3-D FINE STRUCTURE OF THE C ELEGANS MEIOTIC SPINDLE POLE

点击翻译按钮获取中文摘要

This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Faithful chromosome segregation during meiosis and mitosis depends on assembly of the microtubules (MTs) into a bipolar spindle. The meiotic spindle of the C. elegans ovum is morphologically distinct from the first mitotic spindle of the zygote, yet both structures form in the same cytoplasm approximately 20 minutes apart. Instead of nucleating from centrosomes as in mitosis, meiotic MTs polymerize initially around chromatin. Chromatin-associated plus-end directed motor proteins have been implicated in pushing MT minus ends away from the chromatin, and the MT array is then focused into two opposing poles. Recently the mei-1 and mei-2 genes of C. elegans were found to be required for meiotic spindle formation but not for mitotic spindle function. Genetic analysis has shown that mei-1 and mei-2 genes are the katanin orthologues in C. elegans. Katanin is a heterodimeric MT-severing protein consisting of a catalytic and a regulatory subunit. Loss-of-function mutations result in disorganized meiotic spindles and meiotic failure, but the subsequent mitotic spindles are normal. In contrast, gain-of-function mutations result in normal meiosis followed by mitosis on short spindles. These observations suggest that the MT severing activity of katanin may explain how meiotic spindles maintain their small size in a cytoplasm environment that later supports the assembly of a much larger mitotic spindle. We have produced serial tomograms from two female meiotic spindles and found that the majority (~80%) of the pole-proximal MT ends are open, in contrast to the closed/capped ends that predominate at the centrosome of the mitotic spindle. We are currently preparing strains with gain and loss-of-function mutations in mei-1 to determine how the 3D arrangements and morphology of MTs are affected by the function of katanin-like proteins during meiosis.