Molecular and genetic characterization of the <i>Drosophila morgue</i> gene
The Drosophila morgue gene was identified as a regulator of programmed cell death and encodes a novel ubiquitination (Ub) protein. Morgue protein contains a distinct combination of functional domains including: a zinc finger, F box, and variant Ub E2 conjugase domain. This unique combination suggests that Morgue may influence protein ubiquitination and targeting to the 26S proteasome for degradation. Morgue has been shown to promote turnover of a conserved anti-apoptotic protein, DIAP1. In the first part of this study, I present a published paper that describes the isolation and initial analysis of morgue.
In the second part of this thesis, I present a published review that discusses different models for Morgue function and describes the identification of a morgue orthologue in mosquito, Anopheles gambiae. This study compares the architecture of the two Morgue proteins, as the F box and conjugase domain within the two proteins are located in similar positions, and the F box and conjugase domains of AgMorgue exhibit 54% and 66% amino acid sequence identity to Morgue. Interestingly, the glycine substitution for the active site cysteine in AgMorgue is conserved. A zinc finger motif located at the NH2-terminus was also identified in both Morgue proteins.
In the third part of this study, I performed additional P-element excision screens to generate specific loss-of-function morgue alleles. Several viable alleles were obtained; however, the mutants appeared weak and were shown to exhibit decreased locomotor capabilities in adult climbing assays. Analysis of mutant embryos using a number of cell-type specific markers revealed partially penetrant disruptions in the number, position, and morphology of specific neurons and glia in both the central and peripheral nervous system.
Lastly, I describe strong genetic interactions between morgue mutants and mutations in the effete gene, which encodes a conserved Ub E2 conjugase that also influences DIAP1 levels and programmed cell death. Thus, in contrast to either morgue or effete mutants alone, animals homozygous for mutations in both these genes exhibit major disruptions in life cycle progression as they arrest in the third instar larval stage. These mutant larvae come to exhibit several morphological and anatomical abnormalities.