Lecture 2 - Vertebrates from egg to embryo Flashcards
What makes an animal a vertebrate?
has a head, dorsal nerve chord & notochord
notochord = precursor to modern day vertebrate
Describe the similarity/differences in early embryonic development in vertebrates
SIMILARITIES
- once a level of polarity
DIFFERENCES
- oocytes if different sizes
- formation of an embryo is very different
What stage of embryonic development is consistent between vertebrates?
phargyngula stage
What highly repeated structures were observed by Haeckel?
- vertebrates tend to have 5-9 pharyngeal pouches
- somites are also repeated
- meta metric structures - repeated modules - SEGREGATIO
What is likely to have caused the similarities in development in vertebrates?
a ‘bottle-neck’ during developmemnt that are evolutionarily conserved
What occurs after the sperm meets the egg?
cleavage (division) occurs synchronously
What is the name given to cells when dividing?
blastomeres
What occurs during the blastula stage?
- cells are on the outside of the inside cavity
What is the name given to cells on the exterior during the blastula?
blastoderm
What is the name given to cells in the cavity during the blastula stage?
blastocoel
How often do cells in the embryo tend to divide?
Every 30 minutes
What is the equation to work out the number of cells in early cell proliferation?
N(start) x 2^(txf) = N finish
N = number of cells
t = time
f = frequency
What occurs directly after sperm entry?
a wave of free Ca2+ (calcium) ion travel across the egg.
What is the purpose of the wave of calcium after sperm entry?
- allows development to proceed, as calcium acts on proteins that controls the cell cycle to initiate cleavage (cell division)
What occurs to ensure that cell division is synchronised?
- oscillations in Ca2+ levels during early development.
- small release of calcium before divisions where cleavage is occurring
What stages are there in the cell cycle in the early embryo?
“rapid synchronous cleavage”
- S&M phase only, no G phase
What process is suppressed in the cell cycle in the early embryo?
transcription
What provides the building blocks for DNA synthesis & growth?
maternal store (RNA & protein)
What occurs in the S stage?
synthesis - DNA replication
What occurs in the M stage?
mitosis - nuclear division
cytokinesis - cytoplasmic division
Describe what happens to the maternal RNA & zygotic RNA levels after zygotic genome activation
after zygotic genome activation, maternal RNA falls, with zygotic RNAs rising
What are the characteristics of zygotic genome activation?
- cell cycle slows
- cell cycle becomes asynchronous
- cell movement begins
When does zygotic genome activation occur in a mouse?
2-cell stage
When does zygotic genome activation occur in a frog?
5,000-cell stage
What occurs during gastrulation?
formation of the 3 germ layers:
- ectoderm (outside)
- mesoderm
- endoderm
(involves the complex rearrangement of tissues)
How do the endoderm & mesoderm form?
movement of cells to the inside of the embryo
How does the ectoderm form?
the cells that remain on the surface of the embryo form the ectoderm
What axis are established as a result of gastrulation?
establishment of true dorsal/ventral axes
What are the derivatives of the ectoderm?
- neurones
- glia
- epidermis
- pigment cells
What are the derivatives of the mesoderm?
- muscle
- cartilage, bone
- dermis
- kidney
- heart
- blood
What are the derivatives of the endoderm?
- gut
- lungs
- associated organs
What are the epithelial cells like in the first tissue?
structured & tend to be cuboidal. They can migrate but usually come together as a sheet or cluster
What are mesenchymal cells like in the first tissue?
move easily and are amorphous (no defined shape)
What can be said about mesenchymal cells that are held tight together?
they have undergone condensation
What can epithelial cells turn into?
mesenchymal cells (and visa versa)
What are the forces that drive cell & tissue rearrangements?
cytoskeletal rearrangement occurs as a result of a change in the expression of cell surface proteins (cell adhesion molecules)
What are the different types of cytoskeletal rearrangements that can occurs as a result of a change in the expression of cell surface proteins?
- migration
- localised cell proliferation
- cell death
What is morphogenesis?
The creation of shape
What are the stages of embryonic development in a zebrafish?
early cleavage –> cleavage –> somitogenesis
What do somites form in zebrafish?
- anterior to posterior
- form on either side of the neural tube
What is underneath the neural tube?
notochord (precursor of vertebrate)
Where & when do somites form?
form following gastrulation in the mesoderm
Where do mesenchymal cells gather towards the end of gastrulation?
dorsally
What leads to the segmentation of different structures in the adult?
is the result of segmentation during somitogenesis
What are the 2 mesodermal progenitors in the somite?
Dermomyotome - dermis & skeletal muscles
Sclerotome - vertebrae & ribs
How many vertebrae does one somite give rise to?
2 halves of a vertebrae
How is it that trunk muscles are also segmented?
this occurs as we maintain muscle segmentation in an adult
What is the neural tube composed of?
brain & spinal cord
Where does the neural tube arise from?
ectoderm
What is the name given to the process by which the neural tube is formed?
neurulation
