Lecture 2 - Animal Devlopment Flashcards
Morphogenesis
Occurs via changes in cell position, shape, survival, and form of organs
- rearrangement of cells or sheets
Fertilization
Haploid gametes join to form a diploid zygote
Model Organisms
Easy to study but broadly representative
- Development al genes and mechanisms are similar across animal species
-Studying development in model organisms provides knowledge about development in general
Gametes in sea urchins
Sperm and egg are the haploid gametes
-Egg cytoplasm contains many proteins and mRNA involved in early development
Fertilization in sea urchins - step 1
Sperm contact with the jelly coat triggers the acrosomal reactions
- This is what allows the sperm to reach the egg - the kind of softening of the egg
Differential Gene Expression
Foundation of diverse cell types and behaviors through development
Fertilization in sea urchins - step 2
Surface proteins on acrosomal process bind to receptors on egg cell membrane
Fertilization in sea urchins - step 3
Plasma membrane fuse, triggering fast block to polyspermy
- polyspermy - the oocyte is penetrated by more than one sperm
-fast block is a reversal of polarization to repel the other sperm
Fertilization in sea urchins - step 4
The sperm nucleus enters and the cortical reaction causes a slow block to polyspermy
-Perivitelline space occurs - a physical separation from the outside and inside of the egg, this is the slow block
Fertilization in sea urchins - step 5
Fusion of sperm and egg nuclei form the diploid nucleus of the zygote - there is a small clear envelope around the zygote called the fertilization envelope
Cleavage
-the process by which the zygote becomes multicellular
-Rapid cell division with little growth of individual cells
(G1 and G2 phases
skipped)
-results in blastomeres
Blastomeres
smaller cells resulting from cleavage
What does cleavage result in?
-Cells getting smaller and smaller with each round of division
- No growth of cells between divisions
In frogs
Zygote becomes a blastula
Blastula
A hollow ball of cells with a fluid-filled cavity called the blastocoel
-There is an animal pole and a vegetal pole
- where sperm hits the egg becomes the animal pole (smaller cells, less ‘yolky’)
Differential gene expression
- cells express different genes depending on their location and the stage of development
- expressing different genes leads to the production of different proteins (this, in turn, determines the structure and behaviors of the cell at any given time)
Cytoplasmic determinants
A signal given within the cell determines how the gene is expressed
-molecules within the cytoplasm regulate gene expression
- can be differently distributed to daughter cells resulting in differences in gene expression
Inductive signals
A signal from outside of the cell determines how the gene is expressed
-The signal molecules that a cell is exposed to depends on its location within the embryo, and the stage of development
Embryotic stages - Cleavage
converts the unicellular zygote into a multicellular embryo
Embryotic stages - Blastula
a hollow ball of cells
Embryotic stages - Gastrulation
where the three germ layers are formed
Gastrulation
Stages when the three germ layers are established and the basic body plan is set up
-Results in a three-layered gastrula
Organogenesis
formation of the organs
neurlation
formation of the nervous system
- is an example of organogenesis
Three layers of gastrula
ectoderm, mesoderm, endoderm
Frog gastrulation - step 1
Cells in the vegetal hemisphere push inwards
Frog gastrulation - step 2
outer cells (future endoderm and mesoderm) roll inwards
Frog gastrulation - step 3
Blastocoel collapses and a new cavity - archenteron is formed
Frog gastrulation - step 4
Cells at the animal pole (future ectoderm) spread over the outer surface
Convergent extension
example of cells changing their position
- produces a longer, narrower structure
- an example of morphogenesis
ectoderm
will form the skin, nervous system, and sense organs
mesoderm
will form the skeleton, muscles, and hearts
endoderm
Will form the digestive system and respiratory tube
Formation of the neural tube - step 1
Ectodermal cells change shape during neural tube formation
Programed cell death
-Changes the shape of the embryo
