Lecture 26 Flashcards
What is meant when we refer to early cells of the embryo as totipotent
They can give rise to any of the germ layers and subsequently any cell of the body
Most of the early derivatives of the totipotent cells will remain as adult or tissue specific stem cells, T or F
F – most will differentiate to form the somatic cells of the body
What is the name given to the set of cells set aside in an undifferentiated state that contribute to an individual during its lifetime
Tissue specific or adult stem cells
Tissue specific stem cells are maintained throughout life due to their ability to self-renew, T or F
F – they are gradually depleted over time
What are gonadal stem cells
Another type of specialised cells distinct from tissue specific stem cells that are set aside in an undifferentiated state for the next generation
In some animals as well as all plants, somatic cells can readily form new organisms, T or F
T – whereas in many animals there is an early division between somatic and germ cells
Generation of the germ cells is said to be a two-step process, what are the main stages in this process
The primordial germ cells (PGCs) are determined in a specific location just on the edge or outside of the developing embryo. Then PGCs migrate to the gonad and become the progenitor populations for eggs and sperm
A germ cell is a plastic/totipotent cell type capable of undergoing mitosis, T or F
F – they are capable of undergoing meiosis
C. elegans has given us a conceptual understanding of germ cell determination. What process of early cell division accounts for the differences in germ and somatic cells and is a process used to produce different daughters
Asymmetric cell division
What cell lineage in C. elegans is responsible for giving rise to the germ cells, discuss this lineage
The P-cell lineage in C.elegans gives rise to the germ line. The fertilisied egg goes onto to divide to give the AB cells and the P1 cell. The P1 cell then divides to give an EMS cell and the P2 cell. P2 divides asymmetrically to give the P3 and C cell fates
What causes the process used to create 2 different daughter cells during cell division
Asymmetric cell division is caused by the asymmetric localisation of cytoplasmic determinants within a cell
Describe how localisation of cytoplasmic determinants can both subsequently lead to both symmetrical and asymmetrical cell divisions
Once cytoplasmic determinants are localised within the mother cell, division along a meridian that intersects this localisation would result in the production of two identical daughters after division. However, cell division along the equator adjacent to the determinant localisation would generate two different daughter cells
What are the two daughters produced by asymmetric division in the formation of the germ line
One daughter cell will be maintained as a stem cell while the other will differentiation
Give an example of P-granule determinant that becomes localised during the generation of the P-cell lineage during C.elegans development
PIE1 – a transcription blocker that also subsequently prevents differentiation
Other than blocking transcription, what can other cytoplasmic determinants mediate in the P-cells
Translation blockers, promoters of stem fates, cause cells to undergo meiosis
P-granules become restricted to one cell, this cells will be the germ cell, T or F
T
What is the name of the region in the Drosophila embryo that is responsible for mediating germ line development
Germ plasm
Germ line determination occurs during what process in the Drosophila embryo
Cellularisation
Give an example of a specific gene product localised posteriorly in the Drosophila embryo
Germ cell-less
What is the result of loss of function mutations in some of the gene products involved in determining the germ line in Drosophila and the vertebrate homologues
Sterility
What transcriptional blocker homologue of gcl is found in Xenopus laevis and is expressed at the most vegetal pole of the bottom hemisphere of the frog embryo
Nanos
The frog cells that inherit the gcl homologue will become the primordial germ cells, T or F
T
What is different about the location where the PGCs are determined in mammalian embryos
In mammals, the primordial germ cells are determined outside of the main developing body axes at the junction of the epiblast/hypoblast
What sort of signals must the PCGs in mammalian embryos be prevented from receiving in order to maintain their stem capability
Signals that govern formation of the body axes such as wnts, FGFs, BMPs, Hedgehog and RA
In mammals, differentiation of PGCs is repressed by repressing gene expression until the rapid differentiation of the early embryo begins to decrease. What happens at this stage
The PCGs go inside the embryo and enter the hindgut at the posterior region. The germ cells then migrate to the specialised protective niche of the gonads.
What is meant when referring to the gonads as a protective niche
The gonad regions are a specialised protective microenvironment that prevent the PGCs from differentiating
Describe pole cell migration in the Drosophila embryo
Pole cells attach to the endoderm and move through the foregut. A combination of chemoattractive and repulsive cues drive the PGCs and gonad precursor cells together and to a specific destination (the gonad). The PGCs divide through the larval stage and differentiate at metamorphosis. In the ovaries, the cells attach to stromal cap whereas in the testes, the cells attach to hub cells
Describe how germ cells migrate in Xenopus embryos
Once convergent extension has happened, the primitive gut is formed from the archenteron. PGCs then migrate into the posterior part of the developing gut, before leaving the gut to migrate to the gonads. Roughly 30 PGCs reach gonads governed by a fibronectin pathway and a crucial contribution by the Sdf-1 chemoattractant
In mammals, the primordial germ cells stay out of the embryo (in the extraembryonic territory) while the major inductive events occur, T or F
T
Once they have migrated anteriorly through the foregut what happens to the PGCs
They leave the gut and move to the protective niche of the gonads via the dorsal mesentery, entering the genital ridges
What is the role of support cells in PGC migration in mammalian embryos
Support cells travel with the PGCs to maintain the undifferentiated stem cell phenotype by secreting stem cell factor (SCF)
Teratomas are tumours seen in some foetuses, what are these and how do they form
Teratomas are an embryonic cancer that contains over-proliferative cells derived from all three germ layers. They are caused by a failure of the PGCs to migrate to the protective niche/failure or to make SCF. This in turn causes the germ cells to differentiate without any organisation.
