Figure 1. Efficient and specific inducible lineage labeling of the biliary compartment in R26^Tom Hnf1b-CreER animals.

(A) In the adult mouse, HNF1β was specifically expressed in bile ducts and biliary ductules/canals of Hering (arrows). HNF1β⁺ cells were identical with SOX9⁺ and CK19⁺ cells, as assessed by co-IF (HNF1β⁺/SOX9⁺: 97.04% ± 0.52%, n = 3; HNF1β⁺/CK19⁺: 99.89% ± 0.10%, n = 5), while HNF1β expression in HNF4α⁺ hepatocytes was virtually absent (0.008% ± 0.004%, n = 8). (B) Cre-induced expression of the fluorescent dye tdTom was determined in 5- to 6-week-old R26^Tom Hnf1b-CreER reporter mice 7 days after a single tamoxifen injection. tdTom expression was restricted to HNF1β⁺/SOX9⁺/CK19⁺ bile ducts and periportal ductules (n = 5), whereas labeling of HNF4α⁺ hepatocytes was a rare event (0.012% ± 0.003%, n = 10). All periportal areas revealed a high tdTom labeling efficacy of the HNF1β⁺ compartment (>30 portal tracts per mouse were quantified at ×600 magnification from 3 discontinuous sections; mean labeling efficiency: 84.3% ± 0.6%; n = 5 animals). BD, bile duct; PV, portal vein; Tam, tamoxifen. Scale bar: 20 μm.