In this review we would like to summarize our current knowledge on the biogenesis of mammalian peroxisomes and discuss in detail single steps which led to the current model of peroxisome biogenesis. Since some recent results obviously are not fully compatible with this model a revised version is discussed.
In 1964 Novikoff and Shin' described the existence of continuities between peroxisomes and the endoplasmic reticulum (ER) in normal rat liver indicating that the ER plays an important role in the biogenesis of peroxisomes. During the following years ER-peroxisome continuities were also reported to occur in other tissues2 and the idea settled that peroxisomes are derived by budding from the ER. We will not review this aspect of continuities between the membranes of the ER and peroxisomes since this has been done extensively before by Bock et aL3 and Lazarow et aL4 drawing the conclusion that such continuities have not been demonstrated convincingly. In accordance with this, by serial section analysis and three-dimensional reconstruction of the peroxisomal compartment of mouse sebaceous gland and liver, Gorgas'.' demonstrated that peroxisomes are rather complex structures characterized by tortuous, elongated and branched tubular segments of varying diameter. Thus, interconnections previously believed to exist between peroxisomes and the ER were demonstrated to be part of a polymorphous peroxisomal compartment recently also observed in regenerating rat liver.7 Together with other ultrastructural investigations that were unable to demonstrate ER-peroxisome continuities8v9 recent