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Peroxisomes are ubiquitous subcellular organelles, which are highly dynamic and display large plasticity in response to cellular and environmental conditions. Novel proteins and pathways that mediate and control peroxisome formation, growth, and division continue to be discovered, and the cellular machineries that act together to regulate peroxisome number and size are under active investigation. Here, advances in the field of peroxisomal dynamics and proliferation in mammals and yeast are reviewed. The authors address the signals, conditions, and proteins that affect, regulate, and control the number and size of this essential organelle, especially the components involved in the division of peroxisomes. Special emphasis is on the function of dynamin-related proteins (DRPs), on Fis1, a putative adaptor for DRPs, on the role of the Pex11 family of peroxisomal membrane proteins, and the cytoskeleton.

Marine mussels are used as bioindicators of water pollution in marine and estuarine environments in the so-called "Mussel Watch" programs because of their capacity to accumulate numerous organic xenobiotics including aromatic hydrocarbons. In this study, we have analyzed the effects of two xenobiotics [benzo(a)pyrene and the water accommodated fraction of a lubricant oil] and two typical (rodent) peroxisome proliferators (clofibrate and dioctyl phthalate) on structure and function of peroxisomes in digestive glands of mussels Mytilus galloprovincialis, either following water exposure (for 1, 7, and 21 days) or after direct injection through the adductor muscle (for 1 and 7 days). The activities of catalase (CAT), acyl-CoA oxidase (AOX), and D-amino acid oxidase were determined in whole homogenates of digestive glands. In addition, stereological methods were applied on sections stained histochemically for demonstration of catalase activity in order to quantify the morphological changes of peroxisomes. The peroxisomal acyl-CoA oxidase and D-amino acid oxidase were increased in mussels injected for 7 days with benzo(a)pyrene, phthalate, and clofibrate and a similar trend was noted for benzo(a)pyrene and lubricant oil in water exposure experiments (21 days). The catalase activity was reduced or unchanged depending on the mode of exposure of animals. By stereology, significant increases of numerical and volume densities of peroxisomes were found in animals injected for 7 days with lubricant oil or clofibrate. These observations indicate that peroxisomal oxidases in mussels are induced at moderate rates in response to different xenobiotics and that their determination could provide a (sensitive) marker for detection of effects of some toxic pollutants, particularly the lubricant oils which in addition induce significant structural alterations of mussel peroxisomes.

Increased levels of pipecolic acid have been reported in patients with cerebro-hepato-renal syndrome (CHRS) of Zellweger and the general deficiency of peroxisomal function has been implicated in its pathogenesis. We have therefore investigated the capacity of normal peroxisomes to metabolize pipecolic acid. Highly purified peroxisomes were obtained from rat liver and rat and beef kidney cortex by a recently developed method using metrizamide gradients and a vertical rotor. These preparations oxidized D,L-pipecolic acid as evidenced by the measurement of H2O2 production. Incubation with either the D- or L-isomer revealed that almost exclusively D-pipecolate is oxidized. The specific activities proved to be 20-50 times higher in renal than in hepatic peroxisomes. A commercially available crystalline suspension of D-amino acid oxidase from porcine kidney also oxidized the pipecolic acid with the following rates 54:36:1 respectively for D-:,D,L-:L-isomers. Incubation of vibratome sections of rat kidney and liver in a medium containing D-pipecolic acid and cerous ions, revealed electron-dense deposits over the matrix of peroxisomes confirming the localization also by fine structural cytochemistry. These observations demonstrate the capability of mammalian peroxisomes to oxidize pipecolic acid and suggest that the absence or deficiency of peroxisomal D-amino acid oxidase may be implicated in the pathogenesis of hyperpipecolatemia in Zellweger's CHRS.