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Lecture 1, Part A: Developmental
Welcome to the course
Biology Review –
iPSCs
&
New
Technologies
Stem cells, Gene Expression & Cellular
Diversity
Dr. Sonya M. Schuh-Huerta
&
Dr. Shawn L. Chavez
References
The animal cell
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Golgi complex
Endoplasmic
reticulum (ER)
Mitochondrion
Nucleus
Plasma
membrane
(DNA inside)
Vacuole
Nuclear
membrane
1
References
The cell cycle and mitosis
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Mitosis (M)
The cell cycle
(parental cell)
Prophase
Mitosis (M)
Prometaphase
Interphase
Resting
phase
(daughter cells)
Metaphase
Telophase
Anaphase
DNA synthesis (S)
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All cell types in a multicellular organism
are generated from a single cell
[Image taken from Gilbert’s “Developmental Biology”, 8th edition, Sinauer].
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3
Multicellular organisms have a variety
of differentiated cell types
Immature
undifferentiated cells
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Mature differentiated cells
(~200 different cell types)
Stem cell
Heart muscle cells
(Cardiomyocytes)
Epidermal skin cells
Neurons
Red & white
blood cells
Progenitor cell
(S. Schuh-Huerta)
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Stem cells: what are they?
Stem cell
Differentiation
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1. Are Pluripotent – have the
potential to give rise to all
the cell types of the body
2. Can self renew – when
they divide, they give rise to
more stem cells
3. There are 2 main types of
stem cells – in the embryo
and in the adult
Neuron
Symmetric vs. asymmetric cell
division in stem cells
Symmetric
stem cell division
expansion
References
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Asymmetric
stem cell division
maintenance
Progenitor
Two stem cells
Stem cell
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Chromosomes, Genes and DNA
Nucleus
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1. The nucleus contains genetic material
in structures called chromosomes
Duplicated
chromosome
2. Chromosomes are long strands of
DNA wrapped around a protein core
3. DNA is made of 4 chemical bases:
A, T, C & G
Duplicated
chromosome
4. Sequences of chemical bases make up
genes
DNA
helix
5. Animals share common genes
6. Genes are the basic units of heredity
gene
7. Humans have ~25,000 genes
8. The entirety of DNA in a cell is an
organism’s genome
sister chromatids
7
The Central Dogma represents the
flow of genetic information
Transcription
DNA
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Translation
RNA
PROTEIN
Gene Expression
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Transcription: DNA makes RNA
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Transcription
DNA
RNA
RNA polymerase
Strand of DNA
Forming strand of mRNA
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Exception: DNA made from RNA
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Reverse Transcription
cDNA
mRNA
RNA-dependent
DNA polymerase
Strand of mRNA
Forming strand of cDNA
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Translation: RNA makes protein
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Translation
RNA
PROTEIN
Forming strand of amino acids:
Each group of 3 bases codes for
unique amino acid
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Proteins: the product of
translation
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• Hemoglobin (carries oxygen in blood)
• Insulin (regulates sugar breakdown/storage)
• Enzymes (catalyze biochemical reactions)
• Skin and hair color pigments
• Signaling molecules
– Allow cells to communicate
– Control cell division
– Coordinate development
– Help ward off infection
Protein Folding
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Summary of gene expression
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1. Begins with genes in the nucleus
2. Genes have a code consisting of A, T, C and G
3. The code is “transcribed” into RNA (a messenger)
4. Messenger RNA (mRNA) brings the code to the cytoplasm
5. The genetic code uses groups of three bases (ie. CCG, GUU) to
encode each amino acid of a protein chain
6. Amino acids are the building blocks of proteins (there are 22
amino acids)
7. Proteins are long chains of amino acids
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Various differentiated cell types
express different proteins
Cell type
Motor neuron
Heart muscle cell
(Cardiomyocyte)
References
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Red blood cells
Unique protein
Choline Acetyltransferase:
enzyme that produces the
chemical signal for neuronmuscle communication
Myosin Light Chain 2:
causes muscle
contraction
Hemoglobin:
transports oxygen from
lungs & carbon dioxide
from body
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Differential gene expression underlies the
presence of distinct proteins in various cells
Motor neuron
Heart muscle cell
(Cardiomyocyte)
References
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Red blood cells
Gene expression
OFF
OFF
ON
-globin gene
ON
OFF
OFF
ON
OFF
ChAT gene
OFF
Myosin light chain 2 gene
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Transcription factors regulate the flow
of genetic information
DNA
Transcription
RNA
Translation
References
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PROTEINS
Gene regulation
• Some proteins termed “transcription factors” regulate the flow
of genetic information.
• These are nuclear proteins capable of binding DNA.
• They regulate the process of gene transcription in immature and
differentiated cells.
• Transcription factors are essential for the processes of
development and stem cell maintenance.
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Signaling proteins are essential for
cell-to-cell communication
Secreted signaling molecules
References
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• Secreted proteins
• Form gradients when secreted
from cells
• Function by binding proteins
(receptors) at the surface of the
plasma membrane
• Activate intracellular proteins &
signaling transduction pathways
that relay information from the
surface to inside the cell
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Differential cell signaling contributes
to the generation of cellular diversity
References
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Cell signaling pathways
Shh
Patched/
Smoothened
Progenitor
cell
Activin/TGF
Erythropoietin
BMPRI
EPO receptor
Progenitor
cell
Progenitor
cell
Different signal transduction pathways activated
Motor neuron
Heart muscle cell
(Cardiomyocyte)
Red blood cells
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Differential gene expression underlies
the process of differentiation
References
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• Every nucleus contains a complete genome established in the
fertilized egg (with a few exceptions).
• The mouse genome contains tens of thousands of genes, and
the human genome about 25,000 genes, but many are not
expressed in all tissues.
• Many genes are differentially expressed in various tissues or
organs.
• Unused genes in differentiated cells are not destroyed or
mutated – they retain the potential to be expressed.
• Only a small percentage of the genome is expressed in each
cell.
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