The role ofPeroxin 7duringDrosophilaembryonic development

Abstract

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.

Rosy Beginnings: Studying Peroxisomes in Drosophila

“…A clue for Pex7 activity in Drosophila may come from its pattern of expression. Compared to the relatively ubiquitous expression of Drosophila Pex genes in the early embryo Pex7 is expressed at relatively high levels in only a small subset of cells thought to be of neural lineage (Pridie and Simmonds, 2020). This suggests a more specialized, potentially cell-lineage specific role.…”

“…There seems to be a varied phenotypic spectrum associated with mutations in Pex and other peroxisome-linked genes during development. The mRNA encoding most Pex genes is expressed ubiquitously during early embryo development, although some (Pex7, Pex13, Pex14, Pex19) display differences in relative mRNA levels between various cell lineages (Leader et al, 2018;Pridie and Simmonds, 2020). However, likely due to a large maternal contribution of peroxisomes, fly embryos develop into larvae even when homozygous for most Pex gene mutations.…”

“…An insertional mutation of Pex5 is lethal at or before pupariation with increased cell death. Pex7 mutants are viable (Di Cara et al, 2019;Pridie and Simmonds, 2020). Mutations of genes encoding proteins of the importomer Pex2, Pex10 and Pex12 are viable but are associated with sterility phenotypes.…”