Asymmetric cell division results in two unequal daughter cells and without it, stem cells would not hold the attention of biologists, sick patients, politicians, and those loud nut-jobs who have more passion than knowledge. Check out today’s image, from a paper identifying a new protein complex important in asymmetric division.
Asymmetric division occurs throughout development, and is when a cell divides to result in two daughter cells that are unequal in size and/or cell fate. Part of this process is the establishment of the axis along which the cell will divide. Once this polarity is established, the mitotic spindle can line up accordingly. Fruit fly neural stem cells, called neuroblasts, divide asymmetrically to result in the birth of another neuroblast and a smaller ganglion mother cell, which eventually gives rise to neurons. A recent paper identifies a new role for a signaling complex in establishing neuroblast polarity. In this paper, Carmena and colleagues found that the Rap1–Rgl–Ral complex of proteins regulates polarity establishment in fruit fly neuroblasts, and works alongside other well-studied polarity proteins such as aPKC, Par6, and Pins. As seen in the images above, Rap1 (bottom row, green in merged; arrows) is enriched on only one side (apical side) of neuroblasts throughout division (DNA is in red).
Carmena, A., Makarova, A., & Speicher, S. (2011). The Rap1-Rgl-Ral signaling network regulates neuroblast cortical polarity and spindle orientation originally published in The Journal of Cell Biology, 195 (4), 553-562 DOI: 10.1083/jcb.201108112