bims-nucpor 2021-05-30 papers

Issue of 2021–05–30
three papers selected by
Sara Mingu, Johannes Gutenberg University

J Cell Sci. 2021 May 15. pii: jcs258340. [Epub ahead of print]134(10):

Integrity of the short arm of the nuclear pore Y-complex is required for mouse embryonic stem cell growth and differentiation.

Alba Gonzalez-Estevez, Annalisa Verrico, Clarisse Orniacki, Bernardo Reina-San-Martin, Valérie Doye.

Many cellular processes, ranging from cell division to differentiation, are controlled by nuclear pore complexes (NPCs). However, studying the contributions of individual NPC subunits to these processes in vertebrates has long been impeded by their complexity and the lack of efficient genetic tools. Here, we use genome editing in mouse embryonic stem cells (mESCs) to characterize the role of NPC structural components, focusing on the short arm of the Y-complex that comprises Nup85, Seh1 and Nup43. We show that Seh1 and Nup43, although dispensable in pluripotent mESCs, are required for their normal cell growth rates, their viability upon differentiation and for the maintenance of proper NPC density. mESCs with an N-terminally truncated Nup85 mutation (in which interaction with Seh1 is greatly impaired) feature a similar reduction of NPC density. However, their proliferation and differentiation are unaltered, indicating that it is the integrity of the Y-complex, rather than the number of NPCs, that is critical to ensure these processes.

Keywords: Mios; Mouse embryonic stem cells; Nucleoporin; Nup43; Nup85; Seh1

DOI: https://doi.org/10.1242/jcs.258340

Nucleus. 2021 Dec;12(1): 82-89

In vitro assembly of nuclear envelope in tobacco cultured cells.

Kentaro Tamura, Haruko Ueda, Ikuko Hara-Nishimura.

The coordinated regulation of the nucelar envelope (NE) reassembly during cell division is an essential event. However, there is little information on the molecular components involved in NE assembly in plant cells. Here we developed an in vitro assay of NE assembly using tobacco BY-2 cultured cells. To start the NE assembly reaction, the demembranated nuclei and the S12 fraction (cytosol and microsomes) were mixed in the presence of GTP and ATP nucleotides. Time-course analysis indicated that tubule structures were extended from the microsomal vesicles that accumulated on the demembranated nuclei, and finally sealed the NE. Immunofluorescence confirmed that the assembled membrane contains a component of nuclear pore complex. The efficiency of the NE assembly is significantly inhibited by GTPγS that suppresses membrane fusion. This in-vitro assay system may elucidate the role of specific proteins and provide important insights into the molecular machinery of NE assembly in plant cells.

Keywords: BY-2; confocal microscopy; endoplasmic reticulum; nuclear envelope; nucleus

DOI: https://doi.org/10.1080/19491034.2021.1930681

Biophys J. 2021 May 19. pii: S0006-3495(21)00419-7. [Epub ahead of print]

Modeling the role for nuclear import dynamics in the early embryonic cell cycle.

Yuki Shindo, Amanda A Amodeo.

Nuclear composition determines nuclear function. The early embryos of many species begin life with large pools of maternally-provided components that become rapidly imported into an increasing number of nuclei as the cells undergo repeated cleavage divisions. Since early cell cycles are too fast for nuclei to achieve steady-state nucleo-cytoplasmic partitioning, the composition of cleavage stage nuclei is likely dominated by nuclear import. The end of the rapid cleavage stage and onset of major zygotic transcription, known as the mid-blastula transition (MBT) is controlled by the ratio of nuclei to cytoplasm indicating that changes in nuclear composition likely mediate MBT timing. Here we explore how different nuclear import regimes can affect protein accumulation in the nucleus in the early Drosophila embryo. We find that nuclear import differs dramatically for a general nuclear cargo (NLS-mRFP) and a proposed MBT regulator (histone H3). We show that nuclear import rates of NLS-mRFP in a given nucleus remain relatively unchanged throughout the cleavage cycles while those of H3 halve with each cycle. We model these two distinct modes of nuclear import as "nucleus-limited" and "import-limited", and examine how the two different modes can contribute to different protein accumulation dynamics. Finally, we incorporate these distinct modes of nuclear import into a model for cell cycle regulation at the MBT and find that the import-limited H3 dynamics contribute to increased robustness and allow for stepwise cell cycle slowing at the MBT.

DOI: https://doi.org/10.1016/j.bpj.2021.05.005