Hexameric NuMA:LGN structures promote multivalent interactions required for planar epithelial divisions

Laura Pirovano,Chiara Gaddoni,Simone Culurgioni,Valentina Cecatiello,Silvia Monzani,Manuel Carminati,Andrea Alfieri,Francesca Rizzelli,Sebastiano Pasqualato,Marina Mapelli,James Foadi

doi:10.1038/s41467-019-09999-w

Abstract

Cortical force generators connect epithelial polarity sites with astral microtubules, allowing dynein movement to orient the mitotic spindle as astral microtubules depolymerize. Complexes of the LGN and NuMA proteins, fundamental components of force generators, are recruited to the cortex by Gαi-subunits of heterotrimeric G-proteins. They associate with dynein/dynactin and activate the motor activity pulling on astral microtubules. The architecture of cortical force generators is unknown. Here we report the crystal structure of NuMA:LGN hetero-hexamers, and unveil their role in promoting the assembly of active cortical dynein/dynactin motors that are required in orchestrating oriented divisions in polarized cells. Our work elucidates the basis for the structural organization of essential spindle orientation motors.

Highlights

Cortical force generators connect epithelial polarity sites with astral microtubules, allowing dynein movement to orient the mitotic spindle as astral microtubules depolymerize
Size-exclusion chromatography (SEC) elution profiles of LGN1–409 (LGNTPR in the following) bound to NuMA1900–1928 were consistent with a 1:1 binary interaction, in agreement with the available structural data[19] (Fig. 1a, b)
Spatial organization of traction forces pulling on astral microtubules to orient the spindle is achieved by recruitment of cytoplasmic dynein/dynactin at the cortex

Summary

Introduction

Cortical force generators connect epithelial polarity sites with astral microtubules, allowing dynein movement to orient the mitotic spindle as astral microtubules depolymerize. Complexes of the LGN and NuMA proteins, fundamental components of force generators, are recruited to the cortex by Gαi-subunits of heterotrimeric G-proteins They associate with dynein/dynactin and activate the motor activity pulling on astral microtubules. 1500-residue long coiled-coil mediating self-assembly, and an unstructured C-terminal portion harboring bindings sites for microtubules[9,10,11], lipids[12,13], importin-α14, the cortical protein 4.1R15,16, and the spindle orientation protein LGN17,18 (Supplementary Fig. 1). Depolymerization of astral MTs by low doses of nocodazole does not affect the cortical localization of NuMA in metaphase (unpublished data) in spite of causing spindle misorientation[8] These observations suggest that NuMA is not transported to the cortex along astral MTs by kinesins, but rather acts upstream of the microtubule motors in the assembly of cortical force generating complexes.

Methods

Results

Conclusion