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Results for “focused ion beam microscopy”

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PubMed2026

The trypanosome flagellum as model for parasitology, cell biology and ciliopathies.

Cilia and flagella exhibit widely conserved structures and functions across species. In humans, defects in these organelles are responsible for diseases called ciliopathies and many model organisms are used to study them. In this review, we will discuss one of them, the parasite Trypanosoma brucei, which is particularly well-suited to investigate general aspects of cilia and flagella, such as construction or protein localisation. Its flagellum remains present throughout the cell cycle, offering the opportunity to monitor flagellum maintenance and assembly within the same cell. This model organism is very convenient for flagellum live imaging as well as expansion microscopy and ultrastructural studies, including focused ion beam - scanning electron microscopy (FIB-SEM). Efficient tools exist to manipulate the genome, including endogenous tagging, inducible expression system, RNA interference and CRISPR-Cas9 approaches. Here, we review original contributions from studies in trypanosome to our understanding of flagellum construction and intraflagellar transport, as well as the impact of gene mutations in some ciliopathies.

Flagella↗

PubMed2016

Ultrastructure of early amelogenesis in wild-type, Amelx-/-, and Enam-/- mice: enamel ribbon initiation on dentin mineral and ribbon orientation by ameloblasts.

INTRODUCTION: Dental enamel is comprised of highly organized, oriented apatite crystals, but how they form is unclear. METHODS: We used focused ion beam (FIB) scanning electron microscopy (SEM) to investigate early enamel formation in 7-week-old incisors from wild-type, Amelx-/-, and Enam-/- C56BL/6 mice. FIB surface imaging scans thicker samples so that the thin enamel ribbons do not pass as readily out of the plane of section, and generates serial images by a mill and view approach for computerized tomography. RESULTS: We demonstrate that wild-type enamel ribbons initiate on dentin mineral on the sides and tips of mineralized collagen fibers, and extend in clusters from dentin to the ameloblast membrane. The clustering suggested that groups of enamel ribbons were initiated and then extended by finger-like membrane processes as they retracted back into the ameloblast distal membrane. These findings support the conclusions that no organic nucleator is necessary for enamel ribbon initiation (although no ribbons form in the Enam-/- mice), and that enamel ribbons elongate along the ameloblast membrane and orient in the direction of its retrograde movement. Tomographic reconstruction videos revealed a complex of ameloblast membrane processes and invaginations associated with intercellular junctions proximal to the mineralization front and also highlighted interproximal extracellular enamel matrix accumulations proximal to the interrod growth sites, which we propose are important for expanding the interrod matrix and extending interrod enamel ribbons. Amelx-/- mice produce oriented enamel ribbons, but the ribbons fuse into fan-like structures. The matrix does not expand sufficiently to support formation of the Tomes process or establish rod and interrod organization. CONCLUSION: Amelogenin does not directly nucleate, shape, or orient enamel ribbons, but separates and supports the enamel ribbons, and expands the enamel matrix to accommodate continued ribbon elongation, retrograde ameloblast movement, and rod/interrod organization.

Ameloblast↗

PubMed2025

The molecular basis of lamin-specific chromatin interactions.

In the cell nucleus, chromatin is anchored to the nuclear lamina, a network of lamin filaments and binding proteins that underly the inner nuclear membrane. The nuclear lamina is involved in chromatin organization through the interaction of lamina-associated domains within the densely packed heterochromatin regions. Using cryo-focused ion beam milling in conjunction with cryo-electron tomography, we analyzed the distribution of nucleosomes at the lamin-chromatin interface at the nanometer scale. Depletion of lamins A and C reduced nucleosome concentration at the nuclear periphery, while B-type lamin depletion contributed to nucleosome density in proximity to the lamina but not further away. We then investigated whether specific lamins can mediate direct interactions with chromatin. Using cryo-electron microscopy, we identified a specific binding motif of the lamin A tail domain that interacts with nucleosomes, distinguishing it from the other lamin isoforms. Furthermore, we examined chromatin structure dynamics using a genome-wide analysis that revealed lamin-dependent macroscopic-scale alterations in gene expression and chromatin remodeling. Our findings provide detailed insights into the dynamic and structural interplay between lamin isoforms and chromatin, molecular interactions that shape chromatin architecture and epigenetic regulation.

Nucleosomes↗