Self-renewal

In this Journal club, Meritxell Huch recalls a dogma postulated by Hayflick in 1961, that the capacity for propagating primary epithelial cells with normal ploidy is limited — a theory that persisted until the advent of organoid cultures.

Planaria are a group of worms within the phylum Platyhelminthes (flatworms). Many species, including Schmidtea mediterranea, have the ability to regenerate their body from small pieces of tissue and are easy to keep in the laboratory, which makes them a prime model system for studying whole-body regeneration.

Haematopoietic stem cells (HSCs) are maintained in vivo by intrinsic programs and extrinsic niche signals. Ex vivo expansion of HSCs is limited, owing to reduced stem cell maintenance factors. A study now shows that rejuvenated niche cells can be obtained by transcriptional rewiring of specific genes that maintain and expand HSCs ex vivo.

The cancer-suppressive mechanisms underlying a tissue’s response to spontaneous oncogenic mutations during homeostasis are largely unknown. A study now explores how clonal expansion of epidermal stem cells with specific oncogenic mutations might be restricted by their elimination through enforced differentiation.