MMX geodesy investigations: science requirements and observation strategy

In order to investigate the origin of Phobos and Deimos, the Japanese Martian Moons eXploration (MMX) mission is scheduled for launch in 2024. MMX will make comprehensive remote-sensing measurements of both moons and return regolith samples from Phobos to Earth. Geodetic measurements of gravity, shape, and rotation parameter of a body provides constraints on its internal structure reflecting its origin and evolution. Moments of inertia are important parameters to constrain the internal mass distribution, but they have not been well determined for the Martian moons yet. We discuss the mission requirements related to the moments of inertia to detect a potential heterogeneity of the mass distribution inside Phobos. We introduce mission instruments and operational strategies to meet the mission requirements. We present a preliminary imaging strategy from a quasi-satellite orbit for a base shape model that is expected to be created at the early stage of the mission. Geodetic products including ephemeris, gravity field, rotation parameter of Phobos, and spacecraft orbit are of importance not only for the geodetic study, but also for interpreting data from various mission instruments and selecting possible landing sites. Graphical Abstract

Nucleoporin TPR promotes tRNA nuclear export and protein synthesis in lung cancer cells

The robust proliferation of cancer cells requires vastly elevated levels of protein synthesis, which relies on a steady supply of aminoacylated tRNAs. Delivery of tRNAs to the cytoplasm is a highly regulated process, but the machinery for tRNA nuclear export is not fully elucidated. In this study, using a live cell imaging strategy that visualizes nascent transcripts from a specific tRNA gene in yeast, we identified the nuclear basket proteins Mlp1 and Mlp2, two homologs of the human TPR protein, as regulators of tRNA export. TPR expression is significantly increased in lung cancer tissues and correlated with poor prognosis. Consistently, knockdown of TPR inhibits tRNA nuclear export, protein synthesis and cell growth in lung cancer cell lines. We further show that NXF1, a well-known mRNA nuclear export factor, associates with tRNAs and mediates their transport through nuclear pores. Collectively, our findings uncover a conserved mechanism that regulates nuclear export of tRNAs, which is a limiting step in protein synthesis in eukaryotes.

Ratiometric 4Pi single molecule localization with optimal resolution and color assignment

4Pi single molecule localization microscopy (4Pi-SMLM) with two opposing objectives achieves sub-10 nm isotropic 3D resolution with as few as 250 photons collected by each objective. Here, we developed a new ratiometric multi-color imaging strategy for 4Pi-SMLM which employed the intrinsic multi-phase interference intensity without increasing the complexity of the system and achieved both optimal 3D resolution and color separation. By partially linking the photon parameters between channels with interference difference of π during global fitting of the multi-channel 4Pi single molecule data, we showed on simulated data that the loss of the localization precision is minimal compared with the theoretical minimum uncertainty, the Cramer-Rao lower bound (CRLB).

Nanoscale Imaging of Biomolecules using Molecule Anchorable Gel-enabled Nanoscale In-situ Fluorescence Microscopy

Expansion microscopy (ExM) is a powerful imaging strategy that offers a low-cost solution for nanoimaging with conventional microscopes by physically and isotropically magnifying preserved biological specimens embedded in a cross-linked water-swellable hydrogel. Current ExM protocols require prior treatment with specialized reactive anchoring chemicals to link specific labels and biomolecule classes to the gel. In addition, most techniques reportedly use strong Proteinase K to digest endogenous epitopes to enable expansion and are limited by using mechanically fragile gel formulas to expand specimens by at most 4.5× linearly. Here we describe a new ExM framework, Molecule Anchorable Gel-enabled Nanoscale In-situ Fluorescence MicroscopY (MAGNIFY), that uses a mechanically sturdy gel that enables broad retention of nucleic acids, proteins, and lipids without the need for a separate anchoring step. MAGNIFY expands biological specimens up to 11× and facilitates imaging of cells and tissues with effectively ~25-nm-resolution using an ∼280-nm diffraction-limited objective lens on conventional optical microscopes or with ~13 nm-resolution if combined with Super-resolution Optical Fluctuation Imaging (SOFI). Further, MAGNIFY generalizes well across a broad range of biological specimens, providing insight into nanoscopic subcellular structures including synaptic proteins from mouse brain, podocyte foot processes in human kidney, and defects in cilia and basal bodies in drug-treated human lung organoids. MAGNIFY provides a novel advance that expands the precision, utility, accessibility, and generality of subcellular nanoscopy.

Fluorescent Staining of Silicone Micro-and Nano-patterns for Their Optical Imaging

Performance of engineered surfaces can be enhanced by making them hydrophobic or superhydrophobic via coating them with low-surface-energy micro-and nano-patterns. However, the wetting phenomena of particularly irregular shape and spacing (super)hydrophobic patterns such as polysiloxane coatings are not yet fully understood from a microscopic perspective. Here, we show a new method to collect 3D confocal images from irregular polysiloxane micro-and nanorods from a single rod resolution to discuss their wetting response over long liquid/solid interaction times and quantify the length and diameter of these rods. To collect such 3D confocal images, fluorescent dye containing water droplets were left on our superhydrophobic and hydrophobic polysiloxane coated surfaces. Then their liquid/solid interfaces were imaged at different staining scenarios: (i) using different fluorescent dyes, (ii) when the droplets were in contact with surfaces, or (iii) after the droplets were taken away from the surface at the end of staining. Using such staining strategies, we could resolve the micro-and nanorods from root to top and determine their length and diameter, which were then found to be in good agreement with those obtained from their electron microscopy images. 3D confocal images in this paper, for the first time, present the long-time existence of more than one wetting state under the same droplet in contact with surfaces, as well as external and internal three-phase contact lines shifting and pinning. In the end, these findings were used to explain the time-dependent wetting kinetics of our surfaces. We believe that the proposed imaging strategy here will, in the future, be used to study many other irregular patterned (super)antiwetting surfaces to describe their wetting theory, which is today impossible due to the complicated surface geometry of these irregular patterns.