Hidetoshi Urakubo

This study developed a three-dimensional ultrastructural analysis application using serial block-face scanning electron microscopy (SBF-SEM) to investigate surgically acquired human skin tissues containing the arrector pili muscle. We utilized the en bloc staining, including reduced osmium, thiocarbohydrazide, and lead aspartate, as well as the embedding using a carbon-based conductive resin. Next, we obtained serial images with SBF-SEM. The results revealed dense nerve fiber networks branching from nearby nerve fiber bundles outside the muscle and running among muscle fibers. Additionally, the dense nerve network running through and along arrector pili muscle fibers rarely penetrates the connective tissues between smooth muscle fibers and epithelial cells. Furthermore, in the observation area, no individual smooth muscle fibers formed adhesion structures with the epithelial cells of the hair follicle, ending in the dermal extracellular matrix near the epithelial cells. These results indicate the usefulness of this approach for three-dimensional ultrastructural analyses of human skin tissues comprising follicular units and revealing structural changes in skin tissues, especially the arrector pili muscle and nerve fibers with hair follicular epithelium, in aging and diseased conditions.

Abstract Liquid–liquid phase separation (LLPS) of biological macromolecules leads to the formation of various membraneless organelles. LLPS can not only form homogenous condensates but also multilayered and multiphase condensates, which can mediate complex cellular functions. However, the factors that determine the topological features of multiphase condensates are not fully understood. Herein, we focused on Ca²⁺/calmodulin-dependent protein kinase II (CaMKII), a major postsynaptic protein that undergoes various forms of LLPS with other postsynaptic proteins, and present a minimalistic computational model that reproduces these forms of LLPS, including a form of two-phase condensates, phase-in-phase (PIP) organization. Analyses of this model revealed that the competitive binding of two types of client proteins is required for the PIP formation. The PIP only formed when CaMKII had high valency and a short linker length. Such CaMKII proteins exhibited a low surface tension, a modular structure, and slow diffusion. These properties are consistent with the functions required by CaMKII to store information at the synaptic level. Thus, the computational modeling reveals new structure–function relationships for CaMKII as a synaptic memory unit.

Abstract Background and Aims During the analysis of plant male meiocytes coming from destroyed meiocyte columns (united multicellular structures formed by male meiocytes in each anther locule), a considerable amount of information becomes unavailable. Therefore, in this study intact meiocyte columns were studied by volume microscopy in wild-type rye for the most relevant presentation of 3-D structure of rye meiocytes throughout meiosis. Methods We used two types of volume light microscopy: confocal laser scanning microscopy and non-confocal bright-field scanning microscopy combined with alcohol and aldehyde fixation, as well as serial block-face scanning electron microscopy. Key Results Unusual structures, called nuclear protuberances, were detected. At certain meiotic stages, nuclei formed protuberances that crossed the cell wall through intercellular channels and extended into the cytoplasm of neighbouring cells, while all other aspects of cell structure appeared to be normal. This phenomenon of intercellular nuclear migration (INM) was detected in most meiocytes at leptotene/zygotene. No cases of micronucleus formation or appearance of binucleated meiocytes were noticed. There were instances of direct contact between two nuclei during INM. No influence of fixation or of mechanical impact on the induction of INM was detected. Conclusions Intercellular nuclear migration in rye may be a programmed process (a normal part of rye male meiosis) or a tricky artefact that cannot be avoided in any way no matter which approach to meiocyte imaging is used. In both cases, INM seems to be an obligatory phenomenon that has previously been hidden by limitations of common microscopic techniques and by 2-D perception of plant male meiocytes. Intercellular nuclear migration cannot be ignored in any studies involving manipulations of rye anthers.