Germ layer and gastrualation Flashcards
From the zygote, what two types of tissue are going to form?
Embryonic and Placental
What are the three germ layers and examples of what they give rise to?
Ectoderm- epiderimis, nevous system
Mesoderm- notochord, kidneys, blood, bone, muscles
Endoderm- lining of GI tract and respiratory system, liver, pancreas
What does multipotent mean?
Has the ability to differentiate into a set number of cell types- cannot go back in the differentiation program.
What are adult stem cells?
Cells that are set aside during embryogenesis which will contribute to the organism over time
What are gonadal germ cells?
Specialised cell set aside in an undifferentiated state for the next generation. - they maintain the species
What are primordial germ cells?
Give rise to gametes. They arise outside of the gonads and migrate into them. They are specified through a combination of autonomous and non autonomous signals and they reside in the gonadal stem cell niche
What do you need for germ cell determination?
The cell must be totipotent (it is going to be part of the zygote which is, by definition totipotent.
The cell must be capable of undergoing meiosis
What is invariant lineage?
E.g. C.elegans- all cells in every organism are specified and patterned in exactly the same way- this made them very useful for fate mapping experiments
What are P-lineage cells?
A cell type in C.elegans which arises early on through an asymmetrical division to produce a specialised cell- they are always maintained in the most posterior aspect and they eventually give rise to germ cells
How does the P cell arise?
Planes of division separating cytoplasmic determinants. They inherit P granules that are in the cytoplasm and can enter the nucleus.
What is the purpose of the P granules?
Bind DNA of P cell- prevents nearly all transcription and thus differentiation.
Block translation in cytoplasm (just in case)
Promote stem cell fate- cause cells to undergo meiosis
What are the properties of the mammalian P cell equivalent?
Always lies in the posterior aspect of the developing embryo- not actually in the embryo, but slightly outside
Do germ cells differentiate?
No, they have a specific set of specialised proteins which prevent the transcription and translation of genes which means there is no differentiation. They therefore have a plastic/pluripotrent identity
How do you control widespread transcriptional decisions?
Because P cells shut down all transcription, this has lead to a lot of work to look at the mechanisms of genome wide shut down.
Epigenetic silencing mechanisms include DNA methylation
Which germ layer do primordial germ cells arise from?
Extra-embryonic mesoendodermal cells, just beyond the posterior part of the embryo. They remain outside as body axis development occurs. They sit in their silenced state behind what will be the anus.
Why are the germ cells on the outside of the embryo?
They are away from/protected from the signals which are causing organogenesis
When do the PGCs enter the body?
After rapid differentiation of the body begins to decrease approx. 8 weeks PF.
What is the process of migration of the PGCs in Drosophila?
- Specified in posterior extraembryonic tissue
- Migrate in through the gut
- When they reach the mid-gut, they move out into the gonadal niche
What determines sperm or egg?
The niche- in Drosophila the female niche is called the stromal cap cells and in males it is the hub
What is the process of PGC migration in humans/mice/chicks?
PGC stay outside to avoid differentiation signals.
Migrate through the gut along a fibronectin trail
Leave the gut and move laterally into
the genital ridges
Here they find their niches
What is the genital ridge?
Found either side of the gut and arise from intermediate mesoderm. They secrete a chemical which serves as a chemoattractant which guides PGCs into the gonads from the gut
How are the PGCs protected from differentiation as the migrate?
They have cells called support cells which travel with them to maintain the undifferentiated phenotype by secreting a stem cell factor
What is the impact of a failure of PGCs to migrate into the protective niche
Germ cell differentiation- teratoma
What is a teratoma?
Enormous growths of lots of different types of tissues- the stem cells essentially differentiate into a vast array of different tissues
