Fig. 1a). The refracted light is emitted within a cone that is limited by the critical angle θ c = arcsin (n m /n g ). Plane (BFP). These aplanetic objectives satisfy Abbe sine relation: light emitted with an angle θ lies within a circle of radius ρ = nf sin(θ) in the BFP where n...

Cleavage of mutant huntingtin (HTT) is an essential process in Huntington's disease (HD), an inherited neurodegenerative disorder. Cleavage generates N-ter fragments that contain the polyQ stretch and whose nuclear toxicity is well established. However, the functional defects induced by cleavage of full-length HTT remain elusive. Moreover, the contribution of non-polyQ C-terminal fragments is unknown. Using time-and site-specific control of full-length HTT proteolysis, we show that specific cleavages are required to disrupt intramolecular interactions within HTT and to cause toxicity in cells and flies. Surprisingly, in addition to the canonical pathogenic N-ter fragments, the C-ter fragments generated, that do not contain the polyQ stretch, induced toxicity via dilation of the endoplasmic reticulum (ER) and increased ER stress. C-ter HTT bound to dynamin 1 and subsequently impaired its activity at ER membranes. Our findings support a role for HTT on dynamin 1 function and ER homoeostasis. Proteolysis-induced alteration of this function may be relevant to disease.