L2 - Germ Cells Flashcards
What is seen during development in terms of potency and specialisation
See a gradual restriction in potency of multipotent cells to specialised comitted cell fates
Cells initially are
Totipotent
Define pluripotent
Able to form all of the tissues of the body except the placenta `
Describe what happens in the first 3 weeks post fertilisation
Body axes are gradually established
What type of cells are set aside for the next generation
Gonadal germ cells
In many animals there is an early division between __________ and ________ cells
Somatic and germ
What is interesting RE somatic cells in plants
Are able to form new organims
Where are the primordial germ cells determined
In a specific location on the edge or outside of the developing embryo
PGCS
Primordial germ cells
Where do PGCs migrate to
What do they become here
Migrate to the gonad
Become the progenitor population for eggs and sperm
What do you need (2) for the determination of the germ cells
Totipotent (plastic) cells
Cell which is capable of underogoing meiosis
Describe how the nematode worm gave us conceptual understanding about the formation of germ cells
Nematode worm has a specfic no cells (lineage can be traced)
Early assymetric divsions leads to the formation of the P lineage
This cell makes its way to the posterior of the cell
Describe how asymmetric cell division takes place
Coupling the polarisation of the cytoplasmic determinants to the oriented plane of cell division
What does the P cells act as
Pre germ cell
Throughout asymm divisions what to the P cells inherit
Describe their composition
P-granules
Mix of protein and RNAs
Describe how the P-granuel work
Binds to the DNA of the P cell and block alsmost all transcription and differentiation
Block translation in the cytoplasm
Promote stem cell fate and stimulate meiosis
Describe what is seen when Nem worm P cells are stained for transcriptional
There is no transcriptional act
Similar P-cell exist in vertebrates
Where are they found
Always at the posterior
Germ line established which shows:
Little transcription and translation –> no differentiation
Able to undergo meiosis
What mechanisms are involved in the shutting down of PGCs
Epigenetic silencing
Histone modifications (methylation and deacetylation) DNA methylation
PGCS arised from __________________
Extra-embryonic mesodendodermal cells
Where do PGCS stay during axes formation
What is the reaosning behind this
Beyond the posterior part of the embryo
Protected form signals which are specifying the body axes
Why are PGCs pluripotent
Because genes that code for differentiation factors are repressed transcriptionally and translationally
When to PGCs migrate
Once rapid differentiation of embryogenesis begins to decrease
Describe the migration of the germ cells
Passively ride the endoderm - attaches to endoderm to migrate through the midgut then attaches to the mesoderm
Where is the final destination of the PGCs
Gonadal niche
In the ovaries cells attach to the
Stromal caps
In the testes the cells attache to
Hub cells
Describe the migration of the PGCs in chick/mouse/human
Migrate throguh the posterior (hindgut) along a fibronectin rich trail
Then leave the gut to move more laterally to the genital ridges
What is the function of the gonadal niche
Provision of a specialist microenvironment which protects the PGCS in their pluripotent state
Descrive the travelling stem cell niche idea
Support cells travel with PGCs secreting SCF to maintain the undiffernetiated cell type
What is SCF
Stem cell factor
What is the affect of a mutation which means SCF is unable to be produced
Stem cells are no longer protected and would differnetiate
What is the affect of a mutation which means that the chemoattractant is no longer produced
Would get stuck in the gut and would fail to make it to the niche
Describe how PGCS can lead to formation of teratomas
Failure to migrate to the protective niche would lead to the formation of teratomas
What structure do cells at the periphery of the mammalian blastocyst form and from what fate is this
Cells on the outer periphery of a human/mammal embryo assume a different fate; the trophectoderm that forms the placenta
What is the name given to the cells that occupy the inside of the trophoblast
Inner cell mass
What is the significance of the cells inside the trophoblast not occupying the full space
The cells of the inner cell mass cluster at one side, the cells closest to the trophectoderm will give rise to the epiblast whereas the cells furthest from the trophectoderm will give rise to the hypoblast
From which region of the human embryo are human ES cells found
Inner cell mass
Define a stem cell
A cell capable of endless self-renewal and can give rise to a daughter that can give rise to several lineages
How is a progenitor cell different to a stem cell
A progenitor cell is only capable of limited self-renewal as well as limited differentiation propensities
What are the names given to the stem cells found in the mature tissues
Adult stem cells or tissue specific stem cells
As development proceeds, most somatic cells become differentiated and not mitotic, T or F
T
Describe the potency of adult stem cells
Multipotent or pluripotent
What is meant by cellular homeostasis
Cellular homeostasis is the constant or periodic generation of new cells to replace old, damaged, and dying cells, or the addition of new cells as needed.
Give an example of where cellular homeostasis changes during life
Pregnant females produce more red blood cells. RBCs are made continuously through life from haematopoietic stem cells in the bone marrow. Haematopoietic stem cells respond to increased levels of oestrogen found in pregnant females, to become hyper-activated and make many more daughter cells
Adult regeneration/repair that occurs routinely in these tissues occurs via a very different mechanism to how they were first generated in the embryo, T or F
F - adult tissue regeneration/repair mirrors the way the cells form in the embryo
What is meant by the niche in which tissue specific stem cells reside
complex microenvironments around the stem cells, made up of many cells, that interact with the environment and the stem cell to decide whether to activate it
Haematopoietic stem cells give rise to all the blood cell types, what two classes of blood cells are these
Myeloid cells – monocytes, macrophages, neutrophils, basophils, eosinophils and erythrocytes as well as megakaryocytes/platelets and dendritic cells. Lymphoid cells – T, B and NK Cells
Other than in the bone marrow, where else are HSCs found
Umbilical cord and placental tissue
Stem cells respond to physiological signals, T or F
T
What can the factors released by the adjacent cells of the HSC niche act to achieve
Regulate stem cell activity and the decision as to whether to remain quiescent, or become active. They can also trigger division to give another HSC or a daughter that will differentiate
In which three regions are neural stem cells found
Subventricular zone lining the lateral ventricles, the subgranular zone and in the hypothalamus lining the 3rd ventricle
What is the other name of neural stem cells
Neural precursor cells
