5' regulatory region of the bovine keratin 5 (KRT5/BK5) gene that directs expression to basal keratinocytes of stratified squamous epithelia, reproducing the tissue- and cell-type-specific pattern of endogenous keratin 5 in transgenic mice (Ramirez et al. 1994). Used to target transgenes or Cre recombinase to the proliferative basal layer of skin and other stratified epithelia.
Length: 5200 bp
Strength: moderate
Tissue: Basal epithelial cells of stratified squamous epithelia — epidermis, esophageal and foregastric mucosa, cervicovaginal epithelium, and thymic medullary epithelium — recapitulating endogenous keratin 5 expression (Ramirez et al. 1994; Liang et al. 2009)
A genomic fragment spanning roughly -5.3 kb to +138 bp of the bovine keratin 5 gene reproduces the spatial and developmental expression pattern of endogenous K5, restricting reporter expression to stratified epithelia from embryonic day 11.5 onward; a shorter -1.3 kb to +138 bp fragment is inactive, placing the tissue-specific elements between -5.3 and -1.3 kb (Ramirez et al. 1994). A 5.2 kb BK5 fragment drives Cre recombinase in basal epithelial cells of the epidermis, esophageal and foregastric mucosa, cervicovaginal epithelium, and thymic medullary epithelium in transgenic mice, with both tamoxifen-inducible and spontaneous Cre activity depending on the transgenic line (Liang et al. 2009).
Applications: Used to target transgene or Cre recombinase expression to basal keratinocytes and other basal epithelial cell populations across multiple organs — epidermis, esophageal and foregastric mucosa, cervicovaginal epithelium, and thymic medullary epithelium — in transgenic mice, including tamoxifen-inducible BK5-CreERT lines for conditional gene deletion restricted to the basal epithelial compartment (Liang et al. 2009).
Limitations: The minimal -1.3 kb proximal fragment is inactive; the full -5.3 kb region is required for basal-keratinocyte specificity, constraining construct size (Ramirez et al. 1994). Activity is not confined to skin — it is also active in esophageal, foregastric, cervicovaginal, and thymic medullary basal epithelium, so it is not a skin-exclusive driver (Liang et al. 2009).
Liang et al. (2009).
Transgenic mice exhibiting inducible and spontaneous Cre activities driven by a bovine keratin 5 promoter that can be used for the conditional analysis of basal epithelial cells in multiple organs.
J Biomed Sci - Liang 2009 BK5 CreERT
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