C. elegans Larval development Flashcards
In which phases of C. elegans development do cell divisions happen?
during molting
What is the dauer stage?
if at L1 stage the larvae does not get enough food, it progresses to dauer stage instead of L2
dauer is isolated from tough environmental conditions
heat resistant
mouth sealed with a piece of cuticle
germline development is arrested
muscle, intestine and hypodermal cells shrink, the worm radially constricts
great form for dispersion (waiting for passing organisms to come by)
tend to look like toothpicks
when food is available again, they progress to L4 stage
can be induced by dauer pheromone
Heterochrony?
differences in relative timing of developmental events
What is a specific developmental stage marker in adult worms?
alae
adult specific ridges in the cuticle
Which 2 phenotypes do you observe if you mutate lin-14?
semidominant: retarded mutation
- lin-14 hyperactive
- reiteration of L1 stage
- single layered cuticle, no alae
recessive: precocious
- loss of function
- skips L1, goes to L2 straight away
- makes alae twice
Which lin genes control the timing of specific postembryonic developmental events?
4, 14, 28, 29
What is the role of lin-4 and let-7 (sisters) genes?
encode miRNAs (cca 20nt)
miRNAs bind to 3’UTR regions of other genes and prevent their expression
What is the role and composition of the dauer pheromone?
dauer pheromone makes worms enter dauer stage even in presence of food
it is a mixture of ascarosides = sugars conjugated with lipids that bind and signal via GPCRs
ascarosides inhibit guanylyl cyclase
= inhibit GPCR signaling which would lead to growth because it signals presence of food
(in absence of food, also TGF-b and insulin are low)
When looking for mutants in receptors for the dauer pheromone, which phenotypes do you encounter?
daf-d = dauer defective daf-c = constitutive dauer
Which neurons are involved in ascaroside sensing?
amphid neurons
exposed in dauers too, despite the cuticle over mouth
What can daf-c phenotype result from?
disturbances in GPCR signaling (overexpression of G proteins, loss of funciton of guanylyl cyclase or cGMP gated channel subunits)
mutations in insulin-signaling pathways
mutations in TGF-B pathways
What is the response to low ascaroside levels?
amphid neurons release insulin and TGF-beta
they lead to de-repression of:
- daf-9 in the XXX cells (hormone producing cells in the head)
- daf-46 in the intestine
–> leads to dafachronic acid production
DA is diffusible steroid hormone
activates nuclear hormone expression of genes involved in growth (daf-12)
–> reproductive state
What is the relationship between daf-12 and let-7?
daf-12 regulates let-7
(feedback loop)
presence or absence of dafachronic acid stabilizes either adult or dauer stage
