, 2004 and Witsell et al., 2009). Minos elements have very little insertional bias, transpose stably,

and efficiently ( Metaxakis et al., 2005, Bellen et al., 2011 and Venken et al., 2011), and excise imprecisely ( Metaxakis et al., 2005 and Witsell et al., 2009). The percentage and overall size of imprecise excisions for P elements and Minos can be increased when performed in a mus309 mutant KU-57788 datasheet background ( Witsell et al., 2009). Deletions are true null alleles of genes. Deletions can be generated through X-ray mutagenesis, imprecise excision of a P element or Minos (see above), excision of sequence between any two P element transposons located at different positions of the same chromosome ( Cooley et al., 1990, Parks et al., 2004 and Paré et al., Selisistat mouse 2009), the deletion-generator strategy ( Huet et al., 2002,

Mohr and Gelbart, 2002 and Myrick et al., 2009), or Flp-mediated recombination between two FRT sites each located in a transposon located at different positions of the same chromosome ( Ryder et al., 2004, Ryder et al., 2007, Parks et al., 2004 and Cook et al., 2010a). FRT deletions now cover 98% of the chromosomes ( Cook et al., 2010b). These stocks are the most widely used stocks in the fly community as they permit mapping of mutations through complementation tests. RNAi is the simplest way to affect gene function quantitatively. First performed through embryonic microinjections (Kennerdell and Carthew, 1998), RNAi was demonstrated in vivo using the GAL4/UAS system ( Fortier and Belote, 2000, Lam and Thummel, 2000 and Kennerdell and Carthew, 2000). Four genome-wide RNAi libraries aimed at targeting all fly genes have been or are being generated. The first library, encompassing 22,270 lines covering 88% of all the predicted protein-coding genes, was generated

in a P element ( Dietzl et al., 2007). The addition of the Dicer-2 enzyme improved knockdown levels for RNAi transgenes that generally resulted in a hypomorphic phenotype ( Dietzl Terminal deoxynucleotidyl transferase et al., 2007), although introduction of Dicer-2 may lead to toxicity. In the neurobiology field, this library has been used to screen for Notch signaling components during external sensory organ development ( Mummery-Widmer et al., 2009), heat nociception ( Neely et al., 2010), and stem cell renewal ( Neumüller et al., 2011). Particularly elegant uses of RNAi lead to the identification of Sex Peptide receptor and the neurons that respond to it ( Yapici et al., 2008 and Häsemeyer et al., 2009). A second library consisting of 11,496 lines covering 6,047 genes was generated in a P element as well and was used to identify novel components involved in the circadian clock network ( Matsumoto et al., 2007) (R. Ueda, personal communication). Unfortunately, since the integration site of P elements cannot be controlled, position effects result in variable knockdown.