Rooting the Stems

Stem cells are the ‘mothers’ that give rise to all the different cell types in our body, during development and throughout adult life. Despite growing knowledge of their function and behaviour, how stem cells themselves originate remains unclear. To address this question, researchers studied the hair follicles of mice, pictured above (in blue) at different stages of development, from simple clusters of cells, or placodes, to mature hair buds. Stem cell activity is typically maintained by signals from a group of nearby cells, known as the niche. Yet a different mechanism operates in hair buds, independently from a niche: when a placode cell divides, an asymmetrical distribution of certain molecules between daughter cells causes one to become a stem cell. The molecules involved, Wnt and SHH, are also implicated in skin cancers, so understanding their role in triggering stem cell activity is crucial.

Written by Emmanuelle Briolat

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Placodes (depicted above), like neural crest cells, are multipotent cells unique to vertebrates. Placodes are ectodermal in origin and can either be neurogenic or non-neurogenic. Neurogenic placodes give rise to nervous or sensory cranial structures. Non-neurogenic placodes, such as epidermal placodes, give rise to hair follicles, teeth, and feathers.

Photo Credit: Dr Mark Hill, UNSW Embryology