Tissue-Resident Adult Stem Cell Populations of Rapidly Self-Renewing Organs

Abstract

The epithelial lining of the intestine, stomach, and skin is continuously exposed to environmental assault, imposing a requirement for regular self-renewal. Resident adult stem cell populations drive this renewal, and much effort has been invested in revealing their identity. Reliable adult stem cell biomarkers would accelerate our understanding of stem cell roles in tissue homeostasis and cancer. Membrane-expressed markers would also facilitate isolation of these adult stem cell populations for exploitation of their regenerative potential. Here, we review recent advances in adult stem cell biology, highlighting the promise and pitfalls of the candidate biomarkers of the various stem cell populations.

Pituitary Stem Cells: Quest for Hidden Functions

“…Taken together, the findings from lineage tracing do not support a major input of stem cells in adult pituitary homeostatic turnover, which is in line with findings in other 'lazy' tissues (Barker et al 2010;Huch et al 2013a,b;Rando 2006;Slack 2008;Vankelecom 2012;Wabik and Jones 2015).…”

“…The tissue stem cells not only give rise to new specialized cells of the organ but must also perpetuate by producing at least one 'selfie.' Differentiation potential (ranging from uni-to multipotency) and selfrenewal capacity indeed represent the core hallmarks of adult tissue stem cells (Barker et al 2010;De Los Angeles et al 2015;Rando 2006;Wabik and Jones 2015). On the other hand, the degree of activity of adult stem cells is clearly dependent on the tissue.…”

“…Some organs show rapid cell turnover within days and contain highly energetic stem cells that drive this renewal (as, for instance, intestine and skin). Other organs are more static in their cell composition and only need cell replacement at a very low pace (such as the brain, heart, liver, pancreas, lung; Alvarez-Buylla and Lim 2004; Barker et al 2010;Huch et al 2013a,b;Rando 2006;Slack 2008;Vankelecom 2012;Wabik and Jones 2015). The pituitary belongs to the latter group, undergoing turnover in terms of months rather than days (Levy 2002(Levy , 2008Nolan et al 1998;Rando 2006;Vankelecom 2012;Vankelecom and Chen 2014).…”

“…Compared to the expanding molecular stripping of the pituitary stem cell phenotype, functional characterization of the cells clearly lags behind. In general, stem cells in 'lazy' low-turnover tissues are highly quiescent, and activation only clearly emerges in conditions of disease or damage (Barker et al 2010;Huch et al 2013a,b;Rando 2006;Slack 2008;Vankelecom 2012;Vankelecom and Chen 2014;Wabik and Jones 2015). Regarding the yet hidden functions of the pituitary stem cells, recent studies have shed some light on this obscure domain, particularly in the context of early postnatal maturation, damage repair and tumor growth.…”

Identification of Lineage-Uncommitted, Long-Lived, Label-Retaining Cells in Healthy Human Esophagus and Stomach, and in Metaplastic Esophagus

“…The lack of bone fide gastroesophageal stem cell markers has made it difficult to conclude absolutely that LRCs are stem cells. Antibodies to LGR5 are currently unreliable and lineage tracing from a single lgr5 stem cell has only been demonstrated in the murine pylorus 38 . Antibodies to musashi-1 have been shown to bind to parietal cells 39,40 and no lineage tracing from a musashi-1-positve cell has been published and studies using CD133 have only shown lineage tracing in the intestine not the upper gastrointestinal tract 41 .…”