Multiple Wnts act synergistically to induce Chk1/Grapes expression and mediate G2 arrest in Drosophila tracheoblasts
Abstract
Larval tracheae of Drosophila harbor progenitors of the adult tracheal system (tracheoblasts). We showed previously that thoracic tracheoblasts arrest in the G2 phase of the cell cycle in an ATR-Checkpoint Kinase1(Chk1)-dependent manner prior to division and morphogenesis (Kizhedathu et al., 2018). Here we investigate developmental regulation of Chk1 activation. We report that Wnt signaling is high in tracheoblasts and is necessary for high levels of activated (phosphorylated) Chk1. We find that canonical Wnt signaling facilitates this by transcriptional upregulation of Chk1 in cells that have ATR kinase activity. Wnt signalling is dependent on four Wnts (Wg, Wnt5, 6,10) that are expressed at high levels in arrested tracheoblasts and downregulated at mitotic re-entry. Interestingly, none of the Wnts are dispensable and act synergistically to induce Chk1. Finally, we show that downregulation of Wnt signalling and Chk1 expression leads to mitotic re-entry and the concomitant upregulation of Dpp signalling, driving tracheoblast proliferation.
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All data generated or analysed during this study are included in the manuscript.
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Author details
Funding
Department of Biotechnology , Ministry of Science and Technology (inStem Core Grant)
- Arjun Guha
Department of Biotechnology , Ministry of Science and Technology (InStem Core Grant)
- Arjun Guha
The funders had no role in study design, data collection and interpretation, or the decision to submit the work for publication.
Reviewing Editor
- Amin S. Ghabrial, Columbia University, United States
Version history
- Received: March 20, 2020
- Accepted: August 29, 2020
- Accepted Manuscript published: September 2, 2020 (version 1)
- Accepted Manuscript updated: September 9, 2020 (version 2)
- Version of Record published: September 21, 2020 (version 3)
- Version of Record updated: September 24, 2020 (version 4)
Copyright
© 2020, Kizhedathu et al.
This article is distributed under the terms of the Creative Commons Attribution License permitting unrestricted use and redistribution provided that the original author and source are credited.
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Further reading
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- Developmental Biology
Imaginal progenitors in Drosophila are known to arrest in G2 during larval stages and proliferate thereafter. Here we investigate the mechanism and implications of G2 arrest in progenitors of the adult thoracic tracheal epithelium (tracheoblasts). We report that tracheoblasts pause in G2 for ~48–56 h and grow in size over this period. Surprisingly, tracheoblasts arrested in G2 express drivers of G2-M like Cdc25/String (Stg). We find that mechanisms that prevent G2-M are also in place in this interval. Tracheoblasts activate Checkpoint Kinase 1/Grapes (Chk1/Grp) in an ATR/mei-41-dependent manner. Loss of ATR/Chk1 led to precocious mitotic entry ~24–32 h earlier. These divisions were apparently normal as there was no evidence of increased DNA damage or cell death. However, induction of precocious mitoses impaired growth of tracheoblasts and the tracheae they comprise. We propose that ATR/Chk1 negatively regulate G2-M in developing tracheoblasts and that G2 arrest facilitates cellular and hypertrophic organ growth.
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- Cell Biology
- Chromosomes and Gene Expression
Heat stress is a major threat to global crop production, and understanding its impact on plant fertility is crucial for developing climate-resilient crops. Despite the known negative effects of heat stress on plant reproduction, the underlying molecular mechanisms remain poorly understood. Here, we investigated the impact of elevated temperature on centromere structure and chromosome segregation during meiosis in Arabidopsis thaliana. Consistent with previous studies, heat stress leads to a decline in fertility and micronuclei formation in pollen mother cells. Our results reveal that elevated temperature causes a decrease in the amount of centromeric histone and the kinetochore protein BMF1 at meiotic centromeres with increasing temperature. Furthermore, we show that heat stress increases the duration of meiotic divisions and prolongs the activity of the spindle assembly checkpoint during meiosis I, indicating an impaired efficiency of the kinetochore attachments to spindle microtubules. Our analysis of mutants with reduced levels of centromeric histone suggests that weakened centromeres sensitize plants to elevated temperature, resulting in meiotic defects and reduced fertility even at moderate temperatures. These results indicate that the structure and functionality of meiotic centromeres in Arabidopsis are highly sensitive to heat stress, and suggest that centromeres and kinetochores may represent a critical bottleneck in plant adaptation to increasing temperatures.