C. elegans Flashcards
Why C. elegans?
Small
Rapid life cycle
Non-parasitic
Transparent
Cell lineage is invariant
Forward Genetics
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
Hermaphrodites
- 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
Males
-Occur every 1/600 when meiosis causes a y chomosome
-cross-fertilization can occur
Role of sperm/centriole in A/P axis specification
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
A/P axis
Proteins are uniformly distributed - A/P is NOT set in the unfertilized egg
AIR-1
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
Maternal Effect Gene
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
Asymmetry - A/P axis
Mitotic spindle is closer to the posterior, causing asymnetrical divisions
When posterior PARs occupy the cortex, symmetry is broken
Germline silencing
Mitotic spindle position
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.
Protein presence and protein activity
Cell intristic
Cell autonomous
Cell extrinsic
Non-autonomous
Competence
The ability of cells or tissues to respond to a specific inductive signal
Necessary vs. Sufficient
Necessary
A condition that must be present for an event to occur.
Sufficient
A condition or set of conditions that will produce an event.
Blastomere recombination experiments
Combining EMS with other AB cells results in No Gut. P2 is necessary for E specification.
Non-canonical wnt signaling
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.
GSK-3 roles
- Phosphorylates the targets that reorient mitotic spindle in EMS
- Activation WRM-1 which transmits signal asymmetrically to the E nucleus
How wrm-1(B-cat) / pop-1(TCF) function is unique
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.
Laser ablation technique
Focusing a laser beam through a microscope lens to kill a single cell
Equivalence Group
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.
Vulva Precursor Cells (VPCs)
Vulva precursor cells. Forms vulva
1-2-3 degree fates
1 degree fate induced by anchor cell, forms vulva opening. 2 degree fate induced by a combination of graded signal and sequential signal
Vul & Muv mutants
Vulvaless mutation, bag of worms
Multivulva, ectopic
Graded signlaing mechanisms
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
Sequential signaling mechanisms
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
Morphogen
Molecule that elicits different responses depending upon its concentration
Lateral inhibition
When 1 cell adopts a fate, it prevents its neighbors from having that fate
Notch/delta signaling pathway
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
Skn-1
A maternal effect gene that is required for EMS and sufficient for MS. present in EMS and P2. BE EMS!
Pie-1
Zinc transcriptional repressor that maintains transcriptional silence in P2 and prevents SKN-1 from turning into EMS
Lin-3/EGF
Signal given by the AC that specifies the primary cell
let-23/EGFR
Acceptor for Lin-3
Anchor cell
a specialized cell in the C. elegans gonad that plays a crucial role in inducing vulval development.
lin-12
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
delta-like ligands
