Ontwikkelingsbiologie Dier & Plant
College “Principles of Animal Development”
Concepts of animal development.
• Cleavage
→ the series of cell divisions by which a single fertilized egg cell is transformed into a multicellular
body, the blastula.
Blastocoel = cavity inside the blastula.
In humans: 7 days for the blastocyst to
implant in the endometrium.
Blastocyst & Blastula = same thing.
Morula “moerbei” stage = when the blastula
has around 16 cells, it will look like a morula.
This is applicable to both the human and the
echinoderm blastula.
• Determinate and Indeterminate growth
Determinate growth Indeterminate (continuous) growth
Mammals: body growth stops at sexual Mammals: only hair & nails grow continuously
maturity. through life.
E.g. snakes grow in size even after sexual maturity. They shed their skin (ecdysis) to make room.
Development stops at sexual maturity. Development = from zygote to sexual maturity. After this:
senescence = ageing.
• Epigenesis vs. Preformation
Preformation theory = organisms are already fully-formed in miniature in the gonads and develop
simply by enlarging. → bullshit
Epigenesis = organismal complexity appears de novo during development.
e.g. limbs: start as a bud and slowly develop into a limb with fully grown skeleton and surrounding
flesh.
, • Gastrulation
After cleavage → gastrulation.
Gastrulation involves:
- The formation of 3 germ layers → ectoderm, mesoderm, endoderm.
- The development of the notochord.
- The appearance of the head-tail axis (primary axis).
Frog:
Chick:
Homologous process in both species.
Think of chick as smushed down frog. When cells from the germ layers move in to form the primitive
streak, this is where the notochord will form.
Ectoderm: makes the whole nervous system and the epidermis (skin).
Mesoderm: makes notochord, skeletal system, excretory system and muscular system.
Endoderm: makes
the lining of the
gut, the
respiratory
system (lungs)
and the urethra,
urinary bladder
and reproductive
system. Mostly
organs.
, • Induction
➔ The stimulation of one embryonic region by another, by means of a signal, causing it to
develop or differentiate in a certain way.
Nobel prize winning experiment:
Spemann-Mangold organizer graft.
Transplant of dorsal lip of blastopore
(Spemann organizer) to a new place
→ induces second body axis.
• Morphogenesis
➔ “A change of shape”.
Classic example is neurulation: you
start of with a neural plate and then it
rolls op into a tube, the neural tube.
• Neurulation:
After gastrulation → neurulation.
• Pattern formation
➔ “The spatial organization of cell differentiation”.
How do cells know where to differentiate in the right way? → Organizer (signalling) regions that
secrete signalling molecules.
E.g. wing of chick embryo only has digits 2, 3 and 4. How do
each of these digits know which one they are? → signalling
region called the zone of polarising activity (ZPA). In this
zone a bunch of cells secrete the ‘sonic-hedgehog’
recombinant protein which forms a gradient. The cells read
of their position from this gradient. If they get a strong blast
of sonic they make digit 4, a little weaker they make digit 3,
and a weak signal makes digit 2.
Experiment: implanting a bead filled with sonic on the
other side of the limb bud confuses the cells and results in a
mirror image duplication of the digits.
• Regulation
➔ “The process whereby an embryo adapts its structure in order to compensate for
disturbances or damage, so that it develops as a complete whole.”
e.g. if a blastula is split early enough, it will develop into 2 whole organisms.
, • Segmentation
➔ “The development of repeating structures”.
e.g. somites (vertebrae develop from somites which are formed by the mesoderm during
segmentation), rhombomeres (segments in hind brain), body segments in insects.
• Stem cells
Stem cells show asymmetric cell division.
This means stem cells do not only
differentiate, they can also replace
themselves. This is the case in asymmetric cell
division.
Stem cells can be found in the bone marrow,
inside bones, the epidermis of the skin and
the lining of the gut. This is why cancers often
occur in these regions.
Potency in stem cells:
- Totipotent: can generate all the cells in the body. E.g. a fertilized egg is totipotent.
- Pluripotent: can generate many different lineages but not the whole embryo. E.g. skeletal
muscle and nerve and blood cells.
- Multipotent: can generate a restricted lineage. E.g. many different types of blood cells.
College “Birth Defects”
Congenital malformation = where embryonic development (morphogenesis/pattern formation) has
gone wrong.
Congenital → present at birth. The anatomy of the baby is changed. 3-5% of pregnancies have a risk
of malformation.
Causes of birth defects:
- Inherited = genetic e.g. mutation in Pax6 => aniridia
- Environmental = teratogens e.g. softenon/thalidomide => phocomelia
➔ Or both ! e.g. cleft lip
Teratogens cause malformations, such as:
- Toxicants e.g. ethanol
- Viruses e.g. rode hond
- Drugs e.g. softenon
- Radiation
College “Principles of Animal Development”
Concepts of animal development.
• Cleavage
→ the series of cell divisions by which a single fertilized egg cell is transformed into a multicellular
body, the blastula.
Blastocoel = cavity inside the blastula.
In humans: 7 days for the blastocyst to
implant in the endometrium.
Blastocyst & Blastula = same thing.
Morula “moerbei” stage = when the blastula
has around 16 cells, it will look like a morula.
This is applicable to both the human and the
echinoderm blastula.
• Determinate and Indeterminate growth
Determinate growth Indeterminate (continuous) growth
Mammals: body growth stops at sexual Mammals: only hair & nails grow continuously
maturity. through life.
E.g. snakes grow in size even after sexual maturity. They shed their skin (ecdysis) to make room.
Development stops at sexual maturity. Development = from zygote to sexual maturity. After this:
senescence = ageing.
• Epigenesis vs. Preformation
Preformation theory = organisms are already fully-formed in miniature in the gonads and develop
simply by enlarging. → bullshit
Epigenesis = organismal complexity appears de novo during development.
e.g. limbs: start as a bud and slowly develop into a limb with fully grown skeleton and surrounding
flesh.
, • Gastrulation
After cleavage → gastrulation.
Gastrulation involves:
- The formation of 3 germ layers → ectoderm, mesoderm, endoderm.
- The development of the notochord.
- The appearance of the head-tail axis (primary axis).
Frog:
Chick:
Homologous process in both species.
Think of chick as smushed down frog. When cells from the germ layers move in to form the primitive
streak, this is where the notochord will form.
Ectoderm: makes the whole nervous system and the epidermis (skin).
Mesoderm: makes notochord, skeletal system, excretory system and muscular system.
Endoderm: makes
the lining of the
gut, the
respiratory
system (lungs)
and the urethra,
urinary bladder
and reproductive
system. Mostly
organs.
, • Induction
➔ The stimulation of one embryonic region by another, by means of a signal, causing it to
develop or differentiate in a certain way.
Nobel prize winning experiment:
Spemann-Mangold organizer graft.
Transplant of dorsal lip of blastopore
(Spemann organizer) to a new place
→ induces second body axis.
• Morphogenesis
➔ “A change of shape”.
Classic example is neurulation: you
start of with a neural plate and then it
rolls op into a tube, the neural tube.
• Neurulation:
After gastrulation → neurulation.
• Pattern formation
➔ “The spatial organization of cell differentiation”.
How do cells know where to differentiate in the right way? → Organizer (signalling) regions that
secrete signalling molecules.
E.g. wing of chick embryo only has digits 2, 3 and 4. How do
each of these digits know which one they are? → signalling
region called the zone of polarising activity (ZPA). In this
zone a bunch of cells secrete the ‘sonic-hedgehog’
recombinant protein which forms a gradient. The cells read
of their position from this gradient. If they get a strong blast
of sonic they make digit 4, a little weaker they make digit 3,
and a weak signal makes digit 2.
Experiment: implanting a bead filled with sonic on the
other side of the limb bud confuses the cells and results in a
mirror image duplication of the digits.
• Regulation
➔ “The process whereby an embryo adapts its structure in order to compensate for
disturbances or damage, so that it develops as a complete whole.”
e.g. if a blastula is split early enough, it will develop into 2 whole organisms.
, • Segmentation
➔ “The development of repeating structures”.
e.g. somites (vertebrae develop from somites which are formed by the mesoderm during
segmentation), rhombomeres (segments in hind brain), body segments in insects.
• Stem cells
Stem cells show asymmetric cell division.
This means stem cells do not only
differentiate, they can also replace
themselves. This is the case in asymmetric cell
division.
Stem cells can be found in the bone marrow,
inside bones, the epidermis of the skin and
the lining of the gut. This is why cancers often
occur in these regions.
Potency in stem cells:
- Totipotent: can generate all the cells in the body. E.g. a fertilized egg is totipotent.
- Pluripotent: can generate many different lineages but not the whole embryo. E.g. skeletal
muscle and nerve and blood cells.
- Multipotent: can generate a restricted lineage. E.g. many different types of blood cells.
College “Birth Defects”
Congenital malformation = where embryonic development (morphogenesis/pattern formation) has
gone wrong.
Congenital → present at birth. The anatomy of the baby is changed. 3-5% of pregnancies have a risk
of malformation.
Causes of birth defects:
- Inherited = genetic e.g. mutation in Pax6 => aniridia
- Environmental = teratogens e.g. softenon/thalidomide => phocomelia
➔ Or both ! e.g. cleft lip
Teratogens cause malformations, such as:
- Toxicants e.g. ethanol
- Viruses e.g. rode hond
- Drugs e.g. softenon
- Radiation
