| In Drosophila, localization of maternal RNAs to the opposite poles of the oocyte is an essential step in establishing anterior-posterior polarity of the future embryo. The Drosophila Mini spindles (Msps) protein is a component of meiotic and mitotic spindles, and is required for both types of cell division. Given its role in regulating the integrity of microtubules during mitosis and meiosis and its maternal expression, we asked whether msps is also required for a process regulated by interphase microtubules, subcellular mRNA localization during oogenesis. We found that bicoid (bcd) mRNA localization is completely lost in embryos from msps mutant mothers, whereas oskar (osk) mRNA remains localized in msps embryos. Moreover, in msps mutant ovaries, GFP-Exu particles frequently appear to form large aggregates, fail to accumulate near ring canals, and are transported into the oocyte inefficiently. Intriguingly, we found that the microtubule density at the ring canals, within the nurse cells, and the anterior oocyte cortex decreases in msps mutants beginning at stage 9, when the level of Msps protein is also strongly reduced. Taken together, these results suggest that Msps plays crucial roles in Exu particle transport from the nurse cells to the oocyte, and a bcd anterior localization step in the oocyte that is initiated in mid-oogenesis.; We identified the aimless (aim) gene in a screen for maternal effect lethal mutations that cause mis-localization of polar mRNAs, including bcd and osk, and also cause early embryonic arrest associated with defects in mitotic spindle formation. We have cloned aim using a cosmid and transgene-rescue approach. Alternative splicing produces distinct isoforms different in their C-terminal zinc fingers. The Aim protein is a predicted transcription factor containing a BTB/POZ domain at its amino terminus and carboxyl terminal DNA binding CCHH-type zinc fingers. Consistent with its predicted structure, Aim is a nuclear protein expressed throughout oogenesis. We propose that Aim regulates the expression of genes that regulate MT structures and RNA localization pathway. |
