biostudies-literatureWolff IDNIGMS NIH HHSar71https://www.ebi.ac.uk/biostudies/studies/S-EPMC9635285biostudies-literatureUnknown33(8)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 <i>Caenorhabditis elegans</i> oocytes<i>,</i> 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.Molecular biology of the cellAcentrosomal spindle assembly and maintenance in <i>Caenorhabditis elegans</i> oocytes requires a kinesin-12 nonmotor microtubule interaction domain.PMC9635285T32 GM008382R01 GM124354Wignall SMWolff IDHollis JAfalseAcentrosomal spindle assembly and maintenance in <i>Caenorhabditis elegans</i> oocytes requires a kinesin-12 nonmotor microtubule interaction domain.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 <i>Caenorhabditis elegans</i> oocytes<i>,</i> 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.2022-01-01T00:00:00Z2022 Jul2025-04-05T12:34:03.965Z2025-04-05T12:34:03.965ZS-EPMC96352853559418210.1091/mbc.E22-05-0153