L2 Vertebrates from egg to embryo Flashcards
What are vertebrates?
Vertebrates are all organisms that have a backbone or a vertebral column
What are chordates?
Chordates are a phylum of animals that share several key features
What are the key features of a chordate?
-Head (with a brain)
-Dorsal nerve cord - runs along their back (dorsal side) and is hollow
-Notochord - flexible rod that provides skeletal support
Do vertebrates all develop the same way?
No they develop in different ways. However during the pharyngeal stage, they look similar
Can you give me examples of vertebrates? (10)
Hagfish
Lampreys
Chondrichtyes. (Sharks)
Ray-fined fish
Lung-fish
Amphibians
Snakes, lizards, birds
Mammals
What is the Pharyngula stage?
This stage is a critical period in the embryonic development of vertebrates. It’s a stage of remarkable similarity across different vertebrate species
What are somites?
Somites are transient (lasts a short time) but vital structures in vertebrate embryos.
Somites form in a repeating pattenr along the body axis, giving rise to the segmented appearance of the vertebrate body plan
What is segmentation?
Dividing metameric structures into repeated units/segments
Explain the early stages of development.
- Sperm and oocyte combine (Fertilisation) to for a zygote.
- Zyogote undergoes cell divisions called cleavage
- The new divided cells form a hollow ball called blastomeres.
- As cleavage continues, blastomeres eventally form a solid ball of cell called a morula
- Morula rearrange themselves to form a hollow sphere called a blastula
What is blastula composed of?
Blastoderm on the outside
Blastocoel on the inside
How would you calculate the exponential growth of cells?
N (start) X 2^(tXf) = N (finish)
N = number of cells
t = time
f = frequency of division
For example at 2 hours after fertilisation:
1 X 2^(2X2) = 16 cells
What happens after fertilisation: egg activation?
After sperm entry a wave of free Ca2+ ions travels across the egg
How does calcium promote cell division?
- Calcium acts on proteins that control the cell cycle to initiate cleavage (cell division)
- Oscillations in Ca2+ levels during early development synchronise cell division. Cell divisions are very rapid.
What happens after every round of division in context to calcium composition?
After each round of division, there is a release of calcium from intracellular stores, such as the endoplasmic reticulum. This calcium release is thought to be important for resetting calcium levels and preparing the cell for the next round of division
What are the differences between the cell cycles of early embryo and regular? (4)
- Rapid, synchronous divisions - cleavage
- S (DNA replication) and M (mitosis) phases only; no G phases
- G1 transcription is suppressed.
- Maternal stores (RNA and protein) provide building blocks for DNA synthesis and growth
Maternal stores - Components from the female oocyte.
How is RNA handled at the earlier stages of development?
Maternal RNAs decrease over time in which leads to the activation of zygotic genome activation.
What are the characteristics of the cell after zygotic genome activation?
Characteristics:
* Cell cycle slows
* Cell cycle becomes asynchronous
* Cell movement begins
What does gastrulation mean?
Formation of the three germ layers
What are the 3 layers of germ ?
Endoderm - inside
Mesoderm
Ectoderm - surface
What are the derivatives of Ectoderm? (4)
Developop = derivatives
Neurons, glia, epidermis and pigment cells.
What are the derivatives of endoderm? (3)
Lungs, gut and associated organs.
What are the derivatives of the mesoderm? (6)
Muscle
Cartilage, bone
Dermis
Kidney
Heart
Blood
How does gastrulation work?
Gastrulation involves complex rearrangement of tissues.
What are the cells gastrulation gives rise to?
Epithelial cells and mesenchymal cells.
What does amorphous mean?
No defined shape
What are the first tissues?
Epithelium and mesenchyme
Describe 2 features of mesenchymal cells
Mesenchymal cells move easily and are amorphous ( no defined shape)
Describe 2 features of epithelial cells
They tend to be more structured and tend to be cuboidal
What are the forces that drive cell and tissue rearrangements?
- Cell shape changes.
- Changes in expression of cell surface proteins.
- Migration
- Localised cell proliferation - limbs
- Cell death
What is morphogenesis?
The creation of shape
What is somitogenesis?
It’s the process by which somites form
When does sometogenesis occur?
After gastrulation
Explain the process of sometogenesis
- At the end of gastrulation mesenchymal cells gather dorsally
- Cells on the outside edge of the somite epithelialize to make it distinct from neighbouring tissue.
- The somites then disassemble and revert to mesenchymal cells.
How do somites form?
Somites form from anterior and posterior
Are somites temporary structures?
Yes
What do Sclerotome form?
Vertebrate and ribs
What do Dermomyotome form?
Dermis and skeletal muscles
Where does the neural tube arise from?
From the ectoderm.
Does somite give rise to one vertebrate ?
One somite does not give rise to one vertebrae. It gives rise to two halves of a vertebrae
Are trunk muscles segmented?
Yes
What is neurulation?
Neurulation is the process by which the neural tube forms in vertebrate embryos.
The neural tube will eventually develop into the brain and spinal cord
