Novel mechanisms for the regulation of zinc homeostasis in Drosophila melanogaster

2017-03-01T00:23:23Z (GMT) by Richards, Christopher Dean
Zinc is an essential metal and is required for a plethora of cellular and physiological processes. Highlighting its essential role in biology are predictions that up to 10% of the human genome encodes proteins with zinc binding domains. The maintenance of zinc homeostasis at a cellular level is largely controlled by two interacting protein families, the ZIP (SCL39) family responsible for zinc uptake into the cytosol and the ZnT (SCL30) family responsible for zinc efflux out of the cytosol. The large number of transporters in Drosophila (17) and mammalian (24) transporters leads to difficulties determining the function of single genes, therefore the basic functional role of many of these transporters remains largely unknown. Utilising the powerful genetic tools available in Drosophila melanogaster this study aimed to build upon previous work conducted in the Burke laboratory and perform a detailed functional analysis of two highly conserved Drosophila dZIP genes, dZIP89B and dZIP88E. These transporters share high amino acid conservation with dZIP42C.1 and dZIP42C.2 which have roles in dietary zinc uptake, and provide an excellent system in which to explore the potential for functional redundancy and specificity within the Drosophila zinc transport system. Here, I provide detailed analysis of genetic interactions, mRNA and protein expression patterns, systemic/localised zinc status and a detailed characterisation of null mutants in these genes that suggests functionally specific roles for dZIP89B and dZIP88E. My results suggest that dIZP89B may be a low affinity, constitutively active transporter involved in dietary zinc uptake, indicating this process may be more sophisticated than previously suggested. I also provide evidence for the novel role of dZIP88E in the regulation of systemic zinc status, a mechanism that has not yet been described in mammalian or insect systems. Furthermore, two genetic modifier screens utilising chromosomal deficiency lines and targeted RNAi suppression in combination with a sensitised zinc toxicity background were carried out to identify novel regulators of zinc homeostasis. The results of these screens not only provide an excellent platform for further research novel genes that interact with the zinc homeostasis machinery, but validate the use of Drosophila for screens of this nature.