Chapter 1- “The anatomical tradition”
• ______________- progressive change in
multicellular organisms
• ___________- study of animal development
• _________________ = development +
embryology
Big questions
•
•
•
•
What dictates _________________?
How can cells form ordered ___________?
How are _________ cells set apart?
How do cells know when to stop
_____________?
• How do cells know where to ___________?
Historical setting
Pre-1800s - Two theories
1. ___________ theory– All organs prefigured,
but very small
– Backed by science,
religion, philosophy
2. ______________
– All organs made de
novo (from scratch)
•Early 1800s- staining techniques/microscopy
disprove preformation theory•The birth of “_______________”
•Late 1800s- _______ (instead of goo) theory
recognized
Fate mapping- the mapping of
cell lineage
Strange terminology
• _____________- Organisms with three
primary germ layers
• _______________- lack a true mesoderm
• Hydra, jellyfish, sponges
• ________________- Cells receiving cues
from other cells
Four Principles“Von Baer’s laws”
1. ___________features appear prior to ______________ ones
– All vertebrates have gill arches, notochords, primitive kidneys
2. Less general characters are developed from _______ general (i.e.
specialized from non-specialized)
– Scales vs. feathers
– Legs vs. wings
– Nails vs. claws
3. An embryo does not pass through the ___________________ of
other, lower creatures
4. Thus, the early embryo of a higher animal in never like a lower
animal, but only like it’s ___________________.
– Humans never look like ____________
Fate mapping
Major layers1. _____________•
•
•
Outer embryo layer
Skin
Nerves
2. ______________•
•
•
Inner embryo layer
Digestive tract
Respiratory system
3. _____________•
•
•
•
•
•
•
•
Middle layer
Blood
Heart
Kidney
Gonads
Bones
Connective tissue
Muscle
“Homologous” vs “Analogous”
Human arm
• “________________”Similarity arising from a
common ancestral
structure
– e.g. bird wing and
human arm
• “_______________”Similar function, but not
common ancestor
– e.g. bird wing and
insect wing
Seal limb
Bird wing
Bat wing
Teratology
• Environmental agents causing disruption of
development -called “________________”
• Example- __________________ (1961)
Chapter 2- Life cycles
• All animals follow similar life cycle
– __________________- mixing of genetic
material between sperm and egg
– ___________________- events between
fertilization and hatching (or birth)
General Animal Development
2. _________________-
1. __________- One cell is
subdivided into many cells to form a
blastula
Extensive cell rearrangement to
form endo-, ecto- and meso-derm
4. _________________- produce
3. ____________________- Cells
germ cells (sperm/egg) Note: Somatic
cells denote all non-germ cells
rearranged to produce organs and tissue
The Frog Life cycle
Animal pole
100’s of fertilized eggs
Unfertilized egg
(Stained)
Vegetal pole
Single egg,
early blastula
Note: Cells get smaller, but
egg ___________ remains the
same!
The Frog Life cycle- gastrulation through neurula
1. _______________________________ forms at “belly”
2. Dorsal blastopore lip becomes
the ____________ (a circle)
3. Ectoderm cells encase
4. Mesoderm cells migrate inside
along blastopore edges
5. Neural folds and groove appear
Fig. 2.3
The Frog Life cycle- metamorphosis
A unicellular protist
The “goo” theory can work!
Species 1
A single cell
3 cm long!
Nucleus
(in Rhizoid)
Species 2
What happens if we
swap nuclei??
Sexual reproduction
Sex and reproduction are two distinct processes
•Sex- mixing of genetic material from two individuals
•Reproduction- creation of new individuals
•Bacteria, amoeba- Reproduction without sex
•_________________- Sex without reproduction
Swap “micronuclei”
then separate
•________________- Sex with reproduction
Chlamydomonas
(A eukaryote)
“Plus”
“Minus”
Asexual
reproduction
Sexual
reproduction
Chromosome
mixing
“Plus”
“Minus”
Fig. 2.8
Unicellular eukaryotes have basic developmental
processes observed in higher organisms
•Mitosis and meiosis is accomplished
•Sexual reproduction
•Chromosomal structure is stable and similar
But, multicellular organisms are a whole new ball game
These require cell-cell communication and distinct cell functions
“_________________________________”
Example –
Volvox
Example –
Volvox
Principle 1 :
One cell ______________ into 4-64 cells
Single cell
Chlamydomonas
Gonium
Panadorina
2000 cells
Somatic cells
(appear as dots)
Germ cells
Eudorina
Pleodorina
Volvox
Fig. 2.11
Principle 2 :
___________________ of cell typessomatic vs reproductive
Multicellular aggregation to from a slug- Dictystelium
Principle 3 : _______ cells instructed to perform specific functions
Travel to new food source
A _______ is
formed
(2-4 mm )
