The endogenous cno locus has been mutated so that the encoded protein lacks a conserved region of the FAB domain (amino acid residues 1937-2051 are missing) and is tagged at the C-terminal end with GFP. In addition, sequence containing 1. an attP site, 2. a loxP cassette containing a Disc\RFPDsRed(T1).3xP3.cHa marker is present downstream of the cno 3'UTR.