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

The interaction of cells with extracellular matrix components contributes to their specific differentiation. We studied hepatic peroxisomes and their changing features during embryonic development, and we immunolocalized in the same tissue the extracellular matrix components laminin and collagen IV as well as the integrin receptor subunits α₁, α₂, β₁ and β₄. 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 the immunocytochemistry of six peroxisomal proteins. The successive import of catalase and the peroxisomal β-oxidation enzymes, the late appearance of the other enzymes, and the gradual increase of peroxisomal size and number to adult values occurred as asynchronous events. Although still immature, peroxisomes were recognized at every stage examined and coexisted with laminin and collagen IV in both species. The β₁ integrin subunit was immunodetected as early as at 12.5 days in rat. It was concluded that these extracellular matrix factors may be important for the differentiation of liver parenchyma from the liverbud stage onwards. However, the stepwise maturation of the liver-specific peroxisome suggests the involvement of many other regulating factors. ((C) Elsevier, Paris).