Download Cell signaling • Fertilization (3 ligand-receptor pairs

Review from last
lecture
•  Cell signaling
•  Fertilization (3 ligand-receptor pairs)
– Resact/receptor
– Jelly coat factor/receptor
– Bindin/fertilizin
•  The acrosome reaction
•  Preventing polyspermy
Outline Questions
Understanding Cell Proliferation and Cleavage
•  How is cell proliferation used in the growth of developing tissues?
•  What are the post-fertilization stages of development?
–  How many cells do they have?
•  What is cleavage?
–  What are the different forms of cleavage found in different animals?
•  What are maternal determinants
–  How do they direct early development?
–  How can this help to define body axes?
•  How do cells move?
–  What structures are created or destroyed to give directional movement?
Bio200
Proliferation and Cleavage
Cell proliferation
•  If cells are signaled correctly, they will begin
proliferating
–  Controlled but rapid mitosis
–  Good for building or restoring structures
–  Cells sometimes made in large amounts, and then
differently regulated to several cell fates
Cell proliferation
•  If cells are signaled correctly, they will begin
proliferating
–  Controlled but rapid mitosis
–  Good for building or restoring structures
–  Cells sometimes made in large amounts, and then
differently regulated to several cell fates
•  The initial proliferation from zygote to embryo is
called cleavage
–  This refers to the cleavage furrow, which is the
earliest readily-recognizeable feature of cell
division
–  Often driven by packaged material in the oocyte
–  Maximizes speed of growth, as the cell does not
have to wait for massive transcription and
translation
Cell division
http://www.youtube.com/watch?v=28GTvrNvRRE
These were taken at the same magnification.
What can you tell about cell size?
Cleavage Patterns: Examples
Fertilized egg
Radial cleavage:
Spiral cleavage:
Discoidal cleavage:
Blastula
Example: Many deuterostomes
Example: Snail
Example: Birds
Yolk
Superficial cleavage:
Example: Fruit Fly
Cells
Yolk
Cleavage Patterns: Examples
Fertilized egg
Radial cleavage:
Spiral cleavage:
Discoidal cleavage:
Blastula
Example: Many deuterostome
Example: Snail
Example: Birds
Yolk
Superficial cleavage:
Example: Fruit Fly
Cells
Yolk
Cleavage Patterns: Examples
Fertilized egg
Radial cleavage:
Spiral cleavage:
Discoidal cleavage:
Blastula
Example: Many deuterostome
Example: Snail
Example: Birds
Yolk
Superficial cleavage:
Example: Fruit Fly
Cells
Yolk
Cleavage Patterns: Examples
Fertilized egg
Radial cleavage:
Spiral cleavage:
Discoidal cleavage:
Blastula
Example: Many deuterostome
Example: Snail
Example: Birds
Yolk
Superficial cleavage:
Example: Fruit Fly
Cells
Yolk
Rapid progression from one cell to many
http://www.youtube.com/watch?v=XSKh-GLQn4E
Early stages of development:
Common terminology
•  Zygote
–  2N fertilized post-oocyte cell
•  Morula
–  A small ball of cells resulting from early
proliferation
•  Blastula
–  Hollow ball of cells, where regulation has
started cell movements
Early stages of development:
Common terminology
•  Zygote
–  2N fertilized post-oocyte cell
•  Morula
–  A small ball of cells resulting from early
proliferation
•  Blastula
–  Hollow ball of cells, where regulation has
started cell movements
•  Early Gastrula
–  Larger embryo, either having or starting to
have formed cell layers
•  Late Gastrula
–  Significantly developed early embryo,
with cell layers formed
Maternal determinants:
Pre-loaded developmental material
•  Follicle cells allow the mother
to load materials into the egg
–  Nutrients
–  Directions!
•  Information-containing molecules
that help the young egg develop
•  Could be proteins, RNAs, etc
•  Spatial localization is crucial
What are cytoplasmic determinants, and how
do they affect the consequences of cleavage?
•  Stylea partita has
~transparent embryos so
you can follow fate of cells,
based on pigmented areas
in egg.
•  Observation 1: From “fate
mapping”
•  What can you conclude from
this observation?
Transcription in early embryos
Experiments with α‐amanitin
(Amanita = “death cap” and
“destroying Angel” mushrooms):
inhibits RNA polymerase.
In frogs: cleavage occurs normally if
embryos are treated with α‐
amanitin.
What can you conclude from this
observation?
Preferential polymerization:
Directional and signaled crawling
nucleus
Preferential polymerization:
Directional and signaled crawling
nucleus
Cell Movement Video
http://www.youtube.com/watch?v=sHFN48il9YY
Cell actions in development
Key Concepts
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Cell proliferation is the use of repeated rounds of mitosis to build tissues by increasing the
number of cells.
Most zygotes undergo cleavage and then go through the following early-development stages:
morula, blastula, gastrula
Different species use different cleavage geometry and patterning. Within a species, all cleavage
patterns will proceed from one cell to many organized cells.
Specific RNAs and proteins deposited in the oocyte by the mother help to jump-start
development.
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Cells can move:
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Using the polymerization and depolymerization of filaments
In response to signals
Directionally, by preferentialy locating polymerization enzyme in the cell
The five basic processes by which cells help to create a developing organism are:
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These maternal determinants may help define early developmental decisions.
Maternal genotype may determine some of the embryos phenotypic characteristics.
Apoptosis
Differentiation
Signaling
Proliferation
Movement
Organisms use these basic processes in rigorously controlled combinations to ensure
development of new, complicated, consistent structures.