Research using the fruit fly Drosophila melanogaster has traditionally focused on understanding how mutations affecting gene regulation or function affect processes linked to animal development. Accordingly, flies have become an essential foundation of modern medical research through repeated contributions to our fundamental understanding of how their homologs of human genes function. Peroxisomes are organelles that metabolize lipids and reactive oxygen species like peroxides. However, despite clear linkage of mutations in human genes affecting peroxisomes to developmental defects, for many years fly models were conspicuously absent from the study of peroxisomes. Now, the few early studies linking the Rosy eye color phenotype to peroxisomes in flies have been joined by a growing body of research establishing novel roles for peroxisomes during the development or function of specific tissues or cell types. Similarly, unique properties of cultured fly Schneider 2 cells have advanced our understanding of how peroxisomes move on the cytoskeleton. Here, we profile how those past and more recent Drosophila studies started to link specific effects of peroxisome dysfunction to organ development and highlight the utility of flies as a model for human peroxisomal diseases. We also identify key differences in the function and proliferation of fly peroxisomes compared to yeast or mammals. Finally, we discuss the future of the fly model system for peroxisome research including new techniques that should support identification of additional tissue specific regulation of and roles for peroxisomes.

Peroxisomes are organelles in eukaryotic cells responsible for processing several types of lipids and management of reactive oxygen species. A conserved family of peroxisome biogenesis (Peroxin, Pex) genes encode proteins essential to peroxisome biogenesis or function. In yeast and mammals, PEROXIN7 (PEX7) acts as a cytosolic receptor protein that targets enzymes containing a peroxisome targeting signal 2 (PTS2) motif for peroxisome matrix import. The PTS2 motif is not present in the Drosophila melanogaster homologs of these enzymes. However, the fly genome contains a Pex7 gene (CG6486) that is very similar to yeast and human PEX7. We find that Pex7 is expressed in tissue-specific patterns analogous to differentiating neuroblasts in D. melanogaster embryos. This is correlated with a requirement for Pex7 in this cell lineage as targeted somatic Pex7 knockout in embryonic neuroblasts reduced survival. We also found that Pex7 over-expression in the same cell lineages caused lethality during the larval stage. Targeted somatic over-expression of a Pex7 transgene in neuroblasts of Pex7 homozygous null mutants resulted in a semi-lethal phenotype similar to targeted Pex7 knockout. These findings suggest that D. melanogaster has tissue-specific requirements for Pex7 during embryo development.

Running title: Drosophila melanogaster Pex7Abstract Peroxisomes are organelles responsible for aspects of lipid metabolism and management of reactive oxygen species. Peroxisome Biogenesis Factor (Peroxin, Pex) genes encode proteins essential to peroxisome biogenesis or function. In yeast and mammals, PEROXIN7 acts as a cytosolic receptor protein that targets a subset of enzymes for peroxisome matrix import.Proteins targeted by PEROXIN7 contain a peroxisome targeting sequence 2 (PTS2) motif. The PTS2 was not found in the D. melanogaster homologs of proteins that are PEROXIN7 targets in yeast or mammals, however comparative genomics suggest a Pex7 homolog is present in the D.melanogaster genome. Herein we report novel, tissue-specific patterns for transcription and translation of Pex7 in the D. melanogaster embryo that appear to be strongest in presumptive neuronal lineages. We also show that targeted somatic Pex7 knockout in neural precursors via targeted somatic CRISPR knockout affected survival of mutant embryos. Pex7 over-expression via Gal4-UAS also reduced adult survival but was not deleterious at the embryo stage. Notably, targeted somatic rescue of Pex7 in the neural precursors of Pex7 homozygous mutants also impaired embryo survival. We conclude that D. melanogaster has tissue-specific developmental requirements of Pex7 expression. This may be related to the requirement for peroxisomemediated lipid synthesis in cells of the central nervous system. Baron et al., 2016). Together, these data suggest that D. melanogaster Pex7 function is required for normal development of a specific subset of cells, likely of neuronal lineage. Materials and Methods Drosophila stocks, embryo collection and viability assays

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