3.6 kb 5' flanking fragment of the rat Col1a1 gene (ColCAT3.6), first shown by Bogdanovic et al. (1994) to drive expression in bone, tooth, and tendon of transgenic mice. Used to mark and manipulate osteoblasts and other collagen type I-producing mesenchymal cells across their differentiation.
Length: 3632 bp
Strength: moderate
Tissue: Osteoblasts and osteoblast-lineage cells, odontoblasts, and tendon fibroblasts; not active in non-collagen-producing tissues (Bogdanovic et al., 1994)
Expression: constitutive
Origin: Rattus norvegicus Col1a1 gene, -3521 to +115 5' flanking fragment
Characteristics
3.6 kb fragment (-3521 to +115 relative to the transcription start site) of the rat Col1a1 gene, designated ColCAT3.6 by Bogdanovic et al. (1994), who showed it is active in bone and tendon of transgenic mice, unlike the shorter 1.7 kb deletion which is inactive; sequences controlling tendon expression lie between -3.5 and -1.7 kb. Dacic et al. (2001) showed the 3.6 kb fragment initiates transgene expression earlier in osteoblast differentiation (coincident with alkaline phosphatase and type I collagen mRNA onset) than the shorter 2.3 kb fragment, which activates later, at the bone sialoprotein/mineralization stage.
Applications: Marking and manipulating osteoblasts and osteoblast-lineage precursors, tenocytes/tendon fibroblasts, and other collagen type I-producing mesenchymal cells in transgenic mice, including reporter (CAT, GFP) and Cre-driver lines for bone and connective-tissue research.
Limitations: Requires sequences out to -3.5 kb for tendon expression and to -2.3/-1.7 kb for bone/tooth expression (Bogdanovic et al., 1994); shorter deletions lose tissue coverage. As a fragment of the endogenous gene rather than a synthetic strong promoter, expression level and onset timing vary with differentiation stage and, in transgenic lines, with integration site.
