Three-dimensional reconstruction of a peroxisomal reticulum in regenerating rat liver: Evidence of interconnections between heterogeneous segments

Abstract

The three-dimensional (3-D) form and the interrelationship of peroxisomes (Po) in the model of regenerating rat liver after partial hepatectomy were studied by computer-assisted 3-D reconstruction of serial ultrathin sections. Po were labeled cytochemically for either catalase, which stains them all uniformly, or for D-amino oxidase (DAA-OX), which gives a heterogeneous reaction with lightly and darkly stained PO. In regenerating rat liver, Po exhibit marked pleomorphism with some budding forms and dumbbellshaped ones. The 3-D reconstruction revealed many single spherical Po measuring 0.15-0.8 μm in diameter. In addition, two to five Po were found interconnected with each other via narrow 30-50-nm hourglass-shaped bridges forming a reticulum. Such aggregates of Po measured 1.5-2.5 μm across. Whereas all segments of this reticulum stained homogeneously for catalase, they exhibited a marked difference in the intensity of the DAA-OX reaction. These observations are consistent with the view of peroxisomal proliferation by budding or fragmentation from preexisting ones. Under such conditions of rapid growth as in regenerating liver, Po may be interconnected forming a reticulum. The interconnections between Po with differing DAA-OX activities suggest that they originate from the same parent organelle.