Abstract
Histone modification and nucleosome assembly are mainly regulated by various histone-modifying enzymes and chaperones. The roles of histone-modification enzymes have been well analyzed, but the molecular mechanism of histone chaperones in histone modification and nucleosome assembly is incompletely understood. We previously found that the histone chaperone Nrp1 is localized in the micronucleus (MIC) and the macronucleus (MAC) and involved in the chromatin stability and nuclear division of Tetrahymena thermophila. In the present work, we found that truncated C-terminal mutant HA-Nrp1TrC abnormally localizes in the cytoplasm. The truncated-signal-peptide mutants HA-Nrp1TrNLS1 and HA-Nrp1TrNLS2 are localized in the MIC and MAC. Overexpression of Nrp1TrNLS1 inhibited cellular proliferation and disrupted micronuclear mitosis during the vegetative growth stage. During sexual development, Nrp1TrNLS1 overexpression led to abnormal bouquet structures and meiosis arrest. Furthermore, Histone H3 was not transported into the nucleus; instead, it formed an abnormal speckled cytoplastic distribution in the Nrp1TrNLS1 mutants. The acetylation level of H3K56 in the mutants also decreased, leading to significant changes in the transcription of the genome of the Nrp1TrNLS1 mutants. The histone chaperone Nrp1 regulates the H3 nuclear import and acetylation modification of H3K56 and affects chromatin stability and genome transcription in Tetrahymena.
Highlights
The genome of the eukaryotic cell is packaged into chromatin
Human nuclear autoantigenic sperm protein (NASP) occurs in two major forms, namely tNASP, which is found in gametes, embryonic cells, and transformed cells; and sNASP, which is found in all rapidly dividing somatic cells
The C-terminal domain of tNASP contains only one nuclear localization signals (NLS), and the NLS deletion mutant is retained in the cytoplasm [44]
Summary
The genome of the eukaryotic cell is packaged into chromatin. dynamic changes in chromatin structure and composition could potentially affect the function of genomes. Histone chaperones regulate histone assembly and disassembly [3], promote the interaction of new histones with other chaperones [4], mediate histone epigenetic modification [5], participate in ATP-dependent nucleosome remodeling [6], and regulate histone exchange during transcription [7]. These chaperones provide the functional complexity of nucleosomes by incorporating histone variants and combinatorial post-translational modifications (PTMs), which precisely regulate gene expression and the nuclear architecture. In HeLa cells, canonical histone H3 is deposited into the genome with the assistance of the histone chaperone CAF-1 complexes via replication-coupled nucleosome assembly (RC).
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