(D) Quantification of electron microscopy imaging. Three independent experiments were quantified. Mitochondria were counted (cWT n = 232, PEX3-/- n = 266, and PEX3-/-+ATAD1 n = 257) and binned into 3 categories: mitochondria with many cristae and low electron density (Type 1), mitochondria with fewer cristae (Type 2), and mitochondria with high electron density and/or almost no cristae (Type 3). 