Arabidopsis MZT1 homologs GIP1 and GIP2 are essential for centromere architecture

Abstract

Centromeres play a pivotal role in maintaining genome integrity by facilitating the recruitment of kinetochore and sister-chromatid cohesion proteins, both required for correct chromosome segregation. Centromeres are epigenetically specified by the presence of the histone H3 variant (CENH3). In this study, we investigate the role of the highly conserved γ-tubulin complex protein 3-interacting proteins (GIPs) in Arabidopsis centromere regulation. We show that GIPs form a complex with CENH3 in cycling cells. GIP depletion in the gip1gip2 knockdown mutant leads to a decreased CENH3 level at centromeres, despite a higher level of Mis18BP1/KNL2 present at both centromeric and ectopic sites. We thus postulate that GIPs are required to ensure CENH3 deposition and/or maintenance at centromeres. In addition, the recruitment at the centromere of other proteins such as the CENP-C kinetochore component and the cohesin subunit SMC3 is impaired in gip1gip2. These defects in centromere architecture result in aneuploidy due to severely altered centromeric cohesion. Altogether, we ascribe a central function to GIPs for the proper recruitment and/or stabilization of centromeric proteins essential in the specification of the centromere identity, as well as for centromeric cohesion in somatic cells.centromere assembly | centromeric cohesion | ploidy stability | Arabidopsis | MZT1

MGO3 and GIP1 act synergistically for the maintenance of centromeric cohesion

“…Previously, we showed the involvement of both GIP1 and GIP2 at the nuclear interface 7 and herein, the contribution of GIP1 together with MGO3 to the maintenance of centromeric cohesion. MGO3/BRU1/TSK plays a role in stalling replication forks 12 as described for its homolog in humans, Tonsoku-Like (TONSL), 21,22 acting as a reader of new epigenetic marks linked to new histone incorporation at the post-replicative state.…”

“…A similarly increased number of pAL signals was observed for the less affected gip1gip2 type1 mutants. 7 These data argue for a synergistic contribution of MGO3 and GIP1 to centromeric cohesion. In addition, we observed an irregular distribution of pAL signals in the nuclei of both gip1mgo3 type a (8.6%; n D 93) and b (22%; n D 77) mutants compared with WT (Fig.…”

“…2B). 7 For a more accurate description of the centromere defect, we evaluated the number of centromeric signals in 4C flow sorted nuclei, using the FISH centromere-specific pAL probe. While in WT the number of pAL signals did not exceed 10, we observed more than 10 signals in 6 to 7% of the nuclei in the gip1 and mgo3 mutants as well as in the gip1mgo3 type a mutants (Fig.…”

“…5,6 GIPs located on both sides of the Nuclear Envelope (NE) play a critical role in the maintenance of centromeric cohesion in the nuclei of cycling cells studied in Arabidopsis root meristems. 7,8 Interestingly, GIPs were identified as partners of TSA1 6 which was first described as TONSOKU (TSK)-associating protein1. 9 TONSOKU (TSK) is specifically expressed during S phase.…”

Chromatin and epigenetics in all their states: Meeting report of the first conference on Epigenetic and Chromatin Regulation of Plant Traits - January 14 – 15, 2016 - Strasbourg, France

“…Related to this, MarieEdith Chaboute (IBMP, Strasbourg, France) presented a poster about the functional characterization of the newly found g-tubulin associated proteins GCP3-INTERACTING PROTEIN 1 and 2 (GIP1 and GIP2), which colocalized with the centromere-specific H3 variant CENH3 and contributed to the regulation of centromere at the interface between the nuclear envelope and the nucleoplasm. 4,5 While this was a conference for plant epigenetics, several invited speakers gave us the opportunity to expose our minds to other organisms. Wendy Bickmore (Institute of Genetics and Molecular Medicine, Edinburgh) discussed the relationships between structure and function in human cell nuclei, with the crucial issue of whether and to what extent the nuclear organization can directly affect gene function rather than merely reflecting it.…”