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Animal Developmental Biology - Lecture notes - Lecture 1
Animal Developmental Biology
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Animal Developmental Biology Lecture 1 1. Fertilization Zygote (single cell) Animal Development Adult
2. Model systems (easy to study, yet representative of animal development more generally)
a. The frog
b. The fish
c. The chick
d. The mouse
e. The worm
f. The fly
• Conjoint twins
• Distinct from the shoulders up
• Died 8 months old
• Only adults in America joined at the head, 42 years old
• Pennsylvania
• Share bone, tissue and blood lines, joined at corner of left eye
• Share brain tissue, but have individual identities
• Siamese twins
• Comes from two siam twins that had joined livers
• Proclaimed their oneness
• Seen as having political or religious significance
• Signify political union…
• Conjoined twins as a natural phenomenon
• The heart apex is pointing down to the right
• Spleen is on the right
• Stomach is on the right
• All of ours are on the left
• Cytosinversis (left to right reversal of the internal organs; rare but in conjoined twins)
• Seen in Rita and Christina
• 13 days after conception, embryo begins to organise itself (gastrulation)
• Gives the embryo its geometry
• Remove the membrane surrounding the egg, to it upside down, and excise the tissue, then graft into
another embryo on the other side
• Would the transplanted cells behave differently from the hosts?
• Almost all of the embryos died
• Transplanted cells organised the host cells into an extra, but conjoined creature
• Individual cells don’t govern their own fates
• Organiser limited the potential of cells around it, was the origin of order
• Organiser = clump of cells
• Amsterdam = museum with collection of mutants
• Terrontolity? – study of monsters
• Most of the specimens in the museum are mutants,
• Mermaid syndrome
• Legs are fused together, feet protrude like flippers
• Usually fatal because it affects many organs, like the heart
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• Midline disorder, lower half of body collapses in on itself
• Operations took plastic surgery to a new level, lower half of body had to be completely rebuilt
• Tiffany, only person in the world to survive with it to the age of 16
• Causes of it have been obscure, but knew it was the organiser
• Needed to find the substance secreted by cells in the organiser
• Discovery was called Corden – it was a signalling molecule Retinoic acid
• If you cut the tale off a tadpole it regenerates, but if you put it in retinoic acid you get a tangle of legs
• Last body part to form – Face
• Pig that has 2 faces, 2 snouts, 4 nostrils, 3 eyes (Called Ditto)
• Had an optic nerve that connected to the third eye, but unsure if he could see through it
• Chicken with 2 upper beaks
• Sonic gene – place a soaked bead in a different area in the embryo, but still in the face region

Lecture 2 • Xenopus
o Page 43 in Gilbert
o Red part is the Deuterostomes which include the vertebrates
• Deuterostomes

• Page 27
• Fertilization (0h. 1 cell) Cleavage (rapid cell divison = 6h. 10,000 cells) Gastrulation (re-arrangement
of cells from interior to exterior, generates 3 germ layers; 10h. 30,000 cells)
Organogenesis/Neurulation (generates the organs, infold of cells from the dorsal surface to give rise to
the CNS; 19h. 80,000 cells) Larval stages (110h. 1,000,000 cells) Maturity …
• Cell division occurs precisely from the animal pole at the top, bottom is the vegetal pole?
o Can be seen clearly as its pigmented o Higher concentration of yolk at vegetal pole o Yolk
inhibits cytokinesis (division of the cell)
• Cleavage furrow moves down through the embryo to reach the vegetal pole
• Second cell division starts to take place, when first division is still incomplete
• Third cell division starts before second has finished, at right angles to first 2 divisions; embryo now
divided up into 8 cells o 4 at the animal pole, 4 at the vegetal pole o Smaller cells at the animal pole and
larger cells at the vegetal pole
• Blastula is the final stage o 10s of thousands of cells, with fluid filled cavity (blastocoel) towards animal
pole
• Individual cells referred to through these stages are blastomeres
• Cells of the animal pole will give rise to the ectoderm, cells around vegetal pole gives rise to endoderm,
and cells around equatorial region give rise to the mesoderm
• Cell division occur every 30 mins, very rapid
• Single cell zygote is over 1mm across, 1000 larger then a bacteria
• Genomes that need to be duplicated are so much larger than in the bacteria
• The embryo never grows in diameter, it just undergoes organisation Each cell generated all has its
own copy of the genes
• Blastula then undergoes gastrulation
• Mid-blastular transition – when cell division stops and cells start to re-arrange = gastrulation
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• The cells start to fold into the interior from the dorsal surface (back of the animal) o Cells left on outside
are the dorsal-blastopore lip?
• Ectoderm gives rise to the outside surface, endoderm will line the inside/gut of the animal, mesoderm
fills the middle
• Archenteron = fluid filled cavity Gives rise to the lumen of the gut
• As it folds in, the mesoderm forms between the 2
• Ectoderm cells move around the outside at the endoderm folds in
• Few endoderm cells still left on the outside, which is the yolk plug o ….
• As the endoderm folds in, it reaches the other side of the embryo, and where it comes into contact with
the ectoderm with no mesoderm = where the mouth forms (secondarily)
• Anus forms at the connection between the archenteron and …
• Deuterostome comes from
o Means mouth forming secondarily
• Neurulation o To generate the CNS
• Small circle is the notochord, mesodermal tissue, runs from head to tail just below the surface o Send
signals to overlying ectoderm that they’re going to give rise to the
CNS
o That region of the ectoderm are going to fold into the interior, which generates a neural
groove as the cells fold up and close over
o To pinch off the neural tube running all the way down the back
• Neuropore closure failure
o The ends cant be sealed up o Not only in the frog, but in us as wel o The ends are referred to
as Neuropores
o Has serious consequences (exposes brain the outside service so it degenerates =
anencephaly; if tail end fails to close = spina bifila)
• Vertebrate cloning was achieved a long time ago
• King, 1952 o Blastula stage nuclei in Rana pipiens
o Transferred those to anucelated zygotes (nucleus removed) o Embryo would develop fine
through to adult stage
• Gurdon, 1962
o Differentiated tadpole intestinal nuclei in Xenopus laevis
o Low success of the experiment o But could be increased by …
o Shows a fully differentiated cell could be used to create a new individual, and could generate
all the different cell types the animal needed The information was still retained even after it
was fully differentiated
• Fate Maps
o A map of the fates of the cells that are present in the embryo at a particular time
o Glastular stage (label cells on outside using a dye, follow through the development, and can
see what cells are derived from the previously labelled cells)
• Highly regulative development
• If placed on the ventral side (belly rather than back), then the planted cell gives off signals telling the
embryo…
• …
• Second embryo that formed is largely composed of cells from the host…
• 1-cell stage
o up to 80 mins
• 2-cell, 4-cell, 8-cell stages o up to 25 mins