Endoreduplication, the duplication of the nuclear genome without mitosis, is a common process in plants, especially in angiosperms and mosses. Accumulating evidence supports the relationship between ...endoreduplication and plastic responses to stress factors. Here, we investigated the level of endoreduplication in Ceratodon (Bryophyta), which includes the model organism Ceratodon purpureus.
We used flow cytometry to estimate the DNA content of 294 samples from 67 localities and found three well-defined cytotypes, two haploids and one diploid, the haploids corresponding to C. purpureus and Ceratodon amazonum, and the diploid to Ceratodon conicus, recombination occurring between the former two.
The endoreduplication index (EI) was significantly different for each cytotype, being higher in the two haploids. In addition, the EI of the haploids was higher during the hot and dry periods typical of the Mediterranean summer than during spring, whereas the EI of the diploid cytotype did not differ between seasons.
Endopolyploidy may be essential in haploid mosses to buffer periods of drought and to respond rapidly to desiccation events. Our results also suggest that the EI is closely related to the basic ploidy level, but less so to the nuclear DNA content as previously suggested.
Polyploid cells have genomes that contain multiples of the typical diploid chromosome number and are found in many different organisms. Studies in a variety of animal and plant developmental systems ...have revealed evolutionarily conserved mechanisms that control the generation of polyploidy and have recently begun to provide clues to its physiological function. These studies demonstrate that cellular polyploidy plays important roles during normal development and also contributes to human disease, particularly cancer.
Anaplastic thyroid cancer (ATC) is among the most lethal malignancies. The mitotic kinase PLK1 is overexpressed in the majority of ATCs and PLK1 inhibitors have shown preclinical efficacy. However, ...they also cause mitotic slippage and endoreduplication, leading to the generation of tetraploid, genetically unstable cell populations.
We hypothesized that PI3K activity may facilitate mitotic slippage upon PLK1 inhibition, and thus tested the effect of combining PLK1 and PI3K inhibitors in ATC models, in vitro and in vivo. Treatment with BI6727 and BKM120 resulted in a significant synergistic effect in ATC cells, independent of the levels of AKT activity. Combination of the two drugs enhanced growth suppression at doses for which the single drugs showed no effect, and led to a massive reduction of the tetraploid cells population. Furthermore, combined treatment in PI3Khigh cell lines showed a significant induction of apoptosis.
Finally, combined inhibition of PI3K and PLK1 was extremely effective in vivo, in an immunocompetent allograft model of ATC.
Our results demonstrate a clear therapeutic potential of combining PLK1 and PI3K inhibitors in anaplastic thyroid tumors.
•ATC is one of the most lethal tumor types, with a median survival of less than 6 months from diagnosis.•PLK1 is a mitotic regulator overexpressed in ATC, and the PI3K cascade is constitutively activated in 40% of ATCs.•ATC cells treated with a PLK1 inhibitor often evade cell cycle arrest and death via mitotic slippage and endoreduplication.•PI3K and PLK1 inhibition synergize in vitro, preventing slippage and inducing apoptosis, and potently cooperate in vivo.
Design of a synthetic yeast genome Richardson, Sarah M.; Mitchell, Leslie A.; Stracquadanio, Giovanni ...
Science (American Association for the Advancement of Science),
03/2017, Letnik:
355, Številka:
6329
Journal Article
Recenzirano
Odprti dostop
We describe complete design of a synthetic eukaryotic genome, Sc2.0, a highly modified Saccharomyces cerevisiae genome reduced in size by nearly 8%, with 1.1 megabases of the synthetic genome ...deleted, inserted, or altered. Sc2.0 chromosome design was implemented with BioStudio, an open-source framework developed for eukaryotic genome design, which coordinates design modifications from nucleotide to genome scales and enforces version control to systematically track edits. To achieve complete Sc2.0 genome synthesis, individual synthetic chromosomes built by Sc2.0 Consortium teams around the world will be consolidated into a single strain by “endoreduplication intercross.” Chemically synthesized genomes like Sc2.0 are fully customizable and allow experimentalists to ask otherwise intractable questions about chromosome structure, function, and evolution with a bottom-up design strategy.
