Two types of asymmetric divisions in the Drosophila sensory organ precursor cell lineage

Abstract

Asymmetric partitioning of cell-fate determinants during development requires coordinating the positioning of these determinants with orientation of the mitotic spindle. In the Drosophila peripheral nervous system, sensory organ progenitor cells (SOPs) undergo several rounds of division to produce five cells that give rise to a complete sensory organ. Here we have observed the asymmetric divisions that give rise to these cells in the developing pupae using green fluorescent protein fusion proteins. We find that spindle orientation and determinant localization are tightly coordinated at each division. Furthermore, we find that two types of asymmetric divisions exist within the sensory organ precursor cell lineage: the anterior-posterior pI cell-type division, where the spindle remains symmetric throughout mitosis, and the strikingly neuroblast-like apical-basal division of the pIIb cell, where the spindle exhibits a strong asymmetry at anaphase. In both these divisions, the spindle reorientates to position itself perpendicular to the region of the cortex containing the determinant. On the basis of these observations, we propose that two distinct mechanisms for controlling asymmetric cell divisions occur within the same lineage in the developing peripheral nervous system in Drosophila.

PAR3 acts as a molecular organizer to define the apical domain of chick neuroepithelial cells

“…Furthermore, the asymmetric localization of Numb during SOP division is controlled by BAZ (Bellaiche et al, 2001;Roegiers et al, 2001), with the LGL protein being also involved in this process (Langevin et al, 2005). Given the defects in LGL1 distribution caused by cPAR3 overexpression, we asked whether cPAR3 also controls cNumb localization in NEP cells.…”

“…The LGL protein can interact directly with PAR6 and this might result in its inactivation by aPKCmediated phosphorylation (Betschinger et al, 2003;Yamanaka et al, 2003). Furthermore, LGL controls the asymmetric localization of Numb during divisions of neural precursors in Drosophila (Ohshiro et al, 2000;Peng et al, 2000;Langevin et al, 2005), in a process where PAR3 seems to also play a crucial role (Bellaiche et al, 2001; Roegiers et al, 2001). …”

Molecular pathways regulating mitotic spindle orientation in animal cells

“…cell polarity (PCP) within the imaginal disc tissue. The spindle must be controlled in both an A-B orientation, through the action of the Pins complex, as well as an A-P orientation, which is controlled by a non-canonical Frizzled/Dishevelled (Fz/Dsh) signaling pathway (David et al, 2005;Gho and Schweisguth, 1998;Roegiers et al, 2001) (Fig. 1C).…”

Cell polarity

“…49,50 The Wnt pathway as a regulator of cell division or cell movement has also been proposed in neurite extension as well as in the division of neuroblasts in Drosophila and vulval precursor cells in C. elegans. 51,52 In some asymmetric cell divisions, activation of Frizzled receptors and the intracellular signaling molecule Dishevelled by Wnt ligands localizes a complex of Pins/LGN, Mud/NUMA and the G protein Gα i , among others, to orient the mitotic spindle. 53,54 However, it is not yet established whether Wnt5a activates this pathway to regulate the presumed symmetric divisions during limb development.…”