L2 - Gastrulation and Stem Cell Niche Flashcards
What sort of potency does a zygote have?
Totipotent
Where does differentiation take place in the embryo?
Differentiation takes place in all 3 germ layers from early stages of embryogenesis
All have different derivatives
Totipotent –> pluripotent –> multipotent
Do cells stay as multipotent cells?
The vast majority of cells don’t stay as multipotent cells – they differentiate
When does embryonic organogenesis occur?
2 months post fertilisation
How are adult stem cells formed?
Some cells set aside, undifferentiated, to contribute to individual over its lifetime
How are gonadal germ cells formed?
Some cells set aside, undifferentiated, for the next generation
Specialised totipotent cells
This helps maintain the species
Where do gametes arise and migrate to?
Arise from primordial germ cells
Migrate into the gonads
In which plants and animals can somatic cells readily form new organisms?
Cnidarians, flatworms, tunicates
In which animals is there an early division between somatic and germ cells?
Insects, vertebrates
Where do primordial germ cells arise and migrate to?
- Primordial germ cells are determined in a specific location on the edge or outside of the developing embryo
- They migrate to the gonad and become the progenitor population for eggs and sperm
What do you need for germ cell differentiation?
A totipotent cell type
A cell capable of undergoing meiosis
Where do P cells come from?
C.elegans
How are P cells formed?
In early cleavage and gastrulation, asymmetrical divisions produce a specialised cell - P-lineage cell
P cells produced is smaller and inherits different cytoplasmic determinants
- At posterior end
How is the P cell made different from other cells?
Cell division plane is a crucial determining factor in the fate of 2 daughter cells
In a mother cells with cytoplasmic determinant that is asymmetrically localised division along meridian creates?
Maintains two daughter cells, both identical to mother
Two self-renewing stem cells
In a mother cells with cytoplasmic determinant that is asymmetrically localised division along equator creates?
Progenitor and a cell with different determinants
Can now differentiate
Why are some determinants in the cytoplasm polarised?
They are found at one end of the cell
Through asymmetric division P-cells inherit?
Specialised P-granules
Found in the cytoplasm but can get into the nucleus
Mix of proteins and RNA
What is the role of P granules?
Bind to DNA of P cell and block almost all transcription
- Thus block all differentiation
In cytoplasm block translation
Some gene transcription upregulated to promote stem cell fate and cause cells to undergo meiosis
What is the version of P cells in vertebrates?
Germ cells
What is the role of germ cells in vertebrates?
Germ cells in all species express the translational blocker, Nanos This shows - Little transcription or translation - Thus no differentiation - Thus a pluripotent identity - Also they can undergo meiosis
How are PGCs controlled?
PGCs are shut down transcriptionally and translationally
How are PGCs shut down?
Epigenetic Silencing mechanisms include
- DNA methylation - represses gene activity
- Histone modification - histone proteins govern accessibility of gene promoters
Where do PGCs arise from?
Arise from extra-embryonic mesodendodermal cells just beyond posterior part of the embryo
As the body axes form, PGCs stay in this position
- Future posterior part of hind gut
What are the characteristics of mammalian primordial germ cells?
Arise from extra-embryonic mesodendodermal cells just beyond posterior part of the embryo
As the body axes form, PGCs stay in this position
- Future posterior part of hind gut
How do germ cells migrate in the Drosophila?
Germ cells passively ride endoderm – up through the duct
Chemoattractive and repulsive cues drive PGCs and gonad precursor cells together and to the gonad
PGCs divide through the larval stage and differentiate at metamorphosis
Where do PGCs attach to in the ovaries?
Stromal cap
Where do PGCs attach to in the testes?
Hub cells
How do germ cells migrate in the chick, mouse and human?
- PGCs stay out of the embryo while the major inductive events occur
o Body axes formation and early organogenesis - PGCs migrate though the hind gut along a fibronectin trail
- Move laterally to the genital ridges which produce a chemoattractant
- Ultimately found in the gonads which provide a specialised microenvironment that
o Protects the PGCs in their pluripotent state
o Supports their meiotic divisions and formation of eggs or sperm cells
How are migrating germ cells protected from differentiating?
The travelling stem cell niche idea
- Support cells travel with PGCs to maintain the undifferentiated stem cell phenotype
- They secrete stem cell factor (SCF)
What causes the formation of a teratoma?
Failure to migrate to protective niche/failure to make SCF causes germ cells to differentiate
