NuMA-related LIN-5, ASPM-1, calmodulin and dynein promote meiotic spindle rotation independently of cortical LIN-5/GPR/Gα

Abstract

The spindle apparatus dictates the plane of cell cleavage, which is critical in the choice between symmetric or asymmetric division. Spindle positioning is controlled by an evolutionarily conserved pathway, which involves LIN-5/GPR-1/2/Galpha in Caenorhabditis elegans, Mud/Pins/Galpha in Drosophila and NuMA/LGN/Galpha in humans. GPR-1/2 and Galpha localize LIN-5 to the cell cortex, which engages dynein and controls the cleavage plane during early mitotic divisions in C. elegans. Here we identify ASPM-1 (abnormal spindle-like, microcephaly-associated) as a novel LIN-5 binding partner. ASPM-1, together with calmodulin (CMD-1), promotes meiotic spindle organization and the accumulation of LIN-5 at meiotic and mitotic spindle poles. Spindle rotation during maternal meiosis is independent of GPR-1/2 and Galpha, yet requires LIN-5, ASPM-1, CMD-1 and dynein. Our data support the existence of two distinct LIN-5 complexes that determine localized dynein function: LIN-5/GPR-1/2/Galpha at the cortex, and LIN-5/ASPM-1/CMD-1 at spindle poles. These functional interactions may be conserved in mammals, with implications for primary microcephaly.

Aspm sustains postnatal cerebellar neurogenesis and medulloblastoma growth

“…In Drosophila, asp maintains mitotic spindle orientation during both mitosis and meiosis (Zhong et al, 2005;van der Voet et al, 2009;Kaindl et al, 2010;Rujano et al, 2013). In mice, Aspm is required to maintain spindle organization and positioning and acts as a microtubule-organizing center in telencephalic neuroepithelial progenitors (Fish et al, 2006;Higgins et al, 2010).…”

Polarity Control of Spindle Positioning in the C. elegans Embryo

“…The proteins are present at the spindle poles, in the cytoplasm, at the cell cortex, and, specifically in metaphase, at kinetochore microtubules. GPR-1/GPR-2 fails to localize in the absence of LIN-5, and LIN-5 loses its cortical localization when GPR-1/GPR-2 or Gα is gone (Lorson et al 2000;Srinivasan et al 2003;van der Voet et al 2009). The combined data support that Gαi/o·GDP, GPR-1/GPR-2, and LIN-5 form a trimeric complex needed for spindle positioning in C. elegans (Fig.…”

“…The physical association between LIN-5 and GPR-1/GPR-2, as well as interaction between GPR-1/GPR-2 and Gα, and the strong resemblance in lin-5, gpr-1/gpr-2, and goa-1/gpa-16 RNAi phenotypes all supported a model in which the encoded proteins act together to control the mitotic spindle position. In addition, lin-5 is also required for meiotic spindle rotation, independently of gpr-1/gpr-2 and goa-1/gpa-16 Gα (Lorson et al 2000;van der Voet et al 2009). …”

“…Vice versa, par-3 mutant embryos are "posteriorized" with both sides showing high pulling forces (Grill et al 2001). The knockdown of Gα, gpr-1/gpr-2, or lin-5 largely eliminates these pulling forces (Nguyen-Ngoc et al 2007), while specific loss of LIN-5 from spindle poles has no effect (van der Voet et al 2009). Thus, cortical localization of LIN-5, through Gα-GPR-1/GPR-2 interaction, is needed for the pulling forces that position the spindle in mitosis.…”

“…In meiosis of the C. elegans female pronucleus, LIN-5 and dynein are needed to rotate the meiotic spindle in order to expel the polar bodies. Instead of Gα-GPR-1/GPR-2, a complex of ASPM-1 (abnormal spindle-like, microcephaly associated) and calmodulin anchors LIN-5 and dynein at the spindle poles to mediate this rotation (van der Voet et al 2009). In planar cell polarity, the Frizzled receptor and Dishevelled effector orient the spindle and division plane.…”