Investigating the function of MACPF proteins using Drosophila melanogaster

2017-02-07T03:25:17Z (GMT) by Lauren Forbes-Beadle
The membrane attack complex/perforin-like (MACPF) protein superfamily contains members found within all kingdoms of life. Many MACPF proteins play important roles in mammalian immunity because of their inherent ability to insert into cell membranes and form pores. The complement proteins of the membrane attack complex and the perforin protein are well characterised MACPF proteins involved in immunity that have the ability to form pores. Not all MACPF proteins form pores however, and many have functions in development. These developmental roles are less well understood, and in addition many MACPF proteins have unknown functions. <br>     <br>    To address this, here the <i>Drosophila </i>model system has been utilised to investigate the in vivo roles of a number of MACPF proteins. Torso-like is the sole <i>Drosophila </i>MACPF protein and functions in embryonic development in the terminal patterning pathway. This pathway controls the specification of the anterior and posterior termini of the developing embryo. This thesis first aimed to determine if and how Tsl acts in <i>Drosophila</i> immunity, and if this function is similar to mammalian MACPF proteins that function in the immune response. By infecting a <i>tsl</i> null mutant with a range of pathogens, it was found that Tsl is required for the <i>Drosophila</i> immune response. Unexpectedly <i>tsl</i> null mutants had a reduced number of immune cells indicating that Tsl may be required for the development of these cells rather than acting as an immune effector. <br>     <br>    Secondly, to further understand how Tsl functions, MACPF proteins from distinct organisms such as mammals and the sea urchin were expressed in <i>Drosophila</i> to determine if they could functionally replace Tsl. This method was also used to discover novel functions for MACPF proteins by utilising the functional conservation of many biological pathways between <i>Drosophila</i> and other organisms. The MACPF proteins tested could not replace the function of Tsl in terminal patterning of the embryo. Unexpectedly however, a novel function in the Notch pathway was uncovered for two distantly related MACPF proteins, the protein Mpeg1 and the sea urchin protein Apextrin. <br>     <br>    Overall this thesis demonstrates the diverse developmental roles of MACPF proteins and highlights the utility of using <i>Drosophila</i> as a model system to investigate gene function. Due to the evolutionary conservation of important signalling pathways, the study of MACPF proteins in <i>Drosophila</i> provides significant insight into the function of MACPF proteins in new developmental roles. The possible cellular effects of MACPF proteins are discussed in relation to these novel findings.