SUMMARY
Endoreduplication, during which cells increase their DNA content through successive rounds of full genome replication without cell division, is the major source of endopolyploidy in higher ...plants. Endoreduplication plays pivotal roles in plant growth and development and is associated with the activation of specific transcriptional programmes that are characteristic of each cell type, thereby defining their identity. In plants, endoreduplication is found in numerous organs and cell types, especially in agronomically valuable ones, such as the fleshy fruit (pericarp) of tomato presenting high ploidy levels. We used the tomato pericarp tissue as a model system to explore the transcriptomes associated with endoreduplication progression during fruit growth. We confirmed that expression globally scales with ploidy level and identified sets of differentially expressed genes presenting only developmental‐specific, only ploidy‐specific expression patterns or profiles resulting from an additive effect of ploidy and development. When comparing ploidy levels at a specific developmental stage, we found that non‐endoreduplicated cells are defined by cell division state and cuticle synthesis while endoreduplicated cells are mainly defined by their metabolic activity changing rapidly over time. By combining this dataset with publicly available spatiotemporal pericarp expression data, we proposed a map describing the distribution of ploidy levels within the pericarp. These transcriptome‐based predictions were validated by quantifying ploidy levels within the pericarp tissue. This in situ ploidy quantification revealed the dynamic progression of endoreduplication and its cell layer specificity during early fruit development. In summary, the study sheds light on the complex relationship between endoreduplication, cell differentiation and gene expression patterns in the tomato pericarp.
Significance Statement
The progression of endoreduplication is very dynamic during early fruit development and displays cell layer‐specific patterns. The integration of ploidy distribution maps with ploidy‐specific transcriptome data revealed that gene expression in the pericarp is controlled both in a ploidy‐specific and developmental‐specific manner during the early stages of tomato fruit development, resulting in the spatialization of transcriptional programmes.
•A DNA endoploidy map of the Arabidopsis root reveals a strict spatio-temporal regulation of endoreplication.•Endoreplication is prominent in tissues that require a rapid increase in cell wall ...materials, such as root hairs and xylem.•Endoreplication-dependent cell wall modifications might account for the pathogen sensitivity of ploidy mutants.•Endocycle onset correlates with expression of cell wall-modifying genes that drive cell expansion.
Endoreplication represents a variant of the mitotic cell cycle during which cells replicate their DNA without mitosis and/or cytokinesis, resulting in an increase in the cells’ ploidy level. This process is especially prominent in higher plants, where it has been correlated with cell differentiation, metabolic output and rapid cell growth. However, different reports argue against a ploidy-dependent contribution to cell growth. Here, we review accumulating data suggesting that endocycle onset might exert an effect on cell growth through transcriptional control of cell wall-modifying genes to drive cell wall changes required to accommodate turgor-driven rapid cell expansion, consistent with the idea that vacuolar expansion rather than a ploidy-driven increase in cellular volume represents the major force driving cell growth.
Growth and developmental processes are occasionally accompanied by multiple rounds of DNA replication, known as endoreduplication. Coordination between endoreduplication and cell size regulation ...often plays a crucial role in proper organogenesis and cell differentiation. Here, we report that the level of correlation between ploidy and cell volume is different in the outer and inner cell layers of leaves of Arabidopsis thaliana using a novel imaging technique. Although there is a well-known, strong correlation between ploidy and cell volume in pavement cells of the epidermis, this correlation was extremely weak in palisade mesophyll cells. Induction of epidermis cell identity based on the expression of the homeobox gene ATML1 in mesophyll cells enhanced the level of correlation between ploidy and cell volume to near that of wild-type epidermal cells. We therefore propose that the correlation between ploidy and cell volume is regulated by cell identity.
