Journal
JOURNAL OF CELL BIOLOGY
Volume 164, Issue 5, Pages 729-738Publisher
ROCKEFELLER UNIV PRESS
DOI: 10.1083/jcb.200309162
Keywords
epithelium; cell polarity; heterotrimeric G protein; spindle orientation; Drosophila melanogaster
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Drosophila melanogaster neuroblasts (NBs) undergo asymmetric divisions during which cell-fate determinants localize asymmetrically, mitotic spindles orient along the apical-basal axis, and unequal-sized daughter cells appear. We identified here the first Drosophila mutant in the Ggamma1 subunit of heterotrimeric G protein, which produces Ggamma1 lacking its membrane anchor site and exhibits phenotypes identical to those of Gbeta13F, including abnormal spindle asymmetry and spindle orientation in NB divisions. This mutant fails to bind Gbeta13F to the membrane, indicating an essential role of cortical Ggamma1-Gbeta13F signaling in asymmetric divisions. In Cgamma1 and Cbeta13F mutant NBs, Pins-God, which normally localize in the apical cortex, no longer distribute asymmetrically. However, the other apical components, Bazooka-atypical PKC-Par6-inscuteable, still remain polarized and responsible for asymmetric Miranda localization, suggesting their dominant role in localizing cell-fate determinants. Further analysis of Gbetagamma and other mutants indicates a predominant role of Partner of Inscuteable-Galphai in spindle orientation. We thus suggest that the two apical signaling pathways have overlapping but different roles in asymmetric NB division.
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