Type XVIII collagen : characterization of the primary structure and expression pattern of different variants in <em>Xenopus laevis</em>, characterization of the human gene structure and analysis of transgenic mice expressing endostatin
Elamaa, Harri (2004-11-23)
In this work the type XVIII collagen has been studied by using several approaches, such as different animal models. The primary structure of frog, Xenopus laevis, type XVIII collagen and the expression pattern of its variants during early embryogenesis have been elucidated. The gene structure of human type XVIII collagen was characterized and the localization and processing of its longest variant was studied by generated antibodies. In addition, the function of the proteolytically released C-terminal part of type XVIII collagen, endostatin, was studied by generating transgenic mice expressing endostatin.
The primary structure of X. laevis type XVIII collagen is comprised of three N-terminal variants resembling their mammalian counterparts. The sizes of the polypeptides are 1285, 1581, and 1886 residues. The most conserved regions are the C-terminal endostatin region and the cysteine-rich domain in the N-terminus. Whole-mount in situ hybridization reveals different expression patterns for variants during embryogenesis. The short variant is the most abundant, whereas the two longest variants exhibit more restricted expression.
The gene structure of human type XVIII collagen reveals an exon-intron organization that is conserved with mouse. The length of the human gene is about 105 kb and contains 43 exons. The third variant of type XVIII collagen has a conserved cysteine-rich domain with homology to the extracellular part of frizzled proteins. This third variant is localized to developing muscle and lung, and is also found in serum. In cell culture, the proteolytic fragments of the N-terminus, including the cysteine-rich motif, are also detected.
Endostatin function was studied by generating mouse lines expressing endostatin under the keratin-14 promoter, which drives the expression mainly in the skin. Three independent transgenic mouse lines were achieved with varied expression levels. The phenotype was seen in the eye with lens opacity and abnormal morphology of epithelial cells in the lens. In the skin, a broading of the basement membrane in the epidermis dermis junction was detected. Immunoelectron microscopy analysis revealed a polarized orientation of type XVIII collagen in the basement membrane. In transgenic mice, altered localization of endogenous type XVIII collagen was seen, suggesting displacement of the endogenous type XVIII collagen with transgenic endostatin leading to disorganized basement membrane.
- Avoin saatavuus