The evolving biology of small molecules: controlling cell fate and identity

Small molecules have been playing important roles in elucidating basic biology and treatment of a vast number of diseases for nearly a century, making their use in the field of stem cell biology a comparatively recent phenomenon. Nonetheless, the power of biology-oriented chemical design and synthesis, coupled with significant advances in screening technology, has enabled the discovery of a growing number of small molecules that have improved our understanding of stem cell biology and allowed us to manipulate stem cells in unprecedented ways. This review focuses on recent small molecule studies of (i) the key pathways governing stem cell homeostasis, (ii) the pluripotent stem cell niche, (iii) the directed differentiation of stem cells, (iv) the biology of adult stem cells, and (v) somatic cell reprogramming. In a very short period of time, small molecules have defined a perhaps universally attainable naive ground state of pluripotency, and are facilitating the precise, rapid and efficient differentiation of stem cells into somatic cell populations relevant to the clinic. Finally, following the publication of numerous groundbreaking studies at a pace and consistency unusual for a young field, we are closer than ever to completely eliminating the need for genetic modification in reprogramming.     

A comment on the Hill–Turney exchange: from normative antagonism to interdisciplinary collaboration

Amniotic fluid-derived stem (AFS) cells were the first non-embryonic source of pluripotent stem cells discussed in Italy. AFS cells have been defined “ethical stem cells”, a socio-technical label denoting an array of cellular reprogramming techniques, biological artifacts, and somatic stem cells which make it possible to obtain pluripotent stem cells while avoiding the use of human embryos. The alleged pluripotent status of these cells triggered a debate in which pluripotency was re-positioned as the most promising feature of stem cells. This debate was characterized by discursive articulations in which the boundary between multipotency and pluripotency was blurred and a discourse on a duopoly of pluripotency (pertaining both to embryonic and non-embryonic stem cells) ensued. Drawing on qualitative discourse analysis of articles in scientific journals and newspapers, this paper explores the cultural meaning and political uses of these discursive articulations in the Italian stem cell research regulation debate. This paper also examines a set of aporias emerging from the attempt to incorporate ethical stances into the biological ontology of ethical stem cells, and the problem of constructing normativities in the biotechnology field.     

The use of signalling pathway inhibitors and chromatin modifiers for enhancing pluripotency

Pluripotent embryonic stem cells have been isolated from a limited number of species. The new advances with inducing pluripotency in somatic cells have resulted in the generation of pluripotent stem cells while circumventing the need for embryos. In this review we describe the main signalling pathways involved in maintaining pluripotency and inducing differentiation. Inhibition of the signalling pathways involved in differentiation enhances the derivation and cultivation of pluripotent stem cells. Furthermore, we discuss the use of chromatin modifiers to maintain an open chromatin state which is characteristic of pluripotent stem cells, to facilitate the derivation of pluripotent cell lines.     

Metabolic status of pluripotent cells and exploitation for growth in stirred suspension bioreactors

Pluripotent stem cells are of great interest in the field of regenerative medicine. Recent studies have shown that they maintain a glycolytic metabolic status while pluripotent and wholesale changes to mitochondrial and metabolic profile occur during differentiation. This article reviews the process and how this may be exploited in a stirred suspension bioreactor for rapid growth while maintaining pluripotency.     

Pluripotency in the embryo and in culture

Specific cells within the early mammalian embryo have the capacity to generate all somatic lineages plus the germline. This property of pluripotency is confined to the epiblast, a transient tissue that persists for only a few days. In vitro, however, pluripotency can be maintained indefinitely through derivation of stem cell lines. Pluripotent stem cells established from the newly formed epiblast are known as embryonic stem cells (ESCs), whereas those generated from later stages are called postimplantation epiblast stem cells (EpiSCs). These different classes of pluripotent stem cell have distinct culture requirements and gene expression programs, likely reflecting the dynamic development of the epiblast in the embryo. In this chapter we review current understanding of how the epiblast forms and relate this to the properties of derivative stem cells. We discuss whether ESCs and EpiSCs are true counterparts of different phases of epiblast development or are culture-generated phenomena. We also consider the proposition that early epiblast cells and ESCs may represent a naïve ground state without any prespecification of lineage choice, whereas later epiblasts and EpiSCs may be primed in favor of particular fates.     

Induced pluripotent stem cells derived from human amnion in chemically defined conditions

Fetal stem cells are a unique type of adult stem cells that have been suggested to be broadly multipotent with some features of pluripotency. Their clinical potential has been documented but their upgrade to full pluripotency could open up a wide range of cell-based therapies particularly suited for pediatric tissue engineering, longitudinal studies or disease modeling. Here we describe episomal reprogramming of mesenchymal stem cells from the human amnion to pluripotency (AM-iPSC) in chemically defined conditions. The AM-iPSC expressed markers of embryonic stem cells, readily formed teratomas with tissues of all three germ layers present and had a normal karyotype after around 40 passages in culture. We employed novel computational methods to determine the degree of pluripotency from microarray and RNA sequencing data in these novel lines alongside an iPSC and ESC control and found that all lines were deemed pluripotent, however, with variable scores. Differential expression analysis then identified several groups of genes that potentially regulate this variability in lines within the boundaries of pluripotency, including metallothionein proteins. By further studying this variability, characteristics relevant to cell-based therapies, like differentiation propensity, could be uncovered and predicted in the pluripotent stage.     

Lignin Induces ES Cells to Differentiate into Neuroectodermal Cells through Mediation of the Wnt Signaling Pathway

Embryonic stem cells (ES cells) are characterized by their pluripotency and infinite proliferation potential. Ever since ES cells were first established in 1981, there have been a growing number of studies aimed at clinical applications of ES cells. In recent years, various types of differentiation inducement systems using ES cells have been established. Further studies have been conducted to utilize differentiation inducement systems in the field of regenerative medicine. For cellular treatments using stem cells including ES cells, differentiation induction should be performed in a sufficient manner to obtain the intended cell lineages. Lignin is a high-molecular amorphous material that forms plants together with cellulose and hemicelluloses, in which phenylpropane fundamental units are complexly condensed. Lignin derivatives have been shown to have several bioactive functions. In spite of these findings, few studies have focused on the effects of lignin on stem cells. Our study aimed to develop a novel technology using lignin to effectively induce ES cells to differentiate into neuroectodermal cells including ocular cells and neural cells. Since lignin can be produced at a relatively low cost in large volumes, its utilization is expected for more convenient differentiation induction technologies and in the field of regenerative medicine in the future.