Expression of the drosophila gene disconnected using the UAS/GAL4 system.

Abstract

The Drosophila disconnected (disco) gene encodes a transcription factor containing two C2H2 zinc-fingers that functions in the development of both embryonic and adult structures. The disco gene was initially identified from a mutation in which adult photoreceptor axons fail to connect with their target cells in the larval optic lobe (Steller et al., 1987). The optic lobes of disco mutants are poorly developed and lack optic lobe neurons, including the lateral neurons. Abnormal circadian rhythmicity has been attributed to the absence or aberrant differentiation of these lateral neurons (Hardin et al., 1992; Helfrich-Forster et al., 1998). Additionally, disco mutants show defects in thoracic and abdominal sensory axon development (Glossop and Shepherd, 1998). More recently, disco was found to have a broader role in embryonic pattern formation, functioning as a cofactor for the Hox proteins Deformed (Dfd) and Sex Combs Reduced (Scr) in the gnathocephalic segments (mandibular, maxillary, and labial); this more extensive role was masked by the partially redundant gene, disco-related (disco-r) (Mahaffey et al., 2001). Lack of both Disco and Disco-r causes embryonic lethality and the absence of some larval mouth structures arising from the gnathocephalic segments. The disco gene is also expressed in the antennal and leg imaginal discs and likely has a role in the development of these structures (Lee et al., 1991). The disco gene is located in region 14B of the X chromosome and consists of two exons separated by a single intron. The first exon is untranslated and comprises the majority of the disco 5 UTR. The second exon contains the complete open reading frame (ORF) encoding the 568 amino acid protein. The two C2H2 zinc finger regions, defining the DNA binding domain, are located between amino acids 89 and 149 (Heilig et al., 1991). As tools for further study of Disco function, we generated three UAS-disco constructs—two encoding wildtype proteins and one producing an altered protein like that encoded by the disco null allele. The UAS-disco wild-type construct was generated by the sequential insertion of two disco fragments into the Drosophila transformation vector pUAST (Brand and Perrimon, 1993). A 1,270-bp BglII-XbaI fragment representing the majority of the disco ORF (a subclone from 542.2; Surdej et al., 1990) was inserted into BglII-XbaI digested pUAST. Next, a 473-bp fragment, with an artificial EcoRI site immediately upstream of the initiation codon, was obtained by an EcoRI-BglII digestion of a 1,276-bp PCR product generated with the following primers: Forward primer, 5 GGA TCC GAATTC ATG GAG CAC ATA ATG 3 ; Reverse Primer, 5 ATG TAG GCA CTG TCG CTA TCC 3 . This fragment was inserted into the EcoRI-BglII sites of the initial BglII-XbaI pUAST construct. The final construct includes a 1,743-bp EcoRI-XbaI insert encoding the entire disco ORF with some 3 UTR. The second wild-type construct (further referred to as UAS-disco) and the mutant construct (further referred to as UAS-disco) were generated by PCR amplification of genomic DNA. A 1,704-bp fragment containing the complete disco ORF was generated using primers containing EcoRI sites: Forward primer, 5 CCC ACC ACA GAATTC ATG GAG CAC 3 ; Reverse Primer, 5 CCA TGG ATC GAATTC TGG ACA TTA 3 . After EcoRI digestion, the resulting PCR product was inserted into an EcoRI digested pUAST. For the UAS-disco construct, Oregon R genomic DNA was used as a template, while homozygous disco genomic DNA was used as a template for the mutant UAS-disco construct. This form of the protein contains a single amino acid change— Cysteine 127 is substituted with a Serine—which disrupts the first zinc finger. Prior analysis indicated that this mutant form of the Disco protein is nonfunctional (Heilig et al., 1991; Mahaffey et al., 2001). The sequence and reading frame of all constructs were verified by DNA sequence analysis. Integration of UAS-disco constructs into the Drosophila genome was carried out using P-element-mediated germ-line transformation essentially as described by Rubin and Spradling (1982). Two UAS-disco lines were obtained—a heterozygous line carrying UAS-disco on the second chromosome balanced over CyO (UAS-disco(II)), and a homozygous line with the insert on the