Cloning of the neurodegeneration genedrop-deadand characterization of additional phenotypes of its mutation

Abstract

Mutations in the Drosophila gene drop-dead (drd) result in early adult lethality and neurodegeneration, but the molecular identity of the drd gene and its mechanism of action are not known. This paper describes the characterization of a new X-linked recessive adult-lethal mutation, originally called lot’s wife (lwf1) but subsequently identified as an allele of drd (drdlwf); drdlwf mutants die within two weeks of eclosion. Through mapping and complementation, the drd gene has been identified as CG33968, which encodes a putative integral membrane protein of unknown function. The drdlwf allele is associated with a nonsense mutation that eliminates nearly 80% of the CG33968 gene product; mutations in the same gene were also found in two previously described drd alleles. Characterization of drdlwf flies revealed additional phenotypes of drd, most notably, defects in food processing by the digestive system and in oogenesis. Mutant flies store significantly more food in their crops and defecate less than wild-type flies, suggesting that normal transfer of ingested food from the crop into the midgut is dependent upon the DRD gene product. The defect in oogenesis results in the sterility of homozygous mutant females and is associated with a reduction in the number of vitellogenic egg chambers. The disruption in vitellogenesis is far more severe than that seen in starved flies and so is unlikely to be a secondary consequence of the digestive phenotype. This study demonstrates that mutation of the drd gene CG33968 results in a complex phenotype affecting multiple physiological systems within the fly.

Defective gut function in drop-dead mutant Drosophila

“…1b). This result is consistent with our previous finding that defecation rates in mutant flies are severely reduced but not eliminated (Blumenthal, 2008). …”

“…In previous work (Blumenthal, 2008), we observed variability in the crop volumes of the mutants and had speculated that those flies with small crops might be the most severely affected and be too weak to feed. Our current data are consistent with this interpretation.…”

“…We have previously reported that mutation of the Drosophila gene drd appears to cause a defect in the movement of food through the gut (Blumenthal, 2008). The drd gene encodes a large protein with multiple hydrophobic, presumably membrane-spanning, domains; the function of this protein and its pattern of expression are currently unknown.…”

“…Severe brain degeneration has been reported in mutant flies after the appearance of the motor defects (Benzer, 1971; Buchanan and Benzer, 1993). We have reported that, in addition to these phenotypes, drd mutant flies also show increased crop volumes and reduced rates of defecation; both of these phenotypes are evident during the first two days post-eclosion, before any of the flies have begun to die (Blumenthal, 2008). While mutation or misexpression of specific genes has been shown to affect feeding behavior in larval Drosophila (Lee and Park, 2004; Melcher and Pankratz, 2005; Wu et al, 2003; Wu et al, 2005), this was the first example of a mutation that altered food processing or digestive function in the adult.…”

The functional organisation of glia in the adult brain of Drosophila and other insects

“…As flies age the brain begins to degenerate (Buchanan and Benzer, 1993) and an acceleration of age related markers suggests that theses flies age more rapidly (Rogina et al , 1997). While the early onset mortality phenotype of drop dead may in part result from digestive abnormalities (Blumenthal, 2008), the aberrant shape of glia in the adult suggests rather obviously a role for proper glial development in the maintenance of nervous system function and neuronal survival (Buchanan and Benzer, 1993). …”