Fig. 4.

Asymmetric cell division as a mechanism for removing cellular damage. In budding yeast, extrachromosomal DNA, carbonylated proteins and damaged organelles are sequestered in the mother cell, allowing the daughter cell to inherit more ‘youthful’ components in a process requiring the SIR2 deacetylase (a homolog of the mammalian sirtuins). During divisions of mammalian stem cells, similar processes maintain a ‘youthful’ state, in this case in the stem cell. Such polarized divisions, which require the activity of CDC42, become less frequent with increasing age.