Biology subjects

Tait, J.

Publications and source records attributed to Tait, J..

3 recordsLinked to original sources

bioRxiv2025

Catalytic activity of KMT5B promotes cilia tuft formation without affecting chromatin accessibility of ciliary genes

Multiciliated cells are a specialized cell type found in the brain, reproductive tract and respiratory tract of mammals. Multiciliated cells resembling those of the mammalian lung can also be found on the surface of the epidermis of tadpole stage Xenopus embryos, making the frog an ideal model organism to study this cell type. KMT5B/suv4-20h1 is a histone methyltransferase that writes the dimethyl mark on histone 4, lysine 20 (H4K20). We have previously shown that the multiciliated cells of embryos lacking KMT5B have depleted cilia and a reduced actin cap, and that knockdown of both KMT5B and KMT5C/suv4-20h2 leads to downregulation of ciliogenic genes. Here we further tease out the independent function of KMT5B in multiciliogenesis, and show that single knockdown of KMT5B, but not KMT5C leads to aberrant transcription and the downregulation of cilia genes. This phenotype is ameliorated by overexpression of catalytically active PHF8, an H4K20me1 demethylase, while a hormone inducible variant of multicilin (MCI), the master regulator of cilia tuft formation, has no effect. Notably, the expression of key transcription factors of ciliogenesis is unaffected by KMT5B depletion, and the transcriptional effect of KMT5B depletion dominates the response to ectopic multicilin. Finally, ATAC seq analysis in animal caps reveals that knockdown of KMT5B results globally in very few peaks with differential activity and does not compact chromatin at ciliary genes. Taken together, this suggests that KMT5B regulates multiciliated cells through an alternative pathway to the canonical MCI-driven multiciliogenic program.

developmental biology↗

bioRxiv2020

Histone H4K20 methylation synchronizes cytoskeletal dynamics with cell cycle phases during epidermal differentiation

Histone tails are subject to various post-translational modifications, which play a fundamental role in altering chromatin accessibility. Although they are thought to regulate progression through development, the impact of the most abundant histone modification in vertebrates, i.e., histone H4 lysine 20 dimethylation (H4K20m2), has remained largely elusive. H4K20m2 arises from sequential methylation of new, unmodified histone H4 proteins, incorporated into chromatin during DNA replication, by the mono-methylating enzyme PR-SET7/KMT5A during G2/M phases, followed by conversion to the dimethylated state by SUV4-20H1 enzymes in the following G1/G0 phase. To address its function, we have blocked the deposition of this mark by depleting Xenopus embryos of SUV4-20H1/H2 methyltransferases, which convert H4K20 monomethylated to di- and tri-methylated states, respectively In the frog larval epidermis this results in a severe loss of cilia in multiciliated cells (MCC), a key component of all mucociliary epithelia. MCC precursor cells are correctly specified and amplify centrioles, but ultimately fail in ciliogenesis due to perturbation of cytoplasmic processes. Genome wide transcriptome profiling reveals that SUV4-20H1/H2 depleted ectodermal Animal Cap explants preferentially down-regulate the expression of several hundred cytoskeleton and cilium related genes as a consequence of persistent H4K20 monomethyl marks on postmitotic chromatin. Further analysis demonstrated that knockdown of SUV4-20H1 alone is sufficient to generate the MCC phenotype and that overexpression of the H4K20m1-specific histone demethylase PHF8 rescues the ciliogenic defect in significant, although partial, manner. Taken together, this indicates that the conversion of H4K20m1 to H4K20m2 by SUV4-20H1 is critical to synchronize cytoskeletal dynamics in concert with the cell cycle.

developmental biology↗

bioRxiv2020

The H3.3 chaperone Hira complex orchestrates oocyte developmental competence

Reproductive success relies on a healthy oocyte competent for fertilisation and capable of sustaining early embryo development. By the end of oogenesis, the oocyte is characterised by a transcriptionally silenced state, but the significance of this state and how it is achieved remains poorly understood. Histone H3.3, one of the H3 variants, has unique functions in chromatin structure and gene expression that are cell cycle-independent. We report here a comprehensive characterisation of the roles of the subunits of the Hira complex (i.e. Hira, Cabin1 and Ubn1), which is primarily responsible for H3.3 deposition during mouse oocyte development. Loss-of-function of any component of the Hira complex led to early embryogenesis failure. Transcriptome and nascent RNA analyses revealed that mutant oocytes fail to silence global transcription. Hira complex mutants are unable to establish the H3K4me3 and H3K9me3 repressive marks, resulting in aberrant chromatin accessibility. Among the misregulated genes in mutant oocytes is Zscan4, a 2-cell specific gene that is involved in zygote genome activation. Overexpression of Zscan4 recapitulates the phenotypes of Hira mutants, illustrating that temporal and spatial expression of Zscan4 is fine-tuned at the oocyte-to-embryo transition. Thus, the H3.3 chaperone Hira complex has a maternal effect function in oocyte developmental competence and early embryogenesis by modulating chromatin condensation and transcriptional quiescence.

developmental biology↗