Secretion of collagen by insects: Autoradiographic study of l-proline 3H-5 incorporation by the firebrat Thermobia domestica

The biosynthesis of collagenous endoskeletal endosterna by fibroblasts was studied by electron microscope autoradiography after tritium-labelled proline administration in the firebrat Thermobia domestica at various time intervals. Autoradiographs were quantitatively analyzed and the relative concentration of label was determined for various cellular compartments. The labelling in the rough endoplasmic reticulum, ground cytoplasm, Golgi apparatus and endosterna was compared during the secretion of radioactive products. The label, initially located in the rough endoplasmic reticulum was found in the Golgi apparatus before it accumulated in the endosternum. The involvement of the rough endoplasmic reticulum and Golgi apparatus in the transport of secreted collagen is discussed, comparing our results with current knowledge of collagenous secretion.