Live imaging of stem cell and progeny behaviour in physiological hair-follicle regeneration

Abstract

Tissue development and regeneration depend on cell–cell interactions and signals that target stem cells and their immediate progeny1. However, the cellular behaviours that lead to a properly regenerated tissue are not well understood. Using a new, non-invasive, two-photon (intravital instead of two-photon?) imaging approach we study physiological hair-follicle regeneration in real time in live mice. By these means we have monitored the behaviour of epithelial stem cells and their progeny2–4 during physiological hair regeneration and addressed how the mesenchyme5 influences their behaviour. Consistent with earlier studies6, stem cells are quiescent during the initial stages of hair regeneration, whereas the progeny is more actively dividing. Moreover, stem cell progeny divisions are spatially organized within follicles. In addition to cell divisions, coordinated cell movements of the progeny allow the rapid expansion of the hair follicle. Finally, we show the requirement of the mesenchyme for hair regeneration through targeted cell ablation and long-term tracking of live hair follicles. Thus, we have established an in vivo approach that has led to the direct observation of cellular mechanisms of growth regulation within the hair follicle and that has enabled us to precisely investigate functional requirements of hair-follicle components during the process of physiological regeneration.

Responses of hair follicle–associated structures to loss of planar cell polarity signaling

“…Fourth, a large number of tissue stains, antibodies, and genetically directed cell marking methods have been developed for selectively visualizing a wide variety of skin structures. For completeness, we also note two additional experimental strengths arising from the surface location of skin that were not used in the present study: skin can be directly imaged in living animals and skin is highly amenable to experimental manipulation such as infection by transducing viruses to alter gene expression (31,32). Taken together, these attributes make mammalian skin a uniquely attractive tissue in which to study the interaction of macroscopic and microscopic patterning systems.…”

Dynamic stem cell heterogeneity

“…In recent years, pioneering studies using in vivo live-imaging platforms have begun to provide access to continuous-time lineage data (Bertrand et al, 2010;Boisset et al, 2010;Lam et al, 2010;Yaniv et al, 2006;Ritsma et al, 2013;Rompolas et al, 2012), whereas methods based on single-cell deep sequencing now offer the potential to resolve individual phylogenies, even in human tissues (Shapiro et al, 2013;Treutlein et al, 2014). By combining these lineage-tracing approaches with static marker-based assays, snapshots of clonal evolution over time can be integrated with population-level measures to reveal how stem and progenitor cells contribute to tissue maintenance.…”

“…Furthermore, progenitors expressing the same putative stem cell marker can exhibit heterogeneous fate choices (Graf and Stadtfeld, 2008), while stem cells with different expression profiles may behave similarly in the long term. Finally, recent studies in disparate tissues have also shown that cells normally committed to differentiation can, in the course of regeneration following the targeted ablation of endogenous stem cell populations, re-acquire the hallmark properties of tissue stem cells, including the potential for long-term self-renewal (Rompolas et al, 2012;van Es et al, 2012;Tata et al, 2013;Yanger et al, 2014;Tetteh et al, 2015).…”

Calcineurin/Nfatc1 signaling links skin stem cell quiescence to hormonal signaling during pregnancy and lactation

“…As cells in the HG proliferate to promote hair growth, bulge SCs divide to replenish the follicular SC pool (Zhang et al 2009). To regulate their activity, follicle cells receive signals from surrounding dermal cells, including those in the dermal papilla (DP), a mesenchymal compartment associated with the HF (Greco et al 2009;Rompolas et al 2012;Chi et al 2013); neurons (Brownell et al 2011); smooth muscle cells (Fujiwara et al 2011); Ó 2014 Goldstein et al This article is distributed exclusively by Cold Spring Harbor Laboratory Press for the first six months after the full-issue publication date (see http://genesdev.cshlp.org/site/misc/terms.xhtml). After six months, it is available under a Creative Commons License (Attribution-NonCommercial 4.0 International), as described at http:// creativecommons.org/licenses/by-nc/4.0/.…”