The structural and functional polarity of the hepatic human/rat hybrid WIF-B is a stable and dominant trait

WIF-B cells were generated previously to obtain a good in vitro model expre ssing the structural and functional polarity of hepatocytes, Here we tested the stability and the strength of the WIF-B polarized phenotype. WIF-B cel ls stayed polarized and formed functional bile canaliculi even after 3 mont hs in culture or after injection in nude mice and culture of the resulting tumors. WIF-B was subcloned and 10,000 colonies were examined; all (except for 3) were composed of bile canaliculi forming cells, Some subclones were characterized; the polarized ones presented the same properties and karyoty pe as the WIF-B cells; the 3 unpolarized subclones had a lower level of E-c adherin and different karyotypes, WIF-B cells were fused with their nonpola rized hepatic parental cells. The polarity state of the resulting FWIF hybr ids was studied from day 11 to day 38 after fusion, by immunolocalization o f hepatocyte domain-specific plasma membrane proteins. Most FWIF colonies ( >80%) were composed of polarized cells. Soon after fusion these cells were exclusively polarized as simple epithelial cells. The percent of colonies c ontaining cells expressing the typical hepatocyte polarity increased with t ime and reached 80% at day 38. This result confirms the two-step polarizati on process previously described for WIF-B, Chromosomally complete FWIF hybr ids were examined several months after fusion, As shown by the study of bil e acid transport and by confocal analysis of the localization of membrane d omain markers, FWIF cells expressed a functional and fully polarized hepati c phenotype, In conclusion, polarity is a stable and dominant trait of WIF- B.