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Mosaic analysis in C. elegans
How are mosaic worms generated?
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Inject mixture of DNA carrying a cell autonomous marker (such as GFP) and DNA
carrying a wild type gene (extracromosomal element) into the gonads of a
hermaphrodite (P0) with a homozygous mutant background (figure A).
o Within the germline of the injected worm these pieces of DNA form stable minichromosomes containing the marker and the wild-type allele (the “array”)
(figure B)
Yochem & Herman, 2003
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Self the hermaphrodite and pick progeny (F1) with a wild type phenotype and that is
positive for the marker (such as an all-green worm if the marker is GFP). Why? You
want your worms in the next generation to start out fully wild type and positive for the
marker so that when they lose the aray, the cells will become negative for the marker,
and mutant.
o Although these worms have a wild type phenotype, they are still homozygous
mutant (figure B)
Self the phenotypically wild type F1’s
o In a small fraction of the F2 progeny, the array can be randomly lost via mitosis
in the developing worm.
 If one cell loses the array, all its progeny will no longer have the array,
and will therefore no longer have the wild type allele
Observe whether there are clones (groups of genotypically identical cells from the same
lineage) within your F2 progeny that have mitotically lost your array(figure C)
o The later in development you look, the larger your clones will be.
o The earlier in development your array is lost, the larger your clones will be.
o Would these clones be negative or positive for the marker? Negative
o Would these clones express the wild type gene? no
How are mosaic worms analyzed?

Mosaic analysis can be used to tell whether a gene acts cell autonomously or cell nonautonomously.
o If a gene acts cell autonomously, a mutation in that gene affects the cell in
which it is mutated.
 Clue that a gene is acting cell autonomously: a cell that has lost the array
has a mutant phenotype (Figure C)
o If a gene acts cell non-autonomously, a mutation in the gene within one cell
affects another cell that is not mutant.
 Clues that a gene is acting cell non-autonomously: a cell that hasn’t lost
the array has a mutant phenotype. (Figure D)
 Cell non-autonomy implicates what kind of interaction? Cell-cell
interaction
References:
Investigating C. elegans development through mosaic analysis, John Yochem and Robert K.
Herman, Development 130, 4761-4768 (2003)
http://www.wormbook.org/chapters/www_geneticmosaics/geneticmosaics.html#bib17