Fig 2.17
>10,000 cell
_____________
This cycle
requires adhesion,
_____________
and
______________.
Differentiate into
_______ and spore
case
Stalk dies, spores released
Individual cells Start here
General Animal Development (From chapter 2)
1. ________- One cell is subdivided
into many cells to form a blastula
2. __________- Extensive
cell rearrangement to form endo-,
ecto- and meso-derm
4. _______________- produce germ 3. _____________- Cells rearranged
cells (sperm/egg) Note: Somatic cells
denote all non-germ cells
to produce organs and tissue
Chapter 3- Experimental Embryology
• Three major approaches
1. External forces - ____________________
2. Internal forces- ____________________
3. Organ development (Morphogenesis)
1. External forces
Fig. 3.1
a. Sex determination
•Boellia- depends on where larva lands
•Alligator egg temperature - <30C = _________ development
b. Embryo ______________
•Butterflies- colors depend in season
•Frogs and UV light
Summer
Spring
Chapter 3- Experimental Embryology
2. Internal forces
A few definitions
____________________- development of specialized cell types
____________________- developmental fate is restricted
Two stages1. ___________________- capable of becoming specific
cell types, but decision is reversible
2. __________________- non-reversible cell fate decision
a. __________________specification- blastomere cell fate is determined
at blastula stage (e.g. isolated blastomere will become same type if
removed from blastula)
Most ________________ do this
Chapter 3- Experimental Embryology
2. Internal forces (continued)
b. ______________ specification- cell fate is determined on where a cell
finds itself (e.g. isolated blastomere will become what surrounding cells dictate)
Transplant cells
All ___________ do this
Normal
development
c. Note- insects display
__________ Specificationcell fate is determined in
egg cytoplasm
Cell fate dictated
by location
Removed cells
are compensated
Fig. 3.11
Chapter 3- Experimental Embryology
2. Internal forces (continued)
More definitions__________- soluble molecule that instructs cells to differentiate
Concentration ___________- A morphogen at different concentrations
depending on location of cell
Example of concentration gradient- the flatworm (Hydra)
It grows back!
The French
flag analogy
to understand
gradients
2. Internal forces (continued)
A lot makes blue
French Flag
Analogy
A modest amount makes white
A little makes red
Transplanted tissue retain
it’s _____________, but
differentiates
according to
new _______________
Fig. 3.19
2. Internal forces (continued)
An example of a concentration gradient- Activin levels dictate
cell fate in Xenopus
Activin
levels
Fig. 3.20
2. Internal forces (continued)
A _________________ field- a group of cells whose
position and fate are specified with respect to the
same set of boundaries.
•The general fate of a cell group (e.g. tissue) is determined,
but individual cells within that tissue can respond to
new positional cues
Example- a “_______ field”
-Transplantation of cells specified for limb development results
in limb formation in new place
Tree frog
-But nearby cells will form a limb
Salamander
If remove limb
bud, surrounding
cells will form
the limb
Fig. 3.22
Nematode infection disrupts
normal limb field
3. Morphogensis
Morphogenesis is the bigger question of how cells within a
given organ are in a precise place and have a precise function.
1. How are _________formed from populations of cells?
2. How are __________ constructed from tissues?
3. How do organs form in particular ____________, and
how do migrating cells reach their destinations?
4. How do organs and their cells grow, and how is growth
____________________ throughout development?
5. How do organs achieve ____________? Compare leg and
finger cross-sections- the same yet different.
3. Morphogensis (continued)
Observations- Mix cells from different cell types in a culture
dish, they migrate to pre-instructed location.
Mesoderm
+ epidermis
Mesoderm
Mesoderm + endoderm
+ endoderm +epidermis
How do the cells
“know” where to go?
One modelThe ____________ model
Malcolm Steinberg 1964
3. Morphogensis (continued)
Surface
tension
The _____________ model
20.1
Cells interact so as to form an
aggregate with the smallest
_________________free energy
12.6
In other words, those
with stronger _________
properties move to the
_________ of a cell mass
Adhesion is dictated by
1. Number of cell adhesion molecules
2. Type of cell adhesion molecules
8.5
4.6
1.6
Fig. 3.30
3. Morphogensis (continued)
_____________ – Calcium-dependent adhesion proteins
- a major class of proteins that mediate cell adhesion
•Establish intercellular connections
•Required for _____________ segregation
•Required for organization of animal formation
Cadherin
Cadherins bind to
__________in cells, which
bind to actin cytoskeleton
Catenins
Fig. 3.31
3. Morphogensis (continued)
Cadherin types
___-cadherin- in all mammalian embryos, then restricted
in epithial tissues of embryos and adults
___-cadherin- primarily in placenta
___-cadherin- in mesoderm and developing central nervous system
____-cadherin-required for blastomere adhesion
Cadherins are responsible
for cell sorting
Cells with different
cadherin _____sort
Cells with different
___________ sort
Fig. 3.31