“9.61x6.69” b2815 Tissue Engineering and Nanotheranostics
Directed Differentiation of Human Pluripotent Stem Cells 81
another marker, Nanog, was later established as a better method for
selection. iPSCs established through Fbx15 expression differ from
authentic ESCs in three ways: gene expression, DNA methylation pat-
terns, and failure to produce adult chimaeras. Nanog selected iPSCs
demonstrated competent generation of adult germ line chimaeras.^29
Yu et al. discovered another method to generate iPSCs using a dif-
ferent set of transcription factors: Oct3/4, Sox2, Nanog, and LIN28.
These iPSCs could be derived from human somatic cells such as human
foreskin and lung fibroblasts. The resulting cells met all of the same
pluripotency qualifications as those iPSCs created by Takahashi et al.
Since the introduction of iPSC technology, whenever reporting
new pluripotent maintenance or differentiation techniques for hESCs,
the study is often repeated on iPSCs as well. If results are successful
for hESC application, then similar results are expected with iPSCs.
3. Differentiation
Upon loss of signals promoting the undifferentiated state, a stem cell
will make the transition from pluripotency to a more specialized cell
type (neuron, beta cell, cardiomyocyte, etc.). This transition is called
differentiation and results in the formation of tissue from one to the
three germ layers: ectoderm, mesoderm, and endoderm. The activity
of different cellular signaling mechanisms aids in the determination of
which germ layer a cell will become. These signaling pathways regulate
gene transcription to create a unique pattern of gene expression cor-
responding to a cell’s fate. During differentiation, stem cells undergo
gradual shifts in morphology and function passing through several
intermediate stages before reaching a final specialized cell state.
In the embryo, differentiation begins in the blastula phase, where
the embryo takes the shape of a hollow ball. The blastula begins a
process called gastrulation, transitioning into three distinct germ lay-
ers. Gastrulation begins with an invagination of the hollow blastula
leading to the designation of the two earliest germ layers, ectoderm
and endoderm, followed by emergence of the mesoderm. Upon germ
layer specification, cells differentiation into final somatic cell types.
In recent years, biomedical science and regenerative medicine coor-
dinate synergistic efforts in technology development towards clinical
