Acentrosomal spindle assembly and maintenance in Caenorhabditis elegans oocytes requires a kinesin-12 nonmotor microtubule interaction domain

• Published in: Molecular biology of the cell Vol. 33; no. 8; pp. 1 - ar71
• Main Authors: Wolff, Ian D, Hollis, Jeremy A, Wignall, Sarah M
• Format: Journal Article
• Language: English
• Published: American Society for Cell Biology 01.07.2022; The American Society for Cell Biology
• Subjects: Analysis; Caenorhabditis elegans; Centrosomes; Genetic aspects; Growth; Identification and classification; Kinesin; Microtubules; Oocytes; United States
• ISSN: 1059-1524; 1939-4586
• DOI: 10.1091/mbc.E22-05-0153

In Caenorhabditis elegans oocytes, kinesin-12/KLP-18 is the major force-generating motor that promotes spindle bipolarity. A combination of in vitro and in vivo approaches is used to gain insight into the mechanisms by which KLP-18 and its adaptor MESP-1 promote spindle assembly, and it is shown that KLP-18 is also continuously required to maintain bipolarity. During the meiotic divisions in oocytes, microtubules are sorted and organized by motor proteins to generate a bipolar spindle in the absence of centrosomes. In most organisms, kinesin-5 family members crosslink and slide microtubules to generate outward force that promotes acentrosomal spindle bipolarity. However, the mechanistic basis for how other kinesin families act on acentrosomal spindles has not been explored. We investigated this question in Caenorhabditis elegans oocytes , where kinesin-5 is not required to generate outward force and the kinesin-12 family motor KLP-18 instead performs this function. Here we use a combination of in vitro biochemical assays and in vivo mutant analysis to provide insight into the mechanism by which KLP-18 promotes acentrosomal spindle assembly. We identify a microtubule binding site on the C-terminal stalk of KLP-18 and demonstrate that a direct interaction between the KLP-18 stalk and its adaptor protein MESP-1 activates nonmotor microtubule binding. We also provide evidence that this C-terminal domain is required for KLP-18 activity during spindle assembly and show that KLP-18 is continuously required to maintain spindle bipolarity. This study thus provides new insight into the construction and maintenance of the oocyte acentrosomal spindle as well as into kinesin-12 mechanism and regulation.