Lecture 26

Question 1

What is meant when we refer to early cells of the embryo as totipotent

Answer 1

They can give rise to any of the germ layers and subsequently any cell of the body

Question 2

Most of the early derivatives of the totipotent cells will remain as adult or tissue specific stem cells, T or F

Answer 2

F – most will differentiate to form the somatic cells of the body

Question 3

What is the name given to the set of cells set aside in an undifferentiated state that contribute to an individual during its lifetime

Answer 3

Tissue specific or adult stem cells

Question 4

Tissue specific stem cells are maintained throughout life due to their ability to self-renew, T or F

Answer 4

F – they are gradually depleted over time

Question 5

What are gonadal stem cells

Answer 5

Another type of specialised cells distinct from tissue specific stem cells that are set aside in an undifferentiated state for the next generation

Question 6

In some animals as well as all plants, somatic cells can readily form new organisms, T or F

Answer 6

T – whereas in many animals there is an early division between somatic and germ cells

Question 7

Generation of the germ cells is said to be a two-step process, what are the main stages in this process

Answer 7

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

Question 8

A germ cell is a plastic/totipotent cell type capable of undergoing mitosis, T or F

Answer 8

F – they are capable of undergoing meiosis

Question 9

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

Answer 9

Asymmetric cell division

Question 10

What cell lineage in C. elegans is responsible for giving rise to the germ cells, discuss this lineage

Answer 10

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

Question 11

What causes the process used to create 2 different daughter cells during cell division

Answer 11

Asymmetric cell division is caused by the asymmetric localisation of cytoplasmic determinants within a cell

Question 12

Describe how localisation of cytoplasmic determinants can both subsequently lead to both symmetrical and asymmetrical cell divisions

Answer 12

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

Question 13

What are the two daughters produced by asymmetric division in the formation of the germ line

Answer 13

One daughter cell will be maintained as a stem cell while the other will differentiation

Question 14

Give an example of P-granule determinant that becomes localised during the generation of the P-cell lineage during C.elegans development

Answer 14

PIE1 – a transcription blocker that also subsequently prevents differentiation

Question 15

Other than blocking transcription, what can other cytoplasmic determinants mediate in the P-cells

Answer 15

Translation blockers, promoters of stem fates, cause cells to undergo meiosis

Question 16

P-granules become restricted to one cell, this cells will be the germ cell, T or F

Answer 16

T

Question 17

What is the name of the region in the Drosophila embryo that is responsible for mediating germ line development

Answer 17

Germ plasm

Question 18

Germ line determination occurs during what process in the Drosophila embryo

Answer 18

Cellularisation

Question 19

Give an example of a specific gene product localised posteriorly in the Drosophila embryo

Answer 19

Germ cell-less

Question 20

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

Answer 20

Sterility

Question 21

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

Answer 21

Nanos

Question 22

The frog cells that inherit the gcl homologue will become the primordial germ cells, T or F

Answer 22

T

Question 23

What is different about the location where the PGCs are determined in mammalian embryos

Answer 23

In mammals, the primordial germ cells are determined outside of the main developing body axes at the junction of the epiblast/hypoblast

Question 24

What sort of signals must the PCGs in mammalian embryos be prevented from receiving in order to maintain their stem capability

Answer 24

Signals that govern formation of the body axes such as wnts, FGFs, BMPs, Hedgehog and RA

Question 25

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

Answer 25

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.

Question 26

What is meant when referring to the gonads as a protective niche

Answer 26

The gonad regions are a specialised protective microenvironment that prevent the PGCs from differentiating

Question 27

Describe pole cell migration in the Drosophila embryo

Answer 27

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

Question 28

Describe how germ cells migrate in Xenopus embryos

Answer 28

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

Question 29

In mammals, the primordial germ cells stay out of the embryo (in the extraembryonic territory) while the major inductive events occur, T or F

Answer 29

T

Question 30

Once they have migrated anteriorly through the foregut what happens to the PGCs

Answer 30

They leave the gut and move to the protective niche of the gonads via the dorsal mesentery, entering the genital ridges

Question 31

What is the role of support cells in PGC migration in mammalian embryos

Answer 31

Support cells travel with the PGCs to maintain the undifferentiated stem cell phenotype by secreting stem cell factor (SCF)

Question 32

Teratomas are tumours seen in some foetuses, what are these and how do they form

Answer 32

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.