Endoreduplication, a process in which DNA replication occurs in the absence of mitosis, is found in all eukaryotic kingdoms, especially plants, where it is assumed to be important for cell growth and ...cell fate maintenance. However, a comprehensive understanding of the mechanism regulating endoreduplication is still lacking. We previously reported that UBIQUITIN-SPECIFIC PROTEASE14 (UBP14), encoded by DA3, acts upstream of CYCLIN-DEPENDENT KINASE B1;1 (CDKB1;1) to influence endoreduplication and cell growth in Arabidopsis thaliana. The da3-1 mutant possesses large cotyledons with enlarged cells due to high ploidy levels. Here, we identified a suppressor of da3-1 (SUPPRESSOR OF da3-1 6; SUD6), encoding CYCLIN-DEPENDENT KINASE G2 (CDKG2), which promotes endoreduplication and cell growth. CDKG2/SUD6 physically associates with CDKB1;1 in vivo and in vitro. CDKB1;1 directly phosphorylates SUD6 and modulates its stability. Genetic analysis indicated that SUD6 acts downstream of DA3 and CDKB1;1 to control ploidy level and cell growth. Thus, our study establishes a regulatory cascade for UBP14/DA3-CDKB1;1-CDKG2/SUD6-mediated control of endoreduplication and cell growth in Arabidopsis.
Trichomes are specialized epidermal structures that protect plants from biotic and abiotic stresses by synthesizing, storing, and secreting defensive compounds. This study investigates the role of ...the Gossypium arboreum DNA topoisomerase VI subunit B gene (GaTOP6B) in trichome development and branching. Sequence alignment revealed a high similarity between GaTOP6B and AtTOP6B, suggesting a conserved function in trichome regulation. Although AtTOP6B acts as a positive regulator of trichome development, functional analyses showed contrasting effects: Virus-induced gene silencing (VIGS) of GaTOP6B in cotton increased trichome density, while its overexpression in Arabidopsis decreased trichome density but enhanced branching. This demonstrates that GaTOP6B negatively regulates trichome number, indicating species-specific roles in trichome initiation and branching between cotton and Arabidopsis. Overexpression of the GaTOP6B promotes jasmonic acid synthesis, which in turn inhibits the G1/S or G2/M transitions, stalling the cell cycle. On the other hand, it suppresses brassinolide synthesis and signaling while promoting cytokinin degradation, further inhibiting mitosis. These hormonal interactions facilitate the transition of cells from the mitotic cycle to the endoreduplication cycle. As the level of endoreduplication increases, trichomes develop an increased number of branches. These findings highlight GaTOP6B's critical role as a regulator of trichome development, providing new genetic targets for improving cotton varieties in terms of enhanced adaptability and resilience.
•GaTOP6B promotes the formation of trichome branches.•GaTOP6B accelerates the mitotic-to-endoreduplication transition.•GaTOP6B regulates the biosynthesis and signaling of JA, BR, and CK.
A contribution of DNA methylation to defense against invading nucleic acids and maintenance of genome integrity is uncontested; however, our understanding of the extent of involvement of this ...epigenetic mark in genome-wide gene regulation and plant developmental control is incomplete. Here, we knock out all five known DNA methyltransferases in Arabidopsis, generating DNA methylation-free plants. This quintuple mutant exhibits a suite of developmental defects, unequivocally demonstrating that DNA methylation is essential for multiple aspects of plant development. We show that CG methylation and non-CG methylation are required for a plethora of biological processes, including pavement cell shape, endoreduplication, cell death, flowering, trichome morphology, vasculature and meristem development, and root cell fate determination. Moreover, we find that DNA methylation has a strong dose-dependent effect on gene expression and repression of transposable elements. Taken together, our results demonstrate that DNA methylation is dispensable for Arabidopsis survival but essential for the proper regulation of multiple biological processes.
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