This summary is written in English. It's a summary of the lessons and the prof's website together. The drawings that the prof made on board are also included in the summary.
Chapter 1: Overview of vertebrate development ............................................................................................ 3
The frog development ......................................................................................................................................... 4
Life cycle ......................................................................................................................................................... 4
Egg .................................................................................................................................................................. 4
Cortical rotation.............................................................................................................................................. 4
Cleavage ......................................................................................................................................................... 4
Blastula ........................................................................................................................................................... 5
Mid-blastula transition ................................................................................................................................... 5
Gastrulation .................................................................................................................................................... 6
Neurula ........................................................................................................................................................... 8
Tadpole ........................................................................................................................................................... 9
Hatching.......................................................................................................................................................... 9
The mammalian development .......................................................................................................................... 10
Life cycle ....................................................................................................................................................... 10
Cleavage ....................................................................................................................................................... 10
Compaction .................................................................................................................................................. 10
Blastocyst...................................................................................................................................................... 11
Implantation ................................................................................................................................................. 12
Gastrulation .................................................................................................................................................. 13
Neurulation................................................................................................................................................... 15
Embryo turning ............................................................................................................................................. 15
Lineages and time scale ................................................................................................................................ 15
Chapter 2: Experimental embryology ............................................................................................................ 16
Regulative versus Mosaic development ............................................................................................................ 16
A. Weismann................................................................................................................................................. 16
W. Roux ........................................................................................................................................................ 16
H. Driesch...................................................................................................................................................... 16
S. Horstadius ................................................................................................................................................. 17
H. Spemann .................................................................................................................................................. 18
Cytoplasmic determinants ................................................................................................................................ 18
Blastomere separation ................................................................................................................................. 18
Nieuwkoop’s experiments ............................................................................................................................ 18
Induction ........................................................................................................................................................... 19
The Spemann organizer ................................................................................................................................ 19
Lineage and fate map of the frog gastrula.................................................................................................... 20
The specification map ................................................................................................................................... 21
The organizer in the mouse embryo............................................................................................................. 21
Fate maps of vertebrate embryos ................................................................................................................ 22
Summary of inductive events ....................................................................................................................... 22
Molecular mechanisms ..................................................................................................................................... 23
...................................................................................................................................................................... 23
Beta-catenin and Dishevelled ....................................................................................................................... 23
Mesoderm induction .................................................................................................................................... 25
Gene detection in Spemann’s organizer....................................................................................................... 25
1
, Goosecoid in the frog .................................................................................................................................... 25
Goosecoid in the mouse ............................................................................................................................... 27
Frzb-1 in the frog gastrula ............................................................................................................................ 27
Frzb-1 is a Wnt antagonist ............................................................................................................................ 28
Frzb-1 in the mouse ...................................................................................................................................... 30
Diffusion and the role of antagonists ........................................................................................................... 30
...................................................................................................................................................................... 30
Genes from the Spemann organizer ............................................................................................................. 30
Chapter 3: Organogenesis ............................................................................................................................. 30
Somite patterning and muscle formation ......................................................................................................... 30
Somite formation.......................................................................................................................................... 30
Inductive signals ........................................................................................................................................... 31
Muscle specification ..................................................................................................................................... 32
Axial specification ......................................................................................................................................... 33
Hox complexes, expression and mutants ..................................................................................................... 34
Limb formation.................................................................................................................................................. 35
Limb bud formation ...................................................................................................................................... 35
Limb bud initiation........................................................................................................................................ 35
Limb bud specification .................................................................................................................................. 35
Specification of the Proximo-Distal axis ....................................................................................................... 36
Hox and the identity along the P-D axis........................................................................................................ 37
Specification of the Antero-Posterior axis .................................................................................................... 37
...................................................................................................................................................................... 38
Specification of the Dorso-Ventral axis ........................................................................................................ 38
Apoptosis and digit formation ...................................................................................................................... 38
Chapter 4: Drosophila development ............................................................................................................. 39
Techniques ........................................................................................................................................................ 39
Polytene chromosomes ................................................................................................................................ 39
Enhancer trap ............................................................................................................................................... 39
Development ..................................................................................................................................................... 40
Life cycle ....................................................................................................................................................... 40
Overview of embryonic development .......................................................................................................... 40
Cleavage ....................................................................................................................................................... 41
Mitosis .......................................................................................................................................................... 41
Morphogenesis and Fate map ...................................................................................................................... 41
Gastrulation .................................................................................................................................................. 42
Formation of the adult ................................................................................................................................. 42
Establishment of the body axes ........................................................................................................................ 42
Maternal genes ............................................................................................................................................. 42
Zygotic Dorso-Ventral genes......................................................................................................................... 46
Zygotic Antero-Posterior genes .................................................................................................................... 48
Homeotic genes ............................................................................................................................................ 52
2
,Chapter 1: Overview of vertebrate development
Early development is in 4D (3 spatial + 1 time)
Focus on early stages of development from fertilization to neurula stage
à model organisms:
- amphibians (frogs) have large eggs (easy to manipulate), Xenopus laevis is used bc can
produce eggs in the lab at any time
- Mouse: only mammal that can be studied genetically, mutant, and transgenic animals can be
created, crossed, and analyzed; Is very similar to the human development
- Chick embryo
- Fish will not be discussed
Circle of life: the stages of animal development
Most patterns of embryogenesis are variations of 5 themes:
1) Immediately after fertilization, cleavage occurs. Cleavage is a series of rapid mitotic divisions wherein
the volume of the zygote cytoplasm is divided into numerous smaller cells. These cells are called
blastomeres, and by the end of cleavage, they generally form a sphere known as a blastula.
