The model of this current study showed that

The model of this current study showed that CD133 and CD24 markers, as a single or combined expression, are so promiscuous that they are not able to identify a pure population of adult renal stem cells. In PKHhigh cells, the only cell population presenting self-renew and an in vitro multipotency capacity, it was possible to identify three subpopulations with different phenotypes and behaviors on the basis of CD133 and CD24 expression. The CD133+/CD24−/PKHhigh phenotype identified the only pyrilamine maleate exhibiting self-renewal and multipotency for all three lineages analyzed. The CD133+/CD24+/PKHhigh phenotype had only a bipotent capacity although self-renewal is still maintained. This behavior looks like the one of the bipotent mammary progenitors which have clonogenic capacity (Zhao et al., 2012), even though it decreases through each passage (Dontu et al., 2003). The CD133−/CD24−/PKHhigh phenotype differentiated only as epithelium or endothelium and lost the self-renewal capacity, probably because of the lack of CD133, as described for adult renal progenitor cells (Sallustio et al., 2013) and for cancer stem cells (Lan et al., 2013; Li, 2013). Therefore the combination of PKHhigh status and CD133+/CD24− expression identify a stem population, never described before, that the in vitro assays suggest having self-renewal and multipotency capacity toward proximal and distal tubular, podocytic, and endothelial lineages. This cell population which gathered about 72% of the total PKHhigh cells, according to the calculated SFE of PKHhigh cells (about 72%), might be a candidate adult resident renal stem cell population. The PKHhigh status probably hides a molecular profile that, until now, has not been disclosed. Further studies are needed to better characterize these cells, and a wide-range expression profiling is needed to find a specific signature able to identify them and their localization and fate on renal tissue. In conclusion, the clonal nephrospheres described provided a homogeneous resident renal stem cell population more precisely defined with respect to those obtained using surface markers (Bussolati et al., 2005; Sagrinati et al., 2006), and permitted to isolate it with purity. It may represent a useful tool to better understand both the mechanisms that regulate self-renewal and differentiation in the adult renal tissues as well as the mechanisms that may be altered in nephropathies or renal cancer. The following are the supplementary data related to this article.
Conflict of interest statement
Acknowledgments We thank M.P. Rastaldi and E. Dugnani for useful advice; M Quinn for editing revision. This research was supported by MIUR Grants (PRIN, FAR) and in part by Associazione Gianluca Strada Onlus. The funders had no role in the study design and preparation of the manuscript. S.B. was a recipient of a Postdoctoral Fellowship and M.A.Z. of a PhD fellowship from MIUR; V.D.S was a recipient of a Postdoctoral Fellowship from Regione Lombardia–Fondazione Cariplo grant.
Introduction Multipotent horizontal basal cells (HBCs) differentiate into olfactory sensory neurons during normal neuronal turnover as well as during tissue regeneration after injury (Carter et al., 2004; Goldstein et al., 1998; Huard et al., 1998; Iwai et al., 2008; Lindsay et al., 2010). Several extracellular matrix proteins and growth factors control neuronal differentiation of HBCs (Carter et al., 2004; Gokoffski et al., 2011; Newman et al., 2000). Wnt signaling and transcription factor p63 are involved in HBC self-renewal (Wang et al., 2011; Fletcher et al., 2011; Packard et al., 2011). The majority of adult HBCs are derived from neural crest cells (Katoh et al., 2011; Suzuki et al., 2013). Schwann cells, sensory and autonomic neurons of the peripheral nervous system arise from the neural crest as well (Binder et al., 2011). Oligodendrocyte progenitor cells (OPCs) exist in the central nervous system (CNS). OPCs differentiate into oligodendrocytes in response to injury and demyelination. Although OPCs are multipotent, their fate remains controversial (Nishiyama et al., 2009). OPCs in the CNS express NG2 and platelet-derived growth factor receptor α (PDGFRα) (Nishiyama et al., 1996; Pringle et al., 1992) and generate oligodendrocytes and Schwann cells in induced demyelinated lesions (Zawadzka et al., 2010).