Lecture 10 - Invertebrate models - sea urchin & C. elegans Flashcards
(44 cards)
Why is a sea urchin a good genetic model?
- large number of embryos
- experimental manipulation
Why are genetic models good?
- bred easily in a lab
- genes within the genome can be altered to study their effect on development
What are sea urchins?
echinoderms
What are echinoderms?
deuterostomes
In protostomes, where does the blastopore form from?
the mouth
In deuterostomes, where does the blastopore form from?
the anus
Why are sea urchin’s embryos useful?
transparent embryo, which is large & easily accessible for manipulation
How long does it take for a blastula to develop in a sea urchin?
4 hours after cell division - meaning they have a strict order & orientation
When is the primitive gut formed in a sea urchin?
during gastrulation movements
How does the extensions on the plateaus larva form?
the larva has internal calcareous skeleton that is responsible for the extensions on the plateaus larva
What were the 2 types of development discussed surrounding sea urchins?
mosaic model and regulative development
What is the mosaic model (Weissman)?
the nucleus of the egg contain determinants that specify different fates to different cells by specific segregation to these cells.
What is the regulative development model?
cells are communicating and differences can be generated DE NOVO by cell-to-cell communication
What divisions do sea urchins have in their early stages?
- 2 divisions along the animal-vegetal axis
- 1 perpendicular to these divisions, separating the animal from the vegetal half
In what way are the first 2 cleavages in the development of a sea urchin made?
First 2 cleavages are perpendicular
In what way is the 3rd cleavage cut?
Perpendicular - and separates the 4 animal cells from 4 vegetal cells
Where does gastrulation occur?
at the vegetal pole
How was the sea urchin’s development suggested to be regulative?
if determinants were present, as suggested in the mosaic model, then you wouldn’t get a normal embryo, from a single blastomere
- separated 2 blastomeres at the 2 cell stages
- didn’t get 2 half embryos, but rather got 2 smaller complete embryos
How was the sea urchin development suggested to be mosaic?
- splitting the embryo at the 4 cell stage indicated that development was regulative.
- splitting the 8 cell embryo in a ventral & dorsal half showed that there is at least this axis a degree of mosaicism is present.
- normal embryo not found - instead there was an animalised and vegetalised incomplete larve - meaning there appears to be some form of mosaicism.
- now known that the localised determinists for this are in the cytoplasm rather than the nucleus.
Why do we use genetic model organisms?
by looking at what ‘goes wrong’, you can infer the normal role of that gene on development
What are the ideal characteristics for ease of genetic analysis?
- small organism (because they need to keep large numbers)
- large batches of embryos
- short generation time
- easy to breed
- easy scoring of phenotypes of +/-
- sequenced genome
What are the main anatomical parts of C elegans?
mainly consists of a gut & reproductive organs. Also has muscles that allow it to move & neurons and sensory cells that can convey information to the animal about the environment is navigating
Why are C. elegans good gene model organisms?
- C. elegans develop rapidly
- hatches from egg within 24 hours at normal temperatures
- develops as a hermaphrodite (first male, then female) - use its own sperm to fertilise eggs
- occasionally male only individuals occur - these can mate with females.
- thus prevents continuous inbreeding, which would be detrimental for their fitness
Describe the cleavages of a C. Elegans
1st cell division create: AB & P1 cell
- P1 cell - P2 & EMS
- AB cell - ABa & ABp
ABa (anterior)
ABp (posterior)
