Transgenesis in C. elegans - Caenorhabditis Elegans: Molecular Genetics and Development - page 179

appropriately constructed transgene or RNAi construct. Once a toolbox of these
strains has been created, it could be used by anyone in the community who requires a
specific expression pattern for their gene of interest. Another exciting possibility is
that the FLP recombinase system, which has been used to induce gene expression
( Davis et al., 2008; Voutev and Hubbard, 2008 ), could be used for tissue-specific
elimination of gene expression. This seems a likely future development, given that
single-gene insertions and homologous recombination techniques have been devel-
oped ( Frokjaer-Jensen et al., 2008; Vazquez-Manrique et al., 2010 ).
Avariation on mosaic analysis that would be useful for researchers is a technique
that permits tissue- or spatially restricted knockdown of gene activity for use in a
genetic screen. This technique is crucial for any researcher studying a process that
requires genes essential at earlier developmental time points or for other processes.
Emerging techniques that restrict RNAi sensitivity to a small set of cells or to
specific developmental stages could, in theory, permit these types of genomewide
screens ( Calixto et al., 2010; Qadota et al., 2007 ).
Another technology emerging in other systems that may have applications in
C. elegans is the use of zinc finger nucleases. These are heterodimers consisting
of engineered C 2 H 2 zinc finger arrays expressed as fusions to the nuclease domain of
the restriction enzyme Fo kI( Kim et al., 2010 ). These enzymes are capable of single
site-specific cleavage of DNA, which in theory can result, as with transposon
excision, in imprecise repair of the break (i.e., generating a mutation) or incorpo-
ration of sequences from a transgene repair template. At least one such enzyme has
been found to function somatically in C. elegans ( Carroll et al., 2008; Morton et al.,
2006 ), raising the hope that if germ-line expression can be achieved, it may be
possible to cause germ-line site-specific chromosome modification.
VI. Summary
The creation of transgenic strains is one of the most important tools for analysis of
gene function. Two different delivery methods for C. elegans transgenesis, micro-
injection and microparticle bombardment, have been developed. From these basic
methods, a plethora of techniques have emerged that permit analysis of gene expres-
sion and function in a range of key cellular and developmental processes. The future
holds promise for even greater precision and sophistication in experimentally
manipulating gene expression in C. elegans.
References
Bacaj, T., and Shaham, S. (2007). Temporal control of cell-specific transgene expression in
Caenorhabditis elegans. Genetics 176, 2651-2655.
Bazopoulou, D., and Tavernarakis, N. (2009). The NemaGENETAG initiative: Large scale transposon
insertion gene-tagging in Caenorhabditis elegans. Genetica 137, 39-46.