Multiple motors cooperate to establish and maintain acentrosomal spindle bipolarity in C. elegans oocyte meiosis

Abstract

While centrosomes organize spindle poles during mitosis, oocyte meiosis can occur in their absence. Spindles in human oocytes frequently fail to maintain bipolarity and consequently undergo chromosome segregation errors, making it important to understand mechanisms that promote acentrosomal spindle stability. To this end, we have optimized the auxin-inducible degron system in C. elegans to remove factors from pre-formed oocyte spindles within minutes and assess effects on spindle structure. This approach revealed that dynein is required to maintain the integrity of acentrosomal poles; removal of dynein from bipolar spindles caused pole splaying, and when coupled with a monopolar spindle induced by depletion of the kinesin-12 motor KLP-18, dynein depletion led to a complete dissolution of the monopole. Surprisingly, we went on to discover that following monopole disruption, individual chromosomes were able to reorganize local microtubules and re-establish a miniature bipolar spindle that mediated chromosome segregation. This revealed the existence of redundant microtubule sorting forces that are undetectable when KLP-18 and dynein are active. We found that the kinesin-5 family motor BMK-1 provides this force, uncovering the first evidence that kinesin-5 contributes to C. elegans meiotic spindle organization. Altogether, our studies have revealed how multiple motors are working synchronously to establish and maintain bipolarity in the absence of centrosomes.

Cannabis- and Substance-Related Epidemiological Patterns of Chromosomal Congenital Anomalies in Europe: Geospatiotemporal and Causal Inferential Study

“…It has recently been shown that Nuclear Mitotic Apparatus 1 (NUMA1) and the centrosomal proteins (CEP) CEP152 and CEP 55 are key to centrosomal function. The motor proteins kinesin and dynein-dynactin preform key role not only moving chromosomes but also on collecting the ends of microtubules together into cohesive mitotic spindle poles in a bipolar orientation [ 74 , 75 , 142 , 143 , 144 , 145 , 146 , 147 ]. Table 9 lists the EWAS hits identified in the Schrott datasets for some of these proteins.…”

“…However, as explored in some detail in the Discussion section, the exact mechanism of this is not understood in molecular terms. Perhaps the most likely explanations relate to disruptions of the post-translational modification code on either the tubulin which comprise the microtubules along which the chromosomes are pulled by cellular kinesin motors [ 74 , 75 , 76 ], the 90 proteins of the mammalian kinetochore which bind the chromosomes to the microtubules [ 77 ], or to the centrosomal chromatin itself [ 77 ]. Chromosomal scission and one or two whole genome doubling events [ 78 ] are also described as part of cannabinoid genotoxicity [ 79 ] all of which suggest gross disruption of the meiotic I machinery of spermatid division.…”

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

“…Our experiments demonstrated that an inward force exists, because the metaphase spindle rapidly shortened and then collapsed upon KLP-18 inhibition. Moreover, we recently found that dynein provides an inward force on the oocyte spindle, suggesting that it could antagonize KLP-18 ( Cavin-Meza et al. , 2022 ).…”

“…, 2017 ; Mullen and Wignall, 2017 ); because KLP-18 sorts microtubule minus ends outward during spindle assembly and is required for maintaining spindle length in metaphase, it is possible that it also exerts outward force to drive microtubule sliding during anaphase B. We recently found that when KLP-18 and dynein are both depleted, anaphase B can still occur ( Cavin-Meza et al. , 2022 ), demonstrating that this motor is not essential for outward sliding.…”

“…, 2016 ), whereas kinesin-5 (BMK-1) is not essential ( Bishop et al. , 2005 ); a role for BMK-1 in spindle assembly can be seen only under conditions where KLP-18 is depleted ( Cavin-Meza et al. , 2022 ).…”