Résumé
The transcriptional intermediary factor 1 (TIF1) family protein TIF1beta is a corepressor for Krüppel-associated box (KRAB)-domain-containing zinc finger proteins and plays a critical role in early embryogenesis. Here, we examined TIF1beta distribution in the nucleus of mouse embryonic carcinoma F9 cells during retinoic-acid-induced primitive endodermal differentiation. Using confocal immunofluorescence microscopy, we show that, although TIF1beta is diffusely distributed throughout the nucleoplasm of undifferentiated cells, it relocates and concentrates into distinct foci of centromeric heterochromatin in differentiated cells characterized by a low proliferation rate and a well developed cytokeratin network. This relocation was not observed in isoleucine-deprived cells, which are growth arrested, or in compound RXR alpha(-/-)/RAR gamma(-/-) null mutant cells, which are resistant to RA-induced differentiation. Amino-acid substitutions in the PxVxL motif of TIF1beta, which abolish interaction with members of the heterochromatin protein 1 (HP1) family, prevent its centromeric localization in differentiated cells. Collectively, these data provide compelling evidence for a dynamic nuclear compartmentalization of TIF1beta that is regulated during cell differentiation through a mechanism that requires HP1 interaction.