Abstract
We investigated the characteristics of extracellular matrix (ECM) in the soft tissue of two frozen baby woolly mammoths (Mammuthus primigenius) that died and were buried in Siberian permafrost approximately 40,000 years ago. Morphological and biochemical analyses of mammoth lung and liver demonstrated that those soft tissues were preserved at the gross anatomical and histological levels. The ultrastructure of ECM components, namely a fibrillar structure with a collagen-characteristic pattern of cross-striation, was clearly visible with transmission and scanning electron microscopy. Type I and type IV collagens were detected by immunohistochemical observation. Quantitative amino acid analysis of liver and lung tissues of the baby mammoths indicated that collagenous protein is selectively preserved in these tissues as a main protein. Type I and type III collagens were detected as major components by means of liquid chromatography-mass spectrometry analysis after digestion with trypsin. These results indicate that the triple helical collagen molecule, which is resistant to proteinase digestion, has been preserved in the soft tissues of these frozen mammoths for 40,000 years.
Highlights
Collagen is an extracellular matrix protein and occurs in all types of animal tissue
Positive reactions to anti-type IV (Fig 5A) and type I (Fig 5B) collagen antibodies were observed in extracellular matrix (ECM) components of the lung specimen from Masha by immunofluorescence
These results indicate that ECM components, including collagens, were stable and have been preserved in the tissues of these frozen mammoths for 40,000 years
Summary
Collagen is an extracellular matrix protein and occurs in all types of animal tissue. Collagen is greatly affected by post-translational modifications, such as hydroxylation of proline and lysine, cross-link formation, and glycosylation of lysine, that are not directly defined by DNA information [2]. For this reason, collagen analysis can yield unique information about extinct animals. Several studies have detected collagen in hard tissue (e.g. bone and dentine) from mammoths (Mammuthus columbi) [3,4,5], but there have been no reports on protein analysis of mammoth soft tissue.
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