The Lab in Action
Transgenic worms expressing a myo-3::lacZ transgene
(Click for full-scale image)
Here you see worms
magnified about 50X that are expressing an added gene, the gene that
encodes B-galactosidase. The expression of B-galactosidase is controlled
by a promoter (on/off switch) from the myo-3 gene. We have exposed the
worms to a substrate of the B-galactosidase enzyme; this substrate turns
blue only in the presence of the enzyme. This way you can see exactly
which cells of the animal have ‘turned on’ the gene because the animal
is transparent. This is a way of asking which cells normally express the
myo-3 gene. In this case, the protein also contains a nuclear
localization signal, so only the nucleus of each of the myo-3 expressing
cells is blue. The large worm is oriented with anterior to the bottom,
so you can see that only about 13 cells in the head end are expressing
myo-3. You can also see that myo-3 expression is constant in
developmental time - both young and old larvae and adults have the same
pattern of blue dots. This is a very powerful technique used to figure
out the function of particular genes. Students in my molecular biology
course use sets of animals like this to learn about gene expression
patterns. Pretty Cool!!
Microinjection of Mutant DNA to Produce Transgenic Worms
(Click for full-scale image)
Isn’t this
awesome? Undergraduates in my lab have learned to make mutant genes and
do this microinjection technique. A single C. elegans worm is shown
magnified about 100X, with anterior to the left. (Notice that you can
see the internal organs – this is a transparent animal!) An injection
needle (we make these easily) is shown pushing into the cuticle and the
ovary of the animal. The ovary looks a bit like a dimpled golf ball –
each dimple is the nucleus of a developing oocyte. The next step will be
to poke the needle into the gonad and release some DNA into the ovary
where it will be taken up by some of the oocytes to produce transgenic
baby worms!
