Constructing an adult-viable ogre mutant genotype.
Flies carrying the ogrejnl3 (Nicklas and Cline, 1983) allele are early-stage lethal in our hands, possibly due to unidentified lethals elsewhere in the genome. In order to generate adult viable ogre mutants for analysis we produced flies carrying the ogrejnl3 allele on one X chromosome and a deficiency, Df(1)Sxlbt (Nicklas and Cline, 1983), on its homologous partner. The ogre mutant genotype referred to in the "Innexins in the CNS" website section therefore refers to female animals of genotype:-
Df(1)Sxlbt / ogrejnl3
In the image above, the whole X chromosome is represented as a green line. The location of the ogre locus and the innexin gene cluster at chromosomal position 6E4 is shown as a blue bar (also contains the carmine locus). The approximate extent of the deletion on the Df(1)Sxlbt chromosome is shown as a red bar which extends between positions 6E1/2 to 7A6. The genes at position 6E4 encoding ogre, inx2 and inx7, along with their predicted mRNAs, are presented at the bottom of the image (courtesy of www.flybase.org). Obviously, in addition to ogre, the Df(1)Sxlbt deletion takes out a lot of genes including other innexins. The CNS phenotypes of Df(1)Sxlbt / ogrejnl3 flies could be partly due to genes within the deletion that are also defective on the ogrejnl3 carrying chromosome other than ogre itself. This seems unlikely as the adult phenotype is very similar to that reported for ogrelethal escapers (....small optic lobes, small and somewhat disorganised brain, no other external morphological defects) and the phenotype can be partially rescued by expressing UAS-ogre using the GAL4/UAS (Brand and Dormand, 1995) system (see images, Rescue of mushroom body glia, Optic lobe rescue). Some endogenous Ogre protein can be detected in the central nervous system of Df(1)Sxlbt / ogrejnl3 flies (Ogre protein in the ogre mutant). This is not surprising as Ogre is required to reach adulthood; putative null alleles are pharate lethal (Lipshitz and Kankel, 1985). It appears that the viable allele ogrejnl3 retains expression in putative perineurial cells, large cells surrounding the brain that may be a component of the blood-brain barrier (Carlson et al, 2000).