title: Argonaute-1 functions as a mitotic regulator by controlling Cyclin B during Drosophila early embryogenesis.
abstract: The role of Ago-1 in microRNA (miRNA) biogenesis has been thoroughly studied, but little is known about its involvement in mitotic cell cycle progression. In this study, we established evidence of the regulatory role of Ago-1 in cell cycle control in association with the G2/M cyclin, cyclin B. Immunostaining of early embryos revealed that the maternal effect gene Ago-1 is essential for proper chromosome segregation, mitotic cell division, and spindle fiber assembly during early embryonic development. Ago-1 mutation resulted in the up-regulation of cyclin B-Cdk1 activity and down-regulation of p53, grp, mei-41, and wee1. The increased expression of cyclin B in Ago-1 mutants caused less stable microtubules and probably does not produce enough force to push the nuclei to the cortex, resulting in a decreased number of pole cells. The role of cyclin B in mitotic defects was further confirmed by suppressing the defects in the presence of one mutant copy of cyclin B. We identified involvement of 2 novel embryonic miRNAs--miR-981 and miR--317-for spatiotemporal regulation of cyclin B. In summary, our results demonstrate that the haploinsufficiency of maternal Ago-1 disrupts mitotic chromosome segregation and spindle fiber assembly via miRNA-guided control during early embryogenesis in Drosophila. The increased expression of cyclin B-Cdk1 and decreased activity of the Cdk1 inhibitor and cell cycle checkpoint proteins (mei-41 and grp) in Ago-1 mutant embryos allow the nuclei to enter into mitosis prematurely, even before completion of DNA replication. Thus, our results have established a novel role of Ago-1 as a regulator of the cell cycle.
authors.affiliation: 2Centre for Chemical Biology, Indian Institute of Chemical Technology, Uppal Road, Hyderabad 500607, India. manikapb@gmail.com.
authors.forename: Sreerangam N C V L
authors.initials: SN
authors.lastname: Pushpavalli
authors.forename: Arpita
authors.initials: A
authors.lastname: Sarkar
authors.forename: Indira
authors.initials: I
authors.lastname: Bag
authors.forename: Clayton R
authors.initials: CR
authors.lastname: Hunt
authors.forename: M Janaki
authors.initials: MJ
authors.lastname: Ramaiah
authors.forename: Tej K
authors.initials: TK
authors.lastname: Pandita
authors.forename: Utpal
authors.initials: U
authors.lastname: Bhadra
authors.forename: Manika
authors.initials: M
authors.lastname: Pal-Bhadra
mesh_terms: D000818:Animals; D060565:Argonaute Proteins / Q000235:genetics / Q000378:metabolism*; D002460:Cell Line; D000071877:Checkpoint Kinase 1; D019926:Cyclin B / Q000235:genetics / Q000378:metabolism*; D004330:Drosophila; D029721:Drosophila Proteins / Q000235:genetics / Q000378:metabolism*; D047108:Embryonic Development / Q000235:genetics / Q000502:physiology*; D007150:Immunohistochemistry; D035683:MicroRNAs / Q000235:genetics; D008938:Mitosis / Q000235:genetics / Q000502:physiology*; D060888:Real-Time Polymerase Chain Reaction
chemical_list: C489654:AGO1 protein, Drosophila; D060565:Argonaute Proteins; D019926:Cyclin B; D029721:Drosophila Proteins; D035683:MicroRNAs; D000071877:Checkpoint Kinase 1; C000605877:grp protein, Drosophila
keywords: Ago-1; cdk1; grp; miR-317; p53