Figure 1.

Mechanisms of asymmetric stem cell division. (a) Asymmetric stem cell division can be regulated by extrinsic fate determinants, such as those from the stem cell niche. The two daughters of the stem cell division will be placed in distinct cellular environments, either inside or outside the stem cell niche, resulting in the acquisition of different fates. (b) Asymmetric stem cell division can be modulated by intricate mechanisms that reinforce initial cell-extrinsic and/or -intrinsic asymmetries. For example, stem cell division might be barely asymmetric (e.g. slight differences due to the age of mother and daughter centrosomes and due to only a moderate gradient in signaling molecules). However, the mother centrosome grows a primary cilium earlier than the daughter, and as a result, the mother centrosome-containing cell might receive much higher levels of signal, leading to asymmetric cell fates. (c) Asymmetric stem cell division may rely on intrinsic fate determinants. Fate determinants are polarized in the dividing stem cells, leading to unequal distribution of these determinants following division and to two daughter cells with distinct fates.