L10 Invertebrate models: Sea Urchin and C. Elegans Flashcards
Why are sea urchins taken for invertebrate models?
- Sea urchin: large number of embryos, experimental manipulation
- Genetic Models, here breeding is easily done in a lab.
- Genes within the genome can be altered to study their effect on development.
What does Echinoderms mean?
The name “echinoderm” comes from Greek words meaning “spiny skin.”
What does Deuterostomes mean?
The word “deuterostome” comes from Greek, meaning “second mouth
In deuterostomes, the anus develops first, and later, a separate, second opening forms, and this becomes the mouth
Can all Sea urchins be deuterostomes?
All seas urchins are Echinoderms.
Echinoderms are Deuterostomes so yes
What is a protosome?
A protostome is an animal in which, during embryonic development, the first opening (the blastopore) becomes the mouth
How long does it take a plateaus to form from a blastula?
13 days
What happens to the fertilised egg minutes after fertilisation?
The fertilized eggs cleave and form a 2 cell stage in 120 minutes, in the next 120 minutes a 64 cell blastula is formed.
What happens to the fertilised egg hours after fertilisation?
The 64 cell blastula undergoes gastrulation forming a gastrula.
What happens days after the egg is fertilised?
In 5 days the last gastrula undergoes hatching forming a pluteus larva wich is then metamorphised forming the adults in 50 days.
What is the mosaic development/model?
Weissman put forward the Mosaic model
-a variant of this is where cytoplasmic determinant control cell fate
What is the regulative development model?
The regulative development model highlights the remarkable ability of some embryos to adjust and compensate for perturbations during early development, ensuring the formation of a complete organism.
What two types of development did sea urchins experiments contribute to?
Mosaic or regulative development
What is the animal and vegetal pole?
The animal and vegetal poles represent regions of the egg with distinct compositions and developmental fates. They are fundamental to the organization and development of the embryo, particularly in organisms with yolky eggs.
Explain how sea urchins’s eggs develop
Sea urchins have a stereotypic set of early divisions…all embryos undergo cell division in exactly the same way
2 divisions at right angles along the Animal-Vegetal axis
1 perpendicular to these divisions, separating the animal from the vegetal half
How was it discovered that sea urchin development can be regulative?
Hans Driesch showed in a classic experiment that in the sea urchin development can be regulative. Because when he separated the two blastomeres at the 2 cell stage he did not get 2 half embyos, rather he got two smaller but complete embyos. this showed it is regulative development.
What is a gene?
Genes are present on the DNA in a chromosome in the nucleus.
When they are active they are transcribed into mRNA by a RNA polymerase, the mRNA is exported to the cytoplasm.
The RNA is translated by the ribosomes into a protein …this is what usually executes the biological functions of the gene.
What is a wild type gene and a mutant gene?
The wild type gene represents the standard version, while the mutant gene represents a variant that has arisen due to changes in the DNA sequence.
What are the ideal characteristics for genetic analysis? (6)
- Small organism
- Large batches of embryo
- Short generation time
- Easy to breed
- Easy scoring of phemotypes
- Sequenced genome
How fast does the C elegans develop and hatch from the egg?
They develop rapidly and hatch from the egg within 24 hours at normal temperature.
What does hermaphrodite mean?
The term “hermaphrodite” refers to an organism that has both male and female reproductive organs.
In stereotypical cleavage pattern, at which cleavage does the pattern become asymmetric?
The first cleavage is asymmetric.
What are the roles of Par 3 and Par 2 genes?
In C. elegans embryonic development, the Par (Partitioning defective) proteins, including Par-3 and Par-2, play crucial roles in establishing and maintaining cell polarity and asymmetric cell division during the early stages of embryogenesis.
If the lineage is invariant, is the cell fate determined then?
The cell fate is NOT absolutely determined
How does apoptosis ensure proper development? (3)
Apoptosis is essential in:
* Formation of reproductive organs Male/Female
* Skin between digits
* Immune system maturation
How is apoptosis essential for homeostasis?
Mitosis/Apoptosis to maintain constant number of cells
Removal of damaged cells (DNA damage, Viral infections)
What can improper regulation of apoptosis lead to?
Autoimmune disease
Cancer
What is the role of RNA interference (RNAi)?
A powerful mechanism to control gene activity:
Double stranded RNA triggers a biochemical process that degrades identical mRNAs, thus it blocks gene activity after transcription has happened.
Again this pathway was to a large degree worked out in C elegans
Discovered while studying muscle development in C. Elegans
How many cells is c elegans made up of and how many are precisely programmed for apoptosis?
C Elegans is made of 1090 cells but precisely 131 cells are programmed to die: Apoptosis
How does RNA interference work (RNAi)?
Double stranded RNA triggers a biochemical process that degrades identical mRNAs, thus it blocks gene activity after transcription has happened
