1. Development, Stem Cells, and Cancer16
Development, Stem Cells, and Cancer

2. Concept 16.1: A program of differential gene expression leads to the different cell types in a multicellular organism
Transformation from zygote to adult results from cell division, cell differentiation, and morphogenesis
Cell differentiation - process by which cells become specialized in structure and function
Morphogenesis - the processes that give an organism its shape 2

3. (a) Fertilized eggs of a frog (b) Newly hatched tadpole
Figure 16.2
Figure 16.2 From fertilized egg to animal: What a difference four days makes.
1 mm
2 mm
(a) Fertilized eggs of a frog
(b) Newly hatched tadpole 3

4. Cytoplasic Determinants and Inductive Signals
Two factors that control cell differentiation include:
Cytoplasmic determinants: maternal substances (RNA and proteins-including transcription factors) encoded by the mother’s DNA) found in the cytoplasm of an unfertilized egg

5. Assist with gene expression regulation during cell differentiation (after fertilization)
Cytoplasmic determinants are distributed unequally in cytoplasm
The same determinants tend to stay together

7. 2nd Factor Influencing Cell Differentiation:
Induction - signal molecules from embryonic cells cause transcriptional changes in nearby target cells
Helps induce differentiation of many specialized cell types
Usually occurs later in embryonic development

9. (a) Cytoplasmic determinants in the egg (b) Induction by nearby cells
Figure 16.3
(a) Cytoplasmic determinants in the egg
(b) Induction by nearby cells
Unfertilized egg
Early embryo
(32 cells)
Sperm
Nucleus
Fertilization
Molecules of
two different
cytoplasmic
determinants
Zygote
(fertilized
egg)
NUCLEUS
Signal
transduction
pathway
Mitotic
cell division
Figure 16.3 Sources of developmental information for the early embryo
Signal
receptor
Two-celled
embryo
Signaling
molecule
(inducer) 9

10. Sequential Regulation of Gene Expression During Cellular Differentiation
Determination process that commits a cell irreversibly to its final fate
Determination precedes differentiation
If a cell has undergone determination, it will still differentiate into its expected cell type 10

11. In a fully differentiated cell, transcription is the primary regulatory point for maintaining gene expression
Become specialized at making tissue-specific proteins

12. Ex. Determination and Differentiation of a Muscle Cell
Signals from other cells lead to an activation of a master regulatory gene (myoD)
Makes a transcription factor that acts as an activator
Now committed to a muscle cell
Above process: determination

14. MyoD stimulates the regulatory gene further and activates other genes to produce other necessary transcription factors

15. Apoptosis: A Type of Programmed Cell Death
Apoptosis is the best-understood type of “programmed cell death”
Occurs in some cells during differentiation 15

16. Cells undergoing apoptosis
Figure 16.6
1 mm
Interdigital tissue
Cells undergoing apoptosis
Space between digits
Figure 16.6 Effect of apoptosis during paw development in the mouse 16

17. Genetic Analysis of Early Development: Scientific Inquiry
Edward B. Lewis, discovered the homeotic genes, which control pattern formation in late embryo, larva, and adult stages 17

18. Wild type Mutant Eye Leg Antenna Figure 16.8
Figure 16.8 Abnormal pattern formation in Drosophila
Leg
Antenna 18

19. Cloning Plants and Animals

20. Totipotent cells
Cells that can give rise to all specialized cell types are called totipotent 20

21. Researcher John Gurdon found that when early frog embryo nuclei were transplanted into enucleated egg, most developed into tadpoles
Nuclei from fully differentiated cells, most did not develop

22. Egg with donor nucleus activated to begin development
Figure 16.11
Experiment
Frog embryo
Frog egg cell
Frog tadpole UV
Fully differ-
entiated
(intestinal) cell
Less differ-
entiated cell
Donor
nucleus
trans-
planted
Donor
nucleus
trans-
planted
Enucleated
egg cell
Egg with donor nucleus
activated to begin
development
Results
Figure Inquiry: Can the nucleus from a differentiated animal cell direct development of an organism?
Most develop
into tadpoles.
Most stop developing
before tadpole stage. 22

23. Process worked with mammals
Clones tend to have some faulty genes affecting lifespan

24. Figure 16.13
Figure CC, the first cloned cat (right), and her single parent 24

25. genetically identical to mammary cell donor Results
Figure 16.12
Technique
Mammary
cell donor
Egg cell
donor 1 2
Nucleus
removed
Cultured
mammary
cells
Egg cell
from ovary 3
Cells fused
Cell cycle
arrested,
causing cells to
dedifferentiate
Nucleus from
mammary cell 4
Grown in culture
Early embryo
Figure Research method: reproductive cloning of a mammal by nuclear transplantation 5
Implanted in uterus
of a third sheep
Surrogate
mother 6
Embryonic
development
Lamb (“Dolly”)
genetically identical to
mammary cell donor
Results 25

26. Stem Cells of Animals
Main reason researchers want to clone human embryos is for the production of stem cells
A stem cell - unspecialized cell that can differentiate into specialized cells of one or more types 26

27. Cell division White blood cells
Figure 16.14
Stem cell
Cell
division
Stem cell
and
Precursor cell
Figure How stem cells maintain their own population and generate differentiated cells
Fat cells or
Bone cells or
White
blood cells 27

28. Two types of stem cells:
Embryonic: can differentiate into any type of cells
Adult: not able to differentiate into all cell types

29. Embryonic Stem (ES) cells are pluripotent, capable of differentiating into many cell types
Researchers using retroviruses can reprogram fully differentiated cells to act like ES cells
Cells transformed this way are called iPS, or induced pluripotent stem cells 29

30. Embryonic stem cells Adult stem cells
Figure 16.15
Embryonic
stem cells
Adult
stem cells
Cells that can generate
all embryonic cell types
Cells that generate a limited
number of cell types
Cultured
stem cells
Different
culture
conditions
Figure Working with stem cells
Different
types of
differentiated
cells
Liver cells
Nerve cells
Blood cells 30

31. Concept 16.3: Abnormal regulation of genes that affect the cell cycle can lead to cancer
The gene regulation systems that go wrong during cancer are the same systems involved in embryonic development 31

32. Types of Genes Associated with Cancer
oncogenes - cancer-causing genes
The normal version of these genes, called proto-oncogenes, code for proteins that stimulate normal cell growth and division 32

33. within the gene within a control element
Figure 16.16
Proto-oncogene
Proto-oncogene
Proto-oncogene
Translocation
or transposition:
gene moved to
new locus, under
new controls
Gene amplification:
multiple copies of
the gene
Point mutation:
within
the gene
within a control
element
Oncogene
Oncogene
Oncogene
New
promoter
Figure Genetic changes that can turn proto-oncogenes into oncogenes
Normal growth-
stimulating protein
in excess
Normal growth-
stimulating protein
in excess
Normal growth-
stimulating
protein in
excess
Hyperactive or
degradation-
resistant
protein 33

34. Tumor-suppressor genes encode proteins that help prevent uncontrolled cell growth34

35. Inherited Predisposition and Other Factors Contributing to Cancer
Individuals can inherit oncogenes or mutant alleles of tumor-suppressor genes 35

36. DNA breakage can contribute to cancer, thus the risk of cancer can be lowered by minimizing exposure to agents that damage DNA, such as ultraviolet radiation and chemicals found in cigarette smoke
Also, viruses play a role in about 15% of human cancers by donating an oncogene to a cell, disrupting a tumor-suppressor gene, or converting a proto-oncogene into an oncogene 36