| Summary: | 博士 === 國防醫學院 === 生命科學研究所 === 91 === The Drosophila compound eye is composed of about 800 ommatidia, which display planar polarity with the regular arrangement of these asymmetric ommatidia. Establishment of planar polarity in the Drosophila compound eye requires precise 90o rotation of the ommatidial clusters during development. Ommatidial clusters of dorsal and ventral compartments rotate in opposite direction, thus establishing opposite chirality across the dorsoventral midline. In addition to the signals from the equator and the dorsal and ventral poles of the developing eye discs, we found that the progressing morphogenetic furrow (MF) emits signals to control the stop of rotation at 90o. In the furrow-stop mutant hh1 and roDOM, the ommatidial clusters over-rotate. This over-rotation phenotype is caused by the disruption of MF progression, suggesting that the MF emits signals to control the stop of ommatidial rotation. One such signal, Scabrous (Sca), is synthesized in the furrow cells and transported in vesicles to posterior ommatidial clusters. Scabrous functions non-autonomously to control the stop of ommatidial rotation by suppressing nemo activity in the second 45° rotation.
Sca is transported posteriorly via actin-based cellular extensions of the MF cells, but not transcytosis. Further characterization of these cellular extensions revealed that they contain similar membrane composition to the plasma membrane. The extension of these cellular processes is independent on Sca itself. These cellular extensions protruded away from the high Dpp gradient and wriggled in ato1 clones at which no R cell formed, suggesting Dpp gradient in MF repels them posteriorly and their tension and organization is maintained by differentiated R cells. Transportation in these cellular extensions is regulated: except that Sca, GFP/Sca fusion proteins, and WgGFP are transported in vesicles, all tested secreted proteins and cytoplasmic GFP diffused in them; secreted HRP and wheat germ agglutinine (WGA) even could not be transported through them. Furthermore, Sca signal peptide alone is sufficient for this transportation. The cellular extension transports Sca vesicles to R6 cells by protruding basally and posteriorly from MF, which does not require the secretion of Sca/Sca vesicles. Therefore, we propose that the morphogenetic furrow regulates precise ommatidial rotation by transporting Sca and perhaps other factors through these cellular extensions; from the MF, Sca is transported basally and posteriorly to R6 precursors situated at the basal of disc proper to arrest cluster rotation at 90o through antagonizing nemo activity later.
|
|---|
