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Diffusion of large molecules into assembling nuclei revealed using an optical highlighting technique.

ABSTRACT: The nuclear envelope (NE) defines the nuclear compartment, and nuclear pore complexes (NPCs) on the NE form aqueous passages through which small water-soluble molecules can passively diffuse. It is well known that proteins smaller than 50 kDa can diffuse though NPCs, whereas proteins larger than 60 kDa rarely enter by passive diffusion. Little, however, is known about how this size cutoff develops as the NE reassembles and the nucleus expands. In 1987, a well-known study identified an efficient mechanism by which large diffusing proteins (> 60 kDa) were excluded from the reassembling nucleus after mitosis. Since then, it has been generally accepted that after mitosis, newly formed nuclei completely exclude all proteins except those that are initially bound to the mitotic chromosomes and those that are selectively imported through NPCs. Here, the tetrameric complex of the photoconvertible fluorescent protein KikGR ( approximately 103 kDa) was optically highlighted in the cytoplasm and followed to examine its entry into nuclei. Remarkably, highlighted complexes efficiently entered newly assembled nuclei during an approximately 20-min period after the completion of cytokinesis. Because KikGR contains no known nuclear-localization or chromosome-binding sequences, our results indicate the diffusion barrier is less restrictive during nuclear reassembly.

SUBMITTER: Shimozono S

PROVIDER: S-EPMC2749756 | biostudies-literature | 2009 Sep

REPOSITORIES: biostudies-literature

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Diffusion of large molecules into assembling nuclei revealed using an optical highlighting technique.

Shimozono Satoshi S Tsutsui Hidekazu H Miyawaki Atsushi A

Biophysical journal 20090901 5

The nuclear envelope (NE) defines the nuclear compartment, and nuclear pore complexes (NPCs) on the NE form aqueous passages through which small water-soluble molecules can passively diffuse. It is well known that proteins smaller than 50 kDa can diffuse though NPCs, whereas proteins larger than 60 kDa rarely enter by passive diffusion. Little, however, is known about how this size cutoff develops as the NE reassembles and the nucleus expands. In 1987, a well-known study identified an efficient ...[more]

PMID: 19720016

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Project description:The human thalamus is a highly connected brain structure, which is key for the control of numerous functions and is involved in several neurological disorders. Recently, neuroimaging studies have increasingly focused on the volume and connectivity of the specific nuclei comprising this structure, rather than looking at the thalamus as a whole. However, accurate identification of cytoarchitectonically designed histological nuclei on standard in vivo structural MRI is hampered by the lack of image contrast that can be used to distinguish nuclei from each other and from surrounding white matter tracts. While diffusion MRI may offer such contrast, it has lower resolution and lacks some boundaries visible in structural imaging. In this work, we present a Bayesian segmentation algorithm for the thalamus. This algorithm combines prior information from a probabilistic atlas with likelihood models for both structural and diffusion MRI, allowing segmentation of 25 thalamic labels per hemisphere informed by both modalities. We present an improved probabilistic atlas, incorporating thalamic nuclei identified from histology and 45 white matter tracts surrounding the thalamus identified in ultra-high gradient strength diffusion imaging. We present a family of likelihood models for diffusion tensor imaging, ensuring compatibility with the vast majority of neuroimaging datasets that include diffusion MRI data. The use of these diffusion likelihood models greatly improves identification of nuclear groups versus segmentation based solely on structural MRI. Dice comparison of 5 manually identifiable groups of nuclei to ground truth segmentations show improvements of up to 10 percentage points. Additionally, our chosen model shows a high degree of reliability, with median test-retest Dice scores above 0.85 for four out of five nuclei groups, whilst also offering improved detection of differential thalamic involvement in Alzheimer's disease (AUROC 81.98%). The probabilistic atlas and segmentation tool will be made publicly available as part of the neuroimaging package FreeSurfer (https://freesurfer.net/fswiki/ThalamicNucleiDTI).

Dataset Information

Diffusion of large molecules into assembling nuclei revealed using an optical highlighting technique.

Publications

Diffusion of large molecules into assembling nuclei revealed using an optical highlighting technique.

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