Slender lobes is a spindle matrix protein regulated by spindle envelope kinase Greatwall in oocytes

Chromosome segregation is mediated by microtubule-based machinery, the spindle. Microtubule-independent structures, often called the spindle matrix or the spindle envelope, have been reported to embed or surround the spindle, respectively. The concepts have been around for several decades, but they still remain enigmatic. Here, we show the spindle matrix and the spindle envelope form one functional unit crucial for spindle structure and function in oocytes. We found that in Drosophila oocytes, Slender lobes (Sle) protein is an integral component of the spindle matrix, which has a composition different from that in mitotic cells. We further found that Greatwall (Gwl) kinase localizes to the spindle envelope tightly surrounding the Sle spindle matrix in oocytes. Gwl promotes assembly of the Sle spindle matrix, which in turn determines the location of the Gwl spindle envelope. sle silencing in oocytes resulted in spindle abnormalities. Cosilencing experiments revealed that Sle buffers the impacts of compromised kinetochore-microtubule interaction on centromere bi-orientation in meiotic metaphase I.