Nuclear import of cellular retinoic acid-binding protein type I in mouse embryonic cells.

Using confocal microscopy we show that cellular retinoic acid-binding protein type I (CRABP I), expressed in several embryonic cell types, displays a compartmentalized subcellular distribution. The protein was excluded from the nucleus in some cells, while in others it accumulated in the nucleus. In the rat cerebellar cell line ST15A, which expresses CRABP I, the protein was found in the cytoplasm with a prominent nuclear exclusion. Addition of retinoic acid to embryos in vivo and to ST15 A cells in vitro did not affect