Background: Generation of cell-fate diversity in Metazoan depends in part on asymmetric cell divisions in which cell-fate determinants are asymmetrically distributed in the mother cell and unequally partitioned between daughter cells. The polarization of the mother cell is a prerequisite to the unequal segregation of cell-fate determinants. In the Drosophila bristle lineage, two distinct mechanisms are known to define the axis of polarity of the pI and pIIb cells. Frizzled (Fz) signaling regulates the planar orientation of the pI division, while Inscuteable (Insc) directs the apical-basal polarity of the pIIb cell. The orientation of the asymmetric division of the pIIa cell is identical to the one of its mother cell, the pI cell, but, in contrast, is regulated by an unknown Insc- and Fz-independent mechanism.
Results: DE-Cadherin-Catenin complexes are shown to localize at the cell contact between the two cells born from the asymmetric division of the pI cell. The mitotic spindle of the dividing pIIa cell rotates to line up with asymmetrically localized DE-Cadherin-Catenin complexes. While a complete loss of DE-Cadherin function disrupts the apical-basal polarity of the epithelium, both a partial loss of DE-Cadherin function and expression of a dominant-negative form of DE-Cadherin affect the orientation of the pIIa division. Furthermore, expression of dominant-negative DE-Cadherin also affects the position of Partner of Inscuteable (Pins) and Bazooka, two asymmetrically localized proteins known to regulate cell polarity. These results show that asymmetrically distributed Cad regulates the orientation of asymmetric cell division.
Conclusions: We describe a novel mechanism involving a specialized Cad-containing cortical region by which a daughter cell divides with the same orientation as its mother cell.