Below is a collection of time-lapse videos illustrating the process of asymmetric cell division in Drosophila sensory organ precursor (SOP) cells. SOP cells are one of the best characterized model systems for asymmetric cell division as they generate the four different cell types constituting Drosophila external sensory organs in a stereotyped lineage. See the following reviews for further information:
Knoblich, J.A. (2008). Mechanisms of asymmetric stem cell division. Cell 132, 583-597.
Neumuller, R.A., and Knoblich, J. A. (2009). Dividing cellular asymmetry: asymmetric cell division and its implications for stem cells and cancer. Genes Dev 23, 2675-2699.
Knoblich, J.A. (2010). Asymmetric cell division: recent developments and their implications for tumour biology. Nat Rev Mol Cell Biol 11, 849-860.
Homem, C.C.F., and Knoblich, J.A. (2012). Drosophila neuroblasts: a model for stem cell biology. Development 139, 4297-4310.
In all movies, a fusion between Histone-2A and RFP labels DNA.
A high-magnification movie of a single dividing SOP cell highlights the dynamics of cell fate determinants during asymmetric cell division. Prior to mitosis GFP::Pon is localized uniformly in the cytoplasm. As the cell enters mitosis, however, it is increasingly recruited to the cell cortex. By nuclear envelope breakdown GFP::Pon becomes restricted to the anterior side of the cortex where it forms an intense crescent by metaphase. The alignment of the mitotic spindle with this axis of polarity ensures that cell fate determinants are segregated into only one daughter cell.
SOP cells are arranged in a regular array on the notum of a fly pupa. A GFP fusion with Partner-of-Numb (Pon) reveals the asymmetric segregation of cell fate determinants during the division of these cells. The area in between SOP cells is taken up by epithelial cells, which do not express any fluorescent marker. All SOP cells divide along the anterior-posterior axis of the pupa. Cell fate determinants, marked by GFP::Pon, are segregated into the anterior daughter cell where they make that cell different from its posterior sibling.
A GFP fusion with the mitotic kinase Aurora-A labels centrosomes during the division of an SOP cell. As the cell enters mitosis the centrosomes mature, which is reflected by increasing recruitment of GFP::Aurora-A. At prophase the centrosomes migrate to opposite sides of the nucleus to become the poles of the newly forming mitotic spindle.
A GFP fusion with Spaghetti squash (Sqh), a regulatory light chain of non-muscle myosin-II, reveals cortical dynamics during cell division. As the SOP cell enters mitosis Sqh::GFP is recruited into patches all around the cell cortex until, from prometaphase onwards, its cortical distribution becomes uniform. At anaphase Sqh::GFP is abruptly re-distributed to the site of the cleavage furrow. Here, myosin-II and actin form a contractile ring, which powers the physical separation of the daughter cells.
During mitosis SOP cells break down and re-establish certain aspects of their apical-basal polarity, as illustrated by this 3D reconstruction of a dividing SOP cell expressing a GFP fusion with sec15, a component of the exocyst complex. Prior to mitosis GFP::sec15 labels puncta (presumably vesicles), which gather beneath the apical cell membrane. At entry into mitosis these puncta are dispersed into the cytoplasm. Shortly after division, they re-appear near the centrosomes in both daughter cells. As the apical domain of the cell is re-established GFP::sec15 is swiftly transported back to the apical side of the cell.