The GTPase Gem and its partner Kif9 are required for chromosome alignment, spindle length control, and mitotic progression

Abstract

Within the Ras superfamily, Gem is a small GTP-binding protein that plays a role in regulating Ca(2+) channels and cytoskeletal remodeling in interphase cells. Here, we report for the first time that Gem is a spindle-associated protein and is required for proper mitotic progression. Functionally, loss of Gem leads to misaligned chromosomes and prometaphase delay. On the basis of different experimental approaches, we demonstrate that loss of Gem by RNA interference induces spindle elongation, while its enforced expression results in spindle shortening. The spindle length phenotype is generated through deregulation of spindle dynamics on Gem depletion and requires the expression of its downstream effector, the kinesin Kif9. Loss of Kif9 induces spindle abnormalities similar to those observed when Gem expression is repressed by siRNA. We further identify Kif9 as a new regulator of spindle dynamics. Kif9 depletion increases the steady-state levels of spindle α-tubulin by increasing the rate of microtubule polymerization. Overall, this study demonstrates a novel mechanism by which Gem contributes to the mitotic progression by maintaining correct spindle length through the kinesin Kif9.

Acquired expression of CblQ367P in mice induces dysplastic myelopoiesis mimicking chronic myelomonocytic leukemia

“…GEM belongs to the Ras superfamily of small GTPases that are involved in various intracellular pathways. [33][34][35] Studies have demonstrated that GEM contributes to cell invasion, 36 mitotic progression, 37 and actin remodeling. 38 In addition, GEM has been reported to be an adverse prognostic factor in patients with bladder carcinoma 39 and upregulated in mutant ALK-expressing neuroblastoma cells.…”

High expression of GEM and EDNRA is associated with metastasis and poor outcome in patients with advanced bladder cancer

“…GEM is a small GTP-binding protein that plays a role in regulating Ca 2+ channel expression at the cell surface [30]. Furthermore, it is involved in cytoskeletal remodeling in interphase cells and is a spindle-associated protein required for prober mitotic progression [31]. EDNRA is a G-protein coupled receptor for endothelins and it is expressed on vascular smooth-muscle cells and on heart, kidney, and neuronal cells [32].…”

A role for KIF9 in male fertility

“…These tissues can contain primary cilia, however, and the low levels of KIF9 could reflect a potential function in primary cilia. In addition, KIF9 has been reported to be important for matrix degradation in macrophages [1] as well as interacting with GEM with possible functions in spindle control [2,17]. The low levels of signal detected in tissues that do not have multiciliated cells may reflect such alternative functions.…”

“…A pair of gRNAs targeting intron 2 (gRNAE22) and intron 3 (gRNAE23) of KIF9 gene respectively were designed using an online tool (https://benchling.com/) and generated by in vitro transcription [1] (Table 1 and Figure 1). Cas9 protein was purchased from PNA Bio Inc. A KIF9 conditional knockout(CKO) HRD plasmid carrying around 2kb homologous arms on each side surrounding a floxed KIF9 exon3 with an added primer sequence (KS) for genotyping (Supplementary Data 1) was generated by SLiCE cloning [2]. Superovulated female C57BL6 mice (3-4 weeks old) were mated to C57BL6 males, and fertilized embryos were collected from oviducts.…”

“…In mammalian cells, the kinesin family member 9, KIF9, has been reported to contribute to the ability of macrophages to degrade extracellular matrix [1], potentially through the regulation of delivery of matrix degrading enzymes to the cell surface. In addition, suppression of KIF9 expression has been reported to have effects on spindle dynamics [2]. Intriguingly, KIF9 is overexpressed in glioblastoma and correlates with poor outcome in that disease [3].…”