Microtubule-severing activity of the AAA+ ATPase Katanin is essential for female meiotic spindle assembly

Abstract

In most animals, female meiotic spindles are assembled in the absence of centrosomes. How microtubules (MTs) are organized into acentrosomal meiotic spindles is poorly understood. In Caenorhabditis elegans, assembly of female meiotic spindles requires MEI-1 and MEI-2, which constitute the microtubule-severing AAA+ ATPase Katanin. However, the role of MEI-2 is not known and whether MT severing is required for meiotic spindle assembly is unclear. Here, we show that the essential role of MEI-2 is to confer MT binding to Katanin, which in turn stimulates the ATPase activity of MEI-1, leading to MT severing. To test directly the contribution of MT severing to meiotic spindle assembly, we engineered Katanin variants that retained MT binding and MT bundling activities but that were inactive for MT severing. In vivo analysis of these variants showed disorganized microtubules that lacked focused spindle poles reminiscent of the Katanin loss-of-function phenotype, demonstrating that the MT-severing activity is essential for meiotic spindle assembly in C. elegans. Overall, our results reveal the essential role of MEI-2 and provide the first direct evidence supporting an essential role of MT severing in meiotic spindle assembly in C. elegans.

KTN80 confers precision to microtubule severing by specific targeting of katanin complexes in plant cells

“…This in vitro work, together with our in vivo experiments, suggests that the preferred substrate of katanin complexes are sites where MTs interact with other MTs. Our findings are also consistent with an in vitro study showing a 1:1 stoichiometry MEI‐1:MEI‐2 within the katanin complex, which was suggested to be a hexamer of MEI‐1/MEI‐2 heterodimers (Joly et al , ). Based on the physical interaction between the N‐terminal microtubule interacting and trafficking domain of p60 and the C‐terminus of p80, the crystal structure of the mouse p60N/p80C heterodimer was recently resolved, providing the structural basis for formation of the p60/p80 heterodimer (Jiang et al , ).…”

Spindle assembly in egg extracts of the Marsabit clawed frog, Xenopus borealis

“…These findings support the idea that katanin and TPX2 are important spindle length control and assembly factors in Xenopus . Katanin‐mediated microtubule severing activity has been shown to regulate spindle size in several organisms, including Caenorhabditis elegans , Xenopus , and human cells (Jiang et al, ; Joly, Martino, Gigant, Dumont, & Pintard, ; Loughlin et al, ; McNally, Audhya, Oegema, & McNally, ), which is consistent with results from meiotic spindle assembly simulations showing that altering microtubule depolymerization rates robustly scales spindle length (Loughlin et al, ).…”

KATANIN 1 Is Essential for Embryogenesis and Seed Formation in Arabidopsis

“…Although the role of KATANIN 1 in the male and female gametogenesis is emerging in animal systems (O’Donnell et al, 2012; Joly et al, 2016; Tang et al, 2016) such function has not yet been found in plants. Future detailed genetic studies might eventually shed more light on gametophytic defects in the KATANIN 1 mutants.…”

“…In animal systems recent studies have shed light into the role of katanin severing complex during the female meiotic spindle assemby (Joly et al, 2016) in Caenorhabditis elegans and during sperm production in mouse (O’Donnell et al, 2012). Additionally, katanin complex severing microtubules is under tight regulation during the transition form the meiotic to mitotic stage to allow proper embryogenesis, as its persistence could have detrimental effects (Beard et al, 2016).…”