Maturation of the liver-specific peroxisome versus laminin, collagen IV and integrin expression

The interaction of cells with extracellular matrix components contributes t o their specific differentiation. We studied hepatic peroxisomes and their changing features during embryonic development, and we immunolocalized in t he same tissue the extracellular matrix components laminin and collagen IV as well as the integrin receptor subunits alpha(1), alpha(2), beta(1) and b eta(4). Rat and human embryonic liver peroxisome expression were studied at the light- and electron-microscopic level by means of localizing catalase- , D-amino acid oxidase- and polyamine oxidase activities and by means of th e immunocytochemistry of six peroxisomal proteins. The successive import of catalase and the peroxisomal beta-oxidation enzymes, the late appearance o f the other enzymes, and the gradual increase of peroxisomal size and numbe r to adult values occurred as asynchronous events. Although still immature, peroxisomes were recognized at every stage examined and coexisted with lam inin and collagen TV in both species. The PI integrin subunit was immunodet ected as early as at 12.5 days in rat. It was concluded that these extracel lular matrix factors may be important for the differentiation of liver pare nchyma from the liverbud stage onwards. However, the stepwise maturation of the liver-specific peroxisome suggests the involvement of many other regul ating factors. ((C) Elsevier, Paris).