2) After the rate of mitotic division has slowed down, the blastomeres undergo dramatic movements
wherein they change their positions relative to one another. this series of extensive rearrangements is
called gastrulation, and the embryo is said to be in the gastrula stage. As a result of gastrulation, the
embryo contains three germ layers: the ectoderm, the endoderm, and the mesoderm.
3) Once the three germ layers are established, the cells interact with one another and rearrange
themselves to produce tissues and organs. This process is called organogenesis. Many organs contain
cells from more than one germ layer. Also, during organogenesis, certain cells undergo long migrations
from their place of origin to their final location (such as blood cells, lymph cells, pigment cells and
gametes).
4) In many species, a specialized portion of the cytoplasm gives rise to cells that are the precursors of
the gametes (the sperm and egg). The gametes and their precursors are called germ cells, and they are
set aside for reproductive function. All the other cells of the body are called somatic cells. this separation
of somatic cells and germ cells is often on of the first differentiation to occur during animal development.
The germ cells eventually migrate to the gonads, where they differentiate in gametes.
5) In many species, the organism that hatches from the egg or is born is not sexually mature. Indeed, in
most animals, the young organism is a larva that may look significantly different from the adult. Larvae
often constitute the stage of life that is used for feeding or dispersal.
3
, The frog development
Life cycle
- Xenopus laevis à Order: Anura, Family Pipidae (tongueless frogs)
- South Africa
- 7,5 - 14 cm, males smaller
- Entirely aquatic (easy for lab) and carnivorous
- Females can be induced to lay eggs by injection of hCG
(human Chorionic Gonadotropine)
- Originally used as fertility test: inject urine from woman (zie
⬆)
- Egg can be fertilised in vitro using minced testis
- Must kill the male frog and use the
spermatozoïden, lay on the eggs and these will be
fertilized
- Embryos can be manipulated
- Speed of development depends on the temperature
Figure 1: Life cycle
Egg
-Diameter ≈ 1 mm à human is 10 times less
- Dark pigmented hemisphere (Animal pole), and pale one
(vegetal pole)
à oocyte is radially symmetrical around its Animal-
Vegetal axis
- Yolk platelets (providing ‘food’) are heavy and mostly in
vegetal pole
- Due to gravity: animal pole always on top and vegetal pole
on bottom
- The middle white dotted part is the pronucleus: the future
half of the nucleus of the zygote Figure 2: Egg
Cortical rotation
- Sperm entry point: top left à ALWAYS!
- Upon fertilization —> membrane will change to prohibit further
sperm penetration
- Less than 30 min after, the cortex will rotate relatively to
the bulk of the cytoplasm and yolk
= Cortical rotation
à 30° rotation towards the sperm entry point
- Cytoskeleton = responsible
- Visible change bc animal hemisphere is pigmented
Figure 3: Cortical rotation
(linked to cortex)
- Opposite side to entry point = devoid of pigment
- Critical for original asymmetry of embryo
- Generally, point of sperm entry is on ventral side of embryo and opposite to it, the dorsal side
will form (gastrulation will start here)
Cleavage
- 1st cleavage: vertically
- Passing through animal and vegetal pole
- Generally, also pass by the point of sperm entry
- Cleavage furrow starts @ animal pole àslowly down
4
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