@article {2324, title = {Duox generated reactive oxygen species activate ATR/Chk1 to induce G2 arrest in tracheoblasts.}, journal = {Elife}, volume = {10}, year = {2021}, month = {2021 Oct 08}, abstract = {

Progenitors of the thoracic tracheal system of adult (tracheoblasts) arrest in G2 during larval life and rekindle a mitotic program subsequently. G2 arrest is dependent on ATR-dependent phosphorylation of Chk1 that is actuated in the absence of detectable DNA damage. We are interested in the mechanisms that activate ATR/Chk1 (Kizhedathu et al., 2018, 2020). Here we report that levels of reactive oxygen species (ROS) are high in arrested tracheoblasts and decrease upon mitotic re-entry. High ROS is dependent on expression of Duox, an HO generating-Dual Oxidase. ROS quenching by overexpression of Superoxide Dismutase 1, or by knockdown of Duox, abolishes Chk1 phosphorylation and results in precocious proliferation. Tracheae deficient in Duox, or deficient in both Duox and regulators of DNA damage-dependent ATR/Chk1 activation (ATRIP/TOPBP1/ Claspin), can induce phosphorylation of Chk1 in response to micromolar concentrations of HO in minutes. The findings presented reveal that HO activates ATR/Chk1 in tracheoblasts by a non-canonical, potentially direct, mechanism.

}, issn = {2050-084X}, doi = {10.7554/eLife.68636}, author = {Kizhedathu, Amrutha and Chhajed, Piyush and Yeramala, Lahari and Sain Basu, Deblina and Mukherjee, Tina and Vinothkumar, Kutti R and Guha, Arjun} } @article {2149, title = {Multiple Wnts act synergistically to induce Chk1/Grapes expression and mediate G2 arrest in tracheoblasts.}, journal = {Elife}, volume = {9}, year = {2020}, month = {2020 09 02}, abstract = {

Larval tracheae of harbour progenitors of the adult tracheal system (tracheoblasts). Thoracic tracheoblasts are arrested in the G2 phase of the cell cycle in an ATR (mei-41)-Checkpoint Kinase1 (grapes, Chk1) dependent manner prior to mitotic re-entry. Here we investigate developmental regulation of Chk1 activation. We report that Wnt signaling is high in tracheoblasts and this is necessary for high levels of activated (phosphorylated) Chk1. We find that canonical Wnt signaling facilitates this by transcriptional upregulation of Chk1 expression in cells that have ATR kinase activity. Wnt signaling is dependent on four Wnts (Wg, Wnt5, 6,10) that are expressed at high levels in arrested tracheoblasts and are 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 signaling and Chk1 expression leads to mitotic re-entry and the concomitant upregulation of Dpp signaling, driving tracheoblast proliferation.

}, issn = {2050-084X}, doi = {10.7554/eLife.57056}, author = {Kizhedathu, Amrutha and Kunnappallil, Rose Sebastian and Bagul, Archit V and Verma, Puja and Guha, Arjun} } @article {1150, title = {Negative regulation of G2-M by ATR (mei-41)/Chk1(Grapes) facilitates tracheoblast growth and tracheal hypertrophy in Drosophila.}, journal = {Elife}, volume = {7}, year = {2018}, month = {2018 Apr 16}, abstract = {

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.

}, issn = {2050-084X}, doi = {10.7554/eLife.29988}, author = {Kizhedathu, Amrutha and Bagul, Archit V and Guha, Arjun} }