The G-protein regulatory (GPR) motif-containing Leu-Gly-Asn-enriched protein (LGN) and Giα3 influence cortical positioning of the mitotic spindle poles at metaphase in symmetrically dividing mammalian cells

We addressed the role of the G-protein regulatory (GPR) motif-containing Leu-Gly-Asn-enriched protein (LGN) and G-proteins (Gi alpha 3) in the positioning of the spindle pole during mammalian cell division. Immunocytochemistry indicated that both LGN and Gi alpha 3 co-localized at the spindle pole and at the midbody and the cell cortex during the different phases of mitosis. In marked contrast to the positioning of the spindle pole at metaphase midway between the cell cortex and the metaphase plate, the spindle pole was juxtaposed with the cell cortex at metaphase following increased expression of Gi alpha 3 and LGN. This repositioning of the spindle pole required the interaction of LGN with Gi alpha. The influence of LGN and Gi alpha 3 on the cortical positioning of the spindle pole likely reflects either stronger pulling forces on the spindle pole exerted from the cell cortex or increased pushing forces exerted on the spindle pole from the mitotic spindle indicating that these events are regulated by GPR motif-containing proteins and G-proteins independent of asymmetry. (c) 2006 Elsevier GmbH. All rights reserved.