Developmental biology
Lesson 1 How is it possible that a complete organism is generated from a single cell?
Preformism
With the spreading of the Preformism theory, sperm cells were seen as cells that could carry
the preformed offspring.
Epigenesis
❖ Epigenesis: embryo develops progressively from an undifferentiated egg cell.
❖ William Harvey (1578-1657, UK)
❖ One of his life’s major works, published in 1651 “On Animal Generation”
❖ He was the first to show that life came from eggs (i.e., embryos from yolk → epi)
Theory of Recapitulation
❖ Development of the embryo goes through stages that represent evolution of
ancestors
❖ Johann Friedrich Meckel (1790s, Germany)
❖ Etienne Serres (1824, France)
❖ Also known as “Embryological parallelism”
Theory of recapitulation by Ernst Haeckel:
“Ontogeny recapitulates Phylogeny”
❖ Ontogeny (embryonic development) represents
phylogeny (history of evolution)
❖ Earliest stages support his claim that they
correspond to a common, ancestral form
❖ Each species seems to recapitulate ancestral
morphologies during its own development
❖ Can be this considered true?
Developmental biology
❖ Organisms arise by a relatively slow process of progressive change = development
❖ Development begins with a single cell—the fertilized egg, or zygote (fully
undifferentiated cell), which divides mitotically to produce all the cells of the body
(fully differentiated cells)
❖ Development does not stop at birth, or even at adulthood.
o Every day we replace >1 gram of skin cells
o Bone marrow generates millions of new red blood cells every minute.
o Regeneration of severed parts (starfish)
o Metamorphosis (frogs, butterflies)
❖ Developmental biology is the discipline that studies embryonic development and
other processes related to organisms’ development.
1
,How is cell polarization (1 side of the cell is different than the other) established and
regulated?
❖ Extrinsic regulation → signal from outside
o Cell is in close contact with an external niche.
o Only one daughter cell can maintain contact with the niche.
❖ Intrinsic regulation → trigger from something present in the cell
o Regulators of self-renewal within the cell are localized asymmetrically.
o They are inherited by only one of the two daughter cells.
Intrinsic regulation
Symmetry breaking in the early C. elegans embryo
❖ When the sperm enters the cell, the symmetry is broken.
❖ The 4 steps are crucial for 2 daughter cells that are different from each other.
2
, PAR Proteins: An internal cellular signal for polarization
❖ Par proteins = Partitioning defective genes
o If you take out a Par protein of the genome (mutation), you will see a
difference in division
❖ Homologs throughout the animal kingdom
❖ Organizing cell asymmetry, co-ordinating polarisation of cytoskeleton
Key features of PAR polarity factors
❖ PAR polarity is well conserved in different cell types of many organisms
❖ They create protein domains which have distinct compositions for different functions
Symmetry breaking in the early C. elegans embryo
❖ On the left side, we will look at C. elegans picture
o Always the anterior side
❖ On the right side
o Always the posterior side
PAR proteins localize in a mutually exclusive manner
❖ Anterior PAR are required to prevent posterior PAR proteins from localising at the
anterior and vice versa
❖ If PAR-2 is mutated, you won’t see a lot in the staining. Depending on what the
interaction is between other proteins and PAR-2, they will show/not show either
❖ Posterior PARs (PAR-2) are required to prevent anterior PAR proteins (PAR-3-PAR-6)
from localizing at the posterior
3
Lesson 1 How is it possible that a complete organism is generated from a single cell?
Preformism
With the spreading of the Preformism theory, sperm cells were seen as cells that could carry
the preformed offspring.
Epigenesis
❖ Epigenesis: embryo develops progressively from an undifferentiated egg cell.
❖ William Harvey (1578-1657, UK)
❖ One of his life’s major works, published in 1651 “On Animal Generation”
❖ He was the first to show that life came from eggs (i.e., embryos from yolk → epi)
Theory of Recapitulation
❖ Development of the embryo goes through stages that represent evolution of
ancestors
❖ Johann Friedrich Meckel (1790s, Germany)
❖ Etienne Serres (1824, France)
❖ Also known as “Embryological parallelism”
Theory of recapitulation by Ernst Haeckel:
“Ontogeny recapitulates Phylogeny”
❖ Ontogeny (embryonic development) represents
phylogeny (history of evolution)
❖ Earliest stages support his claim that they
correspond to a common, ancestral form
❖ Each species seems to recapitulate ancestral
morphologies during its own development
❖ Can be this considered true?
Developmental biology
❖ Organisms arise by a relatively slow process of progressive change = development
❖ Development begins with a single cell—the fertilized egg, or zygote (fully
undifferentiated cell), which divides mitotically to produce all the cells of the body
(fully differentiated cells)
❖ Development does not stop at birth, or even at adulthood.
o Every day we replace >1 gram of skin cells
o Bone marrow generates millions of new red blood cells every minute.
o Regeneration of severed parts (starfish)
o Metamorphosis (frogs, butterflies)
❖ Developmental biology is the discipline that studies embryonic development and
other processes related to organisms’ development.
1
,How is cell polarization (1 side of the cell is different than the other) established and
regulated?
❖ Extrinsic regulation → signal from outside
o Cell is in close contact with an external niche.
o Only one daughter cell can maintain contact with the niche.
❖ Intrinsic regulation → trigger from something present in the cell
o Regulators of self-renewal within the cell are localized asymmetrically.
o They are inherited by only one of the two daughter cells.
Intrinsic regulation
Symmetry breaking in the early C. elegans embryo
❖ When the sperm enters the cell, the symmetry is broken.
❖ The 4 steps are crucial for 2 daughter cells that are different from each other.
2
, PAR Proteins: An internal cellular signal for polarization
❖ Par proteins = Partitioning defective genes
o If you take out a Par protein of the genome (mutation), you will see a
difference in division
❖ Homologs throughout the animal kingdom
❖ Organizing cell asymmetry, co-ordinating polarisation of cytoskeleton
Key features of PAR polarity factors
❖ PAR polarity is well conserved in different cell types of many organisms
❖ They create protein domains which have distinct compositions for different functions
Symmetry breaking in the early C. elegans embryo
❖ On the left side, we will look at C. elegans picture
o Always the anterior side
❖ On the right side
o Always the posterior side
PAR proteins localize in a mutually exclusive manner
❖ Anterior PAR are required to prevent posterior PAR proteins from localising at the
anterior and vice versa
❖ If PAR-2 is mutated, you won’t see a lot in the staining. Depending on what the
interaction is between other proteins and PAR-2, they will show/not show either
❖ Posterior PARs (PAR-2) are required to prevent anterior PAR proteins (PAR-3-PAR-6)
from localizing at the posterior
3
