Chromosomes that have undergone crossing over in meiotic prophase must maintain sister chromatid cohesion somewhere along their length between the first and second meiotic divisions. To accomplish this, the holocentric organism Caenorhabditis elegans creates two chromosome domains of unequal length termed the short arm and long arm, which become the first and second site of cohesion loss at meiosis I and II. The mechanisms that confer distinct functions to the short and long arm domains remain poorly understood. Previously we and others have shown that phosphorylation of SYP-1, a central element of the synaptonemal complex (SC), at Thr452 provides a binding site for a Polo-like kinase PLK-2, and phosphorylated SYP-1 and PLK-2 cooperatively localize to the short arm to guide downstream factors triggering cohesin degradation at the short arm (Sato-Carlton et al. 2017; Brandt et al. 2020). Previous studies have shown that Polo kinase is activated via phosphorylation of its activation loop by Aurora kinase, and this interaction is promoted by Bora/SPAT-1 in mitosis (Tavernier et al. 2015). To understand the mode of Polo-like kinase regulation during meiotic prophase, we examined the effect of
spat-1 knockdown during oogenesis. We found that PLK-2 failed to spread to short arms but instead was confined at crossover designation sites in
spat-1 RNAi gonads. In addition, we found that homologous chromosome synapsis and crossover formation are impaired in
spat-1 RNAi animals. Interestingly, excess crossover designation, ranging from 6 to 13 sites per nucleus, was found in
spat-1 RNAi animals. Computational tracing of three-dimensional chromosome images revealed the presence of multiple crossover designation sites on the same chromosome, suggesting that crossover interference is impaired. These observations are reminiscent of
plk-2 mutant phenotypes, and suggest the possibility that SPAT-1 regulates PLK-2 during meiotic prophase. Brandt J. N., K. A. Hussey, and Y. Kim, 2020 Spatial and temporal control of targeting Polo-like kinase during meiotic prophase. J. Cell Biol. 219 Sato-Carlton A, Nakamura-Tabuchi C, Chartrand SK, Uchino T, Carlton PM (2018) Phosphorylation of the synaptonemal complex protein SYP-1 promotes meiotic chromosome segregation. J Cell Biol 217:555-570 Tavernier N., A. Noatynska, C. Panbianco, L. Martino, L. Van Hove, et al., 2015 Cdk1 phosphorylates SPAT-1/Bora to trigger PLK-1 activation and drive mitotic entry in C. elegans embryos. J. Cell Biol. 208: 661-669.