C. elegans Cell fate

Question 1

How are oocytes genearted in a hermaphrodite worm?

Answer 1

DTC divides mitotically
when cells far enough, start undergoing meiosis (transition zone)
in the loop, most cells undergo cell death
after loop, in proximal arm, cells are still in meiosis I = no division yet (sidenote: also no gene transcription yet so proteins in these cells are maternal)
eventually, oocytes detach from syncytium
before fertilization, nucleus moves away from spermatheka and nuclear membrane breaks down

Question 2

What is oocyte maturation?

Answer 2

resumption of meoisis and continuing through meiosis II stage

Question 3

How does C. elegans sperm cells looke like?

Answer 3

amoeboid
no flagellum
use MSP for motility

Question 4

Describe discovery of Spe genes.

Answer 4

Spe phenotype = can make sperm, but cannot fertilize; observable by seeing brown blobs on the plate

EMS mutagenesis
mutant sperm results in only 50 % carrying the mutation
(spermatocyte in meiosis: 1° spermatocyte is 2 cells wih 2n, next division forms 4 2° spermatocytes + residual body)
even though the genotype is mutant, sperm functions normally because no gene transcription/translation yet
can see phenotypes in F2
check if not oocyte the one that’s defective by crossing with WT males

Question 5

What effect does sperm have on the oocyte before fertilization?

Answer 5

promotes oocyte maturation
causes sheath cell contraction (ovulation)

signaling via MSP

Question 6

Describe MSP signaling pathway.

Answer 6

MSP has an extracellular domain with extracellular signaling function
the signals are transduced through CLR-1 receptor in muscle plasma membrane to cause ovulation

Question 7

What causes the onset of Ca wave in C. elegans oocyte after fertilization?

Answer 7

signaling through TRP-3 (Ca channel)

Ca comes in from extracellular space

Question 8

How are axis initially specified in C. elegans oocyte?

Answer 8

oocyte not polarize prior to fertiilzation

sperm entry side marks posterior site

Question 9

What is the phenotype of Par mutants?

Answer 9

first cell division is symmetric

P granules do not localize to the posterior cell like they should

Question 10

Which protein associates with the posterior cortex first and how?

Answer 10

PAR-2
localized to sperm entry site because it causes MTOC formation and maternal determination proteins are transported along the microtubules

Question 11

What follows PAR-2 localization to the posterior cortex?

Answer 11

inhibits PAR-3 posteriorly, so it accumulates in A part
PAR-1 localizes to P
leads to asymmetric positioning of P granules and cell fate determinants (e.g. SKN-1)

Question 12

Which genes act downstream of PARs?

Answer 12

MEX-5/6
ZIF-1
PIE-1

Question 13

Which organ was used to study cell fate and why?

Answer 13

Pharynx

made from 2 founder cells in the beginning of the development (AB, MS)

Question 14

What is the role of PIE-1? What kind of protein it is?

Answer 14

CCCH zinc finger protein
prevents transcripton of mRNA (blocks RNA pol II)
in germ cells, required for efficient expression of NOS-2 (no NOS-2 = germ cells stay away from somatic gonad)
active in posterior cells to prevent anterior fate (in P1-4)

Question 15

Which protein degrades PIE-1 and how?

Answer 15

ZIF-1

interacts with E3 ubiquitin ligase

Question 16

What is the role of SKN-1 and how are its levels regulated?

Answer 16

TF
triggers EMS cell fate, but present also in P2
PIE-1 prevents its expression in P2

Question 17

Which proteins play a crucial role in creating protein asymmetries while mRNA is evenly distributed?

Answer 17

MEX-5/6

Question 18

What is the role of MAX-5/6?

Answer 18

they are localized and active ANTERIORLY
inhibit posterior fate
MEX inhibit ZIF-1 inhibitors = passively activate ZIF-1
ZIF-1 inhibits PIE-1
no PIE = no SKN-1 inhibition
SKN-1 triggers EMS cell fate

Question 19

How is MEX-5/6 activity regulated?

Answer 19

it is inhibited posteriorly by PAR-1

Question 20

Which proteins are most important in cell-cell signalization about positioning of the cell in the embryo? What are they homologous to?

Answer 20

GLP-1 = Notch homolog
APX-1 = Delta homolog

Question 21

At which stages of development does Glp-1 signaling play a role?

Answer 21

4-cell stage

12-cell stage

Question 22

What is the role of Wnt singaling in devlopment?

Answer 22

Wnt specifies posterior cells
cells become A when Wnt blocked

also regulates orientations of cell divisions

Question 23

Example of cell that produces Wnt ligand during C. elegans development.

Answer 23

P2 = makes ligand

affects receptor on EMS (mom-2, Frizzled homolog)