Theoretically perfect model organism
• Well characterized life cycle-all stages easily accessible.
• Well characterized genetic system. • Well characterized genome-basically
sequenced and annotated.• The ability to reintroduce DNA into the
organism-transgenesis.• Closely related to humans-funding purposes.
Caenorabditis elegans• Life cycle: short 3 1/2 days, transparent
organism, complete cell lineage known.
• Genetic system: both classical and RNAi
• Genome: first metazoan sequenced 1998
• Transgenesis: injection of DNA
• Related to humans?
Cell lineage
• Early divisions
• Lineage structure and nomenclature
• Cell death
• Repeated lineages
M.vlpaa
Key blast cells are given upper case letters
The progeny are named by adding lower caseletters indicating the division axis:a-anteriorp-posteriord-dorsalv-ventrall-leftr-right
M great great great grandmothM.v great great grandmotherM.vl great grandmotherM.vlp grandmother M.vlpa motherM.vlpaa daughter
Following the lineage
Cell death
AB.alaaaala
alaralal
l r
DEADNeuron in ring ganglion
Kalthoff Analysis of Biological Development
Induction
1
2
A cell or group of cells removedfrom a second cell
that directs the developmentalfate of a second cell or group ofcells.
Z1.ppp Z1.pppZ4.aaa Z4.aaa
Individual A Individual B
Anchor cell/ Ventral uterine cell equivalence group
AC ACVU VU
Z1.ppp Z1.pppZ4.aaa Z4.aaa
Experiment A Experiment B
Anchor cell/ Ventral uterine cell equivalence group
AC AC
Cell ablation experiment
Z1.ppp Z1.pppZ4.aaa Z4.aaa
Experiment A Experiment B
Anchor cell/ Ventral uterine cell equivalence group
AC AC
Cell ablation experiment
The remaining cell always becomes an AC.The AC fate is the 1° (primary) cell fate.
Mutagenesis and screens
P0young hermaphrodite
EMS
+/+ +/+ +/+ +/+ +/+ +/m +/+ +/+ ….. F1
self self
F2All wild-type
Males
X X hermaphroditeX O male
At a frequency of 1/1000, males arise due to nondisjunction of the X chromosome.
Complementation analysis
males m1/m1 X hermaphordites m2/m2
1. All males have mutant phenotype
2. All males are wild-type
Non complementation screen
male a+ m-/a+ m- X hermaphrodite a- m+/a- m+
EMS
MostWild-type
a- m+
a+ m-
Non complementation screen
male a+ m-/a+ m- X hermaphrodite a- m+/a- m+
EMS
MostWild-type
Somea-
a- m+
a+ m-
Non complementation screen
male a+ m-/a+ m- X hermaphrodite a- m+/a- m+
EMS
MostWild-type
Somea-
a- m+
a+ m-
a- m+
a- m+
Non complementation screen
male a+ m-/a+ m- X hermaphrodite a- m+/a- m+
EMS
MostWild-type
Somea-
a- m+
a+ m-
a- m+
a- m+
Rarem-
Non complementation screen
male a+ m-/a+ m- X hermaphrodite a- m+/a- m+
EMS
MostWild-type
Somea-
a- m+
a+ m-
a- m+
a- m+
Rarem-
a- m-new
a+ m-
Transgenesis
YFG
rollD
Look for rolling progeny F1
Look for rolling progeny in F2
Horvitz and Sternberg Nature 351, 535
Transgenesis
Nucleus of F2 rolling progeny
YFG rollDYFGYFG rollD rollD rollD
Large concatenated arrays that are stablely maintained.
RNAi inhibition of gene expression
1. RNAi discovered in C. elegans and plants.
2. Double stranded RNA results in the degradation of homologous mRNA.
3. Double stranded RNA can be fed to worms in the E. coli they eat.
4. Allows for the systematic inhibition of all 20,000 genes of C. elegans.