Stem cells have the unique ability to differentiate into many different cell types and play an important role in tissue regeneration and repair. There are several types of stem cells including embryonic stem cells, which are the most pluripotent and can differentiate into any fetal or adult cell. Adult stem cells are found in various tissues and can differentiate into a narrower range of cell types to replenish or repair that tissue. Induced pluripotent stem cells are generated in a lab by reprogramming adult cells using growth factors to return them to an undifferentiated state similar to embryonic stem cells. Stem cells offer promise for regenerative medicine and treatment of various diseases.

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Instituto de Pesquisa com Células-tronco (IPCT)
Federal University of Rio Grande do Sul (UFRGS)
Divulga Ciência Project, 2021™.
Stem Cells
Where it all starts
___
Course offered by IPCT with the Universidade Federal do Rio Grande do Sul
(UFRGS).
Copyright free imagem.
Summary
In this chapter we will see:
● What is a stem cell;
● How stem cells differentiate into somatic cells;
● Possible stem cell origins;
● Different stem cell types.

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Introduction
Cells are the most basic unit of life. They are composed of membranes, proteins, ions,
and many other biological structures and molecules. In an organism, there are different cell
types, which specialize in a variety of functions, forming the many types of tissue with their
morphological and physiological characteristics.
It can be said that the most known groups of cells are the animal and plant eukaryotic
cells (Figure 1). The major differences between these types being the cell wall and chloroplast,
present only in plant cell structures.
Figure 1. Animal and vegetal composition simplification, starting from a cell.

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Stem cells and their origins
The primary origin of Embryonic Stem Cells (ESCs) is found in the embryo, in the early
stages of development, where only a few cells with almost unlimited differentiation capability
exist; these are referred to as the ESCs. But what is the exact meaning of “differentiation
capability”?
The specialization or differentiation process (Figure 2) consists of a morphological and
physiological change in the SCs so they are able to execute the function of a desired somatic cell.
Different SCs types or lineages have different differentiation capabilities, and this is how a
complex body developing from a single cell is made possible.
Figure 2. Process entitled differentiation in which generic stem cells (left) become other specialized cell types, such as skin, blood, muscle, and brain
cells (right).

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Adult Stem Cell and Induced Pluripotent Stem Cell (iPS)
ASCs are also a type of non-differentiated cell capable of differentiating into a group of
somatic cells from a specific lineage. These cells come from different origins, as different tissue
types and states of development. As an example, some stem cells can be found in an early stage
of the organism’s life, like the embryonic SCs; others, from the bone marrow; or even the dental
tissue, as is the case for lineages derived from teeth.
It is also possible to generate SCs in a lab by a process of production of induced
pluripotent somatic cells, currently called induced pluripotent stem cells (iPS). Using different
bioactive molecules - like transcriptions and growth factors- we induce a somatic cell to express
a genetic pattern of a SC (Figure 3).
Figure 3. Somatic cells receiving treatment to return to the undifferentiation state, called induced pluripotent stem cells or iPS.

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Stem Cell types
SCs have different tissue origins in the organism and their differentiation capability varies
greatly. The most capable cells, considering the number of somatic types they can turn into, are
those found in the early stages of development. In this period, cells tend to have the capability of
differentiating into almost any somatic cell present in the body. Another group of SCs are the
adult ones; these can be found in almost all tissue types, and their differentiation capability is
reduced. The main function of this group is to renew degraded cells and repair tissue damage;
mesenchymal and hematopoietic are examples of cell types from this group.
When studying SCs, it is possible to see terms such as pluripotent or multipotent; this
classification is based on the differentiation capacity of the SCs. The main types are:
Totipotent: stem cells capable of originating almost all types of cells in the organism,
including embryonic attachments.
Pluripotent: stem cells capable of originating cells from all 3 embryonic layers, ectoderm,
mesoderm and endoderm.
Multipotent: stem cells with more limited differentiation capacity, usually only in regard
to the type of tissue in which they reside; hematopoietic stem cells are an example.

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References
BRAUN, A. C., PRANKE, P. Potencialidades da terapia com células-tronco na regeneração hepática. Rev. Inst. Adolfo Lutz,
65(3), 2006. Disponível em
<http://periodicos.ses.sp.bvs.br/scielo.php?script=sci_arttext&pid=S0073-98552006000300001&lng=pt&nrm=iso>. Acesso em
02 jun. 2021.
ZAKRZEWSKI, W., DOBRZYŃSKI, M., SZYMONOWICZ, M., RYBAK, Z. Stem cells: past, present, and future. Stem Cell
Res. Ther., 10(1), 2019. https://doi.org/10.1186/s13287-019-1165-5
BYDLOWSKI, S. P., DEBES, A. A., MASELLI, L. M. F., JANZ, F. L. Características biológicas das células-tronco
mesenquimais. Rev. Bras. Hematol. Hemoter., 31, 25–35, 2009. https://doi.org/10.1590/s1516-84842009005000038
ALMEIDA, P. N., CUNHA, K. S. Dental stem cells and their application in Dentistry: a literature review. Rev. Bras. Odontol.,
73 (4), 331-335, 2016. ISSN 1984-3747.
ANDRZEJEWSKA A., LUKOMSKA B., JANOWSKI M. Concise Review: Mesenchymal Stem Cells: From Roots to Boost.
Stem Cells.37(7), 855-864, 2019. https://doi.org/10.1002/stem.3016