In Vitro Differentiation of Embryonic Stem Cells into Hepatocytes

Troika of the mouse blastocyst: lineage segregation and stem cells

The initial period of mammalian embryonic development is primarily devoted to cell commitment to the pluripotent lineage, as well as to the formation of extraembryonic tissues essential for embryo survival in utero. This phase of development is also characterized by extensive morphological transitions. Cells within the preimplantation embryo exhibit extraordinary cell plasticity and adaptation in response to experimental manipulation, highlighting the use of a regulative developmental strategy rather than a predetermined one resulting from the non-uniform distribution of maternal information in the cytoplasm. Consequently, early mammalian development represents a useful model to study how the three primary cell lineages; the epiblast, primitive endoderm (also referred to as the hypoblast) and trophoblast, emerge from a totipotent single cell, the zygote. In this review, we will discuss how the isolation and genetic manipulation of murine stem cells representing each of these three lineages has contributed to our understanding of the molecular basis of early developmental events.

Directing hepatic differentiation of embryonic stem cells with protein microarray-based co-cultures

Embryonic stem cells hold considerable promise in tissue engineering and regenerative medicine as a source of tissue-specific cells. However, realizing this promise requires novel methods for guiding lineage-specific differentiation of stem cells. In this study, we developed a micropatterned co-culture platform for stimulating hepatic differentiation of mouse embryonic stem cells (mESCs). Studies of mESC and hepatic cell adhesion preferences revealed that mESCs required fibronectin for attachment, while hepatic cells (HepG2) preferred collagen (I) substrate and did not adhere to fibronectin. Printing columns of collagen (I) and fibronectin spots (300 microm diameter), followed by sequential seeding of the two cell types, allowed the positioning of clusters of mESCs adjacent to groups of hepatic cells within the same microarray. These micropatterned co-cultures were maintained for up to two weeks in hepatic differentiation media supplemented. To examine the differentiation, mESCs were selectively extracted from the co-culture using laser microdissection and analyzed using real-time reverse transcriptase (RT)-polymerase chain reaction (PCR). These analyses revealed that mESCs co-cultured with HepG2 cells showed a decrease in pluripotency gene expression concomitant with up-regulation of endodermal genes. In addition, the co-culture format induced a significant increase in the expression of liver genes compared to mESCs cultured alone. In conclusion, micropatterned co-cultures of mESCs and hepatic cells showed a significant promise in driving stem cell differentiation towards hepatic phenotype. In the future, this cell culture platform will be further enhanced to enable efficient conversion of mouse and human ESCs to hepatocytes.

Role of mesenchymal stem cells in regenerative medicine: application to bone and cartilage repair

BACKGROUND

Mesenchymal stem cells (MSC) are multipotent cells with the ability to differentiate into mesenchyme-derived cells including osteoblasts and chondrocytes.

OBJECTIVE

To provide an overview and expert opinion on the in vivo ability of MSC to home into tissues, their regenerative properties and potential applications for cell-based therapies to treat bone and cartilage disorders.

METHODS

Data sources including the PubMed database, abstract booklets and conference proceedings were searched for publications pertinent to MSC and their properties with emphasis on the in vivo studies and clinical use in cartilage and bone regeneration and repair. The search included the most current information possible.

CONCLUSION

MSC can migrate to injured tissues and some of their reparative properties are mediated by paracrine mechanisms including their immunomodulatory actions. MSC possess a critical potential in regenerative medicine for the treatment of skeletal diseases, such as osteoarthritis or fracture healing failure, where treatments are partially effective or palliative.

Microfabrication-based modulation of embryonic stem cell differentiation

Embryonic stem (ES) cells form spontaneous aggregates during differentiation, and cell-cell communication in the aggregates plays an important role in differentiation. The development of a controlled differentiation scheme for ES cells has been hindered by the lack of a reliable method to produce uniform aggregate sizes. Conventional techniques, such as hanging drop and suspension cultures, do not allow precise control over size of ES cell aggregates. To surmount this problem, we microfabricated adhesive stencils to make mouse ES (mES) cell aggregates of specific sizes ranging from 100 microm to 500 microm in diameter. With this technique, we studied the effect of the initial aggregate size on ES cell differentiation. After 20 days of induction of differentiation, we analyzed the stem cell populations using gene and protein expression assays as well as biochemical functions. Notably, we found that germ layer differentiation depends on the initial size of the ES cell aggregate. Among the ES cell aggregate sizes tested, the aggregates with 300 microm diameter showed similar differentiation profiles of three germ layers as embryoid bodies made using the "hanging drop" technique. The smaller (100 microm) aggregates showed the increased expression of ectodermal markers compared to the larger (500 microm) aggregates, while the 500 microm aggregates showed the increased expression of mesodermal and endodermal markers compared to the 100 microm aggregates. These results indicate that the initial size of the aggregate is an important factor for ES cell differentiation, and can affect germ layer selection as well as the extent of differentiation.

Molecular control of liver development

Recent studies using animal models have elucidated a growing number of evolutionarily conserved genes and pathways that control liver development from the embryonic endoderm. It is increasingly clear that the genetic programs active in embryogenesis are often deregulated or reactivated in disease, cancer, and tissue repair. Understanding the molecular control of liver development should impact diagnosis and treatment of pediatric and adult liver diseases and aid in efforts to differentiate liver tissue in vitro for stem cell-based therapies.

Commitment of embryonic stem cells to an epidermal cell fate and differentiation in vitro

The epidermis develops from a stem cell population in the surface ectoderm that feeds a single vertical terminal differentiation pathway. To date, however, the limited capacity for the isolation or purification of epidermal stem or precursor cells has hampered studies on early commitment and differentiation events. We have developed a two-step culture scheme in which pluripotent mouse embryonic stem (ES) cells are induced first to a surface ectoderm phenotype and then are positively selected for putative epidermal stem cells. We show that the earliest stages of epidermal development follow an ordered sequence that is similar to that observed in vivo (expression of keratin 8, keratin 19, keratin 17, and keratin 14), suggesting that ES cell-derived surface ectoderm-like cells can be induced to follow the epidermal developmental pathway. At a low frequency, keratin 14-positive early epidermal cells progressed to keratin 1-positive and terminally differentiated cells producing a cornified envelope. This culturing protocol provides an invaluable system in which to study both the mechanisms that direct stem cells along the epidermal pathway as well as those that influence their subsequent epidermal differentiation.

Aggregation of embryonic stem cells induces Nanog repression and primitive endoderm differentiation

When embryonic stem cells are allowed to aggregate, the outer layer of the aggregated spheres (referred to as embryoid bodies) differentiates into primitive endoderm. This initial specification of cell lineage facilitates further differentiation of the inner mass of the embryoid bodies. These processes are considered to recapitulate early embryonic development from the blastocyst stage to the egg-cylinder stage. Formation of the primitive endoderm layer in the embryoid bodies was induced solely by aggregation of embryonic stem cells, in the presence of leukemia inhibitory factor/STAT3 and serum/BMP4, which were considered to be sufficient for embryonic stem cell self-renewal. Interestingly, cell aggregation by itself induced Nanog repression at the outer layer, which was essential for aggregation-induced primitive endoderm formation. These data illustrate aggregation-based cell-fate specification during early embryonic development, when downregulation of Nanog plays a crucial role.