C. elegans

Question 1

Why C. elegans?

Answer 1

Small
Rapid life cycle
Non-parasitic
Transparent
Cell lineage is invariant

Question 2

Forward Genetics

Answer 2

A method to identify the genes that cause a specific phenotype
-begins by introducing random mutation into an organism’s genome, then screening the mutated population for individuals exhibiting a change.
-Genetic screen for Recessive Zygotic Mutants

Question 3

Hermaphrodites

Answer 3

• Produce both eggs and sperm, fertilization occurs within a single adult individual
• The egg becomes fertilized by rolling through a region of the adult worm (spermatheca) that contains mature sperm

Question 4

Males

Answer 4

-Occur every 1/600 when meiosis causes a y chomosome
-cross-fertilization can occur

Question 5

Role of sperm/centriole in A/P axis specification

Answer 5

The centrosome organizes microtubules which contacts oocyte’s cortical cytoplasm - pushes male pronucleus to nearest ent of the ooctye (posterior)
Sperm centrosome-organized microtubules prevent PAR-2 from from being phosphorylated, allowing it to bind to PAR-1 and enter the cortex

Question 6

A/P axis

Answer 6

Proteins are uniformly distributed - A/P is NOT set in the unfertilized egg

Question 7

AIR-1

Answer 7

Centrosome-associate protein breaks the symmetry
- Air-1 relocates from egg cortex and cytoplasm to sperm centrioles and promotes their maturation
- Air-1 phosphorylates targets in cortex that cause the collapse of the cortical actomyosin network

Question 8

Maternal Effect Gene

Answer 8

A gene whose product is made by the mother, but is required in the embryo for the early development to proceed normally
- mom makes and packages the RNA or protein
- the zygote’s phenotype depends on the mother’s genotype

Question 9

Asymmetry - A/P axis

Answer 9

Mitotic spindle is closer to the posterior, causing asymnetrical divisions
When posterior PARs occupy the cortex, symmetry is broken

Question 10

Germline silencing

Question 11

Mitotic spindle position

Answer 11

The Wnt signal leads to the phosphorylation of targets within the EMS cell that directly reorient the mitotic spindle. This reorientation ensures that the division plane is positioned asymmetrically, leading to the generation of daughter cells with distinct sizes and cytoplasmic contents. This process occurs independently of transcriptional changes.

Question 12

Protein presence and protein activity

Question 13

Cell intristic

Answer 13

Cell autonomous

Question 14

Cell extrinsic

Answer 14

Non-autonomous

Question 15

Competence

Answer 15

The ability of cells or tissues to respond to a specific inductive signal

Question 16

Necessary vs. Sufficient

Answer 16

Necessary
A condition that must be present for an event to occur.
Sufficient
A condition or set of conditions that will produce an event.

Question 17

Blastomere recombination experiments

Answer 17

Combining EMS with other AB cells results in No Gut. P2 is necessary for E specification.

Question 18

Non-canonical wnt signaling

Answer 18

Involves Wnt ligands and receptors but does not rely on β-catenin-mediated transcriptional activation. Instead, it often influences cell polarity, cytoskeletal rearrangements, and calcium signaling.

Question 19

GSK-3 roles

Answer 19

1. Phosphorylates the targets that reorient mitotic spindle in EMS
2. Activation WRM-1 which transmits signal asymmetrically to the E nucleus

Question 20

How wrm-1(B-cat) / pop-1(TCF) function is unique

Answer 20

WRM-1 is the b-cat for the non-canonical wnt pathway. It transmits the asymmetric signal that inhibits Pop-1 in the E nucleus which turns gut genes on.
When pop-1 is on (in MS nucleus) gut genes are inhibited.

Question 21

Laser ablation technique

Answer 21

Focusing a laser beam through a microscope lens to kill a single cell

Question 22

Equivalence Group

Answer 22

Cells that have the POTENTIAL to adopt the same fate. In c. elegans, all 6 VPCs (P3.p - P8.p) have the potential to adopt the fate induced by the anchor cell.

Question 23

Vulva Precursor Cells (VPCs)

Answer 23

Vulva precursor cells. Forms vulva

Question 24

1-2-3 degree fates

Answer 24

1 degree fate induced by anchor cell, forms vulva opening. 2 degree fate induced by a combination of graded signal and sequential signal

Question 25

Vul & Muv mutants

Answer 25

Vulvaless mutation, bag of worms
Multivulva, ectopic

Question 26

Graded signlaing mechanisms

Answer 26

An isolated VPC can become 1 or 2 and their fates are independent
Lin-3 action is concentration dependent
If P5.p was missing the Let-23 receptor, it would be 3

Question 27

Sequential signaling mechanisms

Answer 27

When P4.p and P7.p have no Lin-3 receptor, they still adopt 2 fates
If P5.p was missing the Let-23 receptor, it would be secondary

Question 28

Morphogen

Answer 28

Molecule that elicits different responses depending upon its concentration

Question 29

Lateral inhibition

Answer 29

When 1 cell adopts a fate, it prevents its neighbors from having that fate

Question 30

Notch/delta signaling pathway

Answer 30

Juxtacrine signaling. Primary cell telling secondary cell to be 2 not 1.
Both cells contain delta (ligand) and Lin-12 (notch)
Lin-3 signal from AC down regulates Lin-12 in P6.p

Question 31

Skn-1

Answer 31

A maternal effect gene that is required for EMS and sufficient for MS. present in EMS and P2. BE EMS!

Question 32

Pie-1

Answer 32

Zinc transcriptional repressor that maintains transcriptional silence in P2 and prevents SKN-1 from turning into EMS

Question 33

Lin-3/EGF

Answer 33

Signal given by the AC that specifies the primary cell

Question 34

let-23/EGFR

Answer 34

Acceptor for Lin-3

Question 35

Anchor cell

Answer 35

a specialized cell in the C. elegans gonad that plays a crucial role in inducing vulval development.

Question 36

lin-12

Answer 36

Notch type transmembrane receptor
- if we loose lin-12 we get all primary
- If we activate Lin-12 in all 6 cell, we get all secondary
Lin-12 is necessary and sufficient for secondary cell fate

Question 37

delta-like ligands