Abstract
Canonical Wnt signaling plays multiple roles in lung organogenesis and repair by regulating early progenitor cell fates: investigation has been enhanced by canonical Wnt reporter mice, TOPGAL, BATGAL and Axin2LacZ. Although widely used, it remains unclear whether these reporters convey the same information about canonical Wnt signaling. We therefore compared beta-galactosidase expression patterns in canonical Wnt signaling of these reporter mice in whole embryo versus isolated prenatal lungs. To determine if expression varied further during repair, we analyzed comparative pulmonary expression of beta-galactosidase after naphthalene injury. Our data show important differences between reporter mice. While TOPGAL and BATGAL lines demonstrate Wnt signaling well in early lung epithelium, BATGAL expression is markedly reduced in late embryonic and adult lungs. By contrast, Axin2LacZ expression is sustained in embryonic lung mesenchyme as well as epithelium. Three days into repair after naphthalene, BATGAL expression is induced in bronchial epithelium as well as TOPGAL expression (already strongly expressed without injury). Axin2LacZ expression is increased in bronchial epithelium of injured lungs. Interestingly, both TOPGAL and Axin2LacZ are up regulated in parabronchial smooth muscle cells during repair. Therefore the optimal choice of Wnt reporter line depends on whether up- or down-regulation of canonical Wnt signal reporting in either lung epithelium or mesenchyme is being compared.
Highlights
Canonical Wnt signaling plays multiple roles during lung organogenesis and repair by controlling survival, proliferation and differentiation of early progenitor cells in epithelium and mesenchyme [1,2]
Further specific expression is seen in the apical ectodermal ridge (AER) of the limb, and epithelium of the mammary placode (Fig. 1A)
We exploited the stable Axin2LacZ line to provide an internal control for the older TOPGAL and BATGAL lines where random insertion may alter expression from the original reports
Summary
Canonical Wnt signaling plays multiple roles during lung organogenesis and repair by controlling survival, proliferation and differentiation of early progenitor cells in epithelium and mesenchyme [1,2]. Canonical Wnt signaling is mediated mainly by the multifunctional beta-catenin protein which is a potent coactivator of transcription factors such as Lymphoid Enhancer Factor (LEF) and T Cell Factor (TCF) [3]. The Tcf optimal promoter (TOP)-beta-galactosidase (TOPGAL) transgenic mice were made fusing three LEF/TCF binding sites to c-fos minimal promoter [9]. These mice were originally reported to follow activation of LEF/ TCF transcription complexes during hair development and differentiation. The second reporter line, the s-catenin activated transgene (BAT) driving the expression of nuclear beta-galactosidase, was designed by fusing seven TCF/LEF binding sites upstream of a 0.13 kb fragment containing the minimal promoterTATA box of the Siamois gene [10]. Transgenic mice relying upon random insertion of an expression cassette may be unstable with increased number of generations
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