Developmental expression of a type II collagen/β‐galactosidase fusion gene in transgenic mice

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Abstract
The correct temporal and spatial expression of the type II collagen gene is believed to be important for normal development and growth of the skeleton and the eye, i.e., tissues where the protein product is predominantly found. To study transcriptinal activation of type II collagen gene in skeletal and nonskeletal tissues we produced transgenic mice carrying murine proα1(II) collagen/β‐galactosidase fusion gene constructs. The expression of the fusion gene was found to depend on the presence of intron 1 sequences: constructs with most of intron 1 deleted failed to reveal any β‐galactosidase activity confirming the important role of regulatory sequences within intron 1 of the gene. High‐level expression of the functional construct was clearly confined to cartilaginous tissues but transient low‐level expression was also observed in extraskeletal locations, such as the developing brain and the notochord. The results demonstrate that the regulatory elements in the proα1(II) collagen/β‐galactosidase fusion gene construct confer both temporal and spatial specificity indistinguishable from that of the endogenous proα1(II) collagen gene as determined by the presence of the corresponding mRNA by in situ hybridization. Furthermore the β‐galactosidase activity correlated well with the progression of chondrogenesis as seen by staining of whole mouse embryos with Alizarin red S and Alcian blue in the hybrid mouse strain used for microinjections. The transgenic mouse line produced should prove useful for studies on various aspects of chondrogenesis. Furthermore, the data shows that the regulatory elements present in the construct are sufficient for targetting the expression of other genes in cartilage.