A stem cell can divide for indefinite periods - often throughout life. Under specific conditions or given specific signals, stem cells can give rise (differentiate) to many different cell types such as skin cells, heart cells, nerve cells, etc. Based on the origin and the pluripotency state, stem cells can be divided into embryonic stem cells and adult stem cells which include mesenchymal stem cells, hematopoietic stem cells, and neural stem cells, etc. SABiosciences provides different stem cells and developmental pathways focused PCR arrays. To learn more about stem cell and
development, click here.
Stem cells have two properties: pluripotency - the ability to differentiate
into nearly all cells of the three germ layers (ectoderm, endoderm, and
mesoderm), and self-renewal - the ability of going through numerous cycles of
cell division while maintaining its undifferentiated state. Stem cells typically
generate an intermediate cell type before progressing to their fully
differentiated state. The intermediate cell is called a precursor or progenitor
cell. Progenitor or precursor cells in fetal or adult tissues are partially
differentiated and usually regarded as "committed" to differentiating
into a particular cell lineage. Stem cells can be categorized into two general
groups: embryonic stem cells (ESCs) and adult stem cells.
Embryonic stem cells (ESCs) are derived from the blastocyst stage (approximately
4 to 5 days old in humans and consisting of 50-150 cells) of the embryo. A
fertilized egg first divides (cleavage stage), forms a ball of cells (morula
stage), then develops a cavity (blastocyst stage), forms the three germ layers -
(endoderm, mesoderm, and ectoderm) - that make up the gastrula stage, and
ultimately generates all the specialized tissues and organs of a mature
organism. ESC lacks the G1 checkpoint in the cell cycle and spends most of the
time in the S phase of the cell cycle. The X chromosome is not inactivated in
ESC.
Stem cells are also found in adult tissues. They can generate cell types other
than the one from which they normally derive. This feature is called stem cell
plasticity. Adult stem cells have been derived from brain, bone marrow,
peripheral blood, dental pulp, spinal cord, blood vessels, skeletal muscle,
cornea, retina, liver, pancreas, epithelia of the skin, and digestive system,
etc.
Mesenchyme is embryonic connective tissue derived from the mesoderm that later
differentiates into hematopoietic and connective tissue. Though mesenchymal stem
cells (MSC) can differentiate into osteoblast, chondrocytes, myocytes,
adipocytes, endothelial cells, and beta-pancreatic islet cells, they do not
differentiate into hematopoietic cells. There is no assay that can be performed
on a single cell to determine whether a cell is an MSC or not.
Hematopoietic stem cells (HSCs) can generate all the blood cell types and
sustain the blood system. Technically, it is hard to identify HSCs. HSCs can be
isolated based on a distinctive set of cell surface markers. However,
considerable debate exists whether some proposed cell populations are truly stem
cells. There are many other types of stem cells, such as endothelial, epithelial
and skeletal muscle stem cells. You can use SABiosciences' popular Stem Cell,
Mesenchymal Stem Cell, Neurogenesis and Neural Stem Cell, and Hematopoietic Stem
Cell PCR arrays to study stem cell gene expression.
Several populations of neural stem cells have been identified in the brain,
particularly in the hippocampus. Epidermal growth factor (EGF) and fibroblast
growth factor (FGF) are mitogens that promote neural progenitor and stem cell
growth in vitro.
Stem cell biology began a new era in 1998 with the derivation of cells from
human blastocysts and fetal tissue. Several research teams have characterized
many of the molecular characteristics of these cells and improved methods of
cell culture since then. Different sets of biomarkers have been used to identify
different types of stem cells. Human embryonic stem cells are defined by the
presence of several transcription factors and cell surface proteins. The
transcription factors Oct-4, Nanog, Sox2, and KLF4 ensure the maintenance of
pluripotency and the suppression of genes that lead to differentiation. The cell
surface proteins most commonly used to identify hESC are the glycolipids SSEA3
and SSEA4 and the keratan sulfates Tra-1-60 and Tra-1-81.
A surprising yet profound discovery opened up a new era for stem cell research -
terminally differentiated somatic cells can also be reprogrammed to generate
induced pluripotent stem (iPS) cells by overexpression of a combination of
transcription factors such as Oct3, Sox2, Klf4, and c-Myc or Oct3, Sox2, Nanog,
and Lin28.
Cell cycle, cell death, DNA methylation, and genomic imprinting all greatly
affect cell development and differentiation. The process of marking a gene as
being inherited from either the father or the mother is called genomic
imprinting. A common method of imprinting is DNA methylation. DNA methylation
patterns change during development, and their rearrangement in different tissues
at different times is an important method for controlling gene expression.
TGFbeta, Wnt, Notch, and Hedgehog signaling pathways are four fundamental
pathways involved in development. An important group of developmental control
genes - homeobox (HOX) genes and the proteins they encode - the homeodomain
proteins, were discovered in 1983. Homeobox genes control anterior-posterior
(front-back) orientation and the body segmentation. A homeobox domain is a
sequence of DNA of about 180 basepairs found in homeobox genes. The protein
domain encoded by the homeobox, the homeodomain, is about 60 amino acids long
and binds to DNA. The target genes of HOX genes promote cell division, cell
adhesion, apoptosis, and cell migration. HOX genes can be silenced by polycomb
proteins through modulation of chromatin structure.
Stem cell based therapies hold great promise for treating damaged brain or
spinal cord, autoimmune diseases (rheumatoid arthritis, type 1 diabetes,
multiple sclerosis, inflammatory bowel disease, lupus, etc.), cardiovascular
diseases, and cancer.
In addition to the Homeobox (HOX) Genes, Epigenetic Chromatin Modification
Enzymes and Epigenetic Chromatin Remodeling Factors, TGFbeta, Wnt, Notch and
Hedgehog Signaling Pathway - focused PCR arrays, SABiosciences also offers
unique Human Stem Cell Transcription Factors ChIP and Methylation PCR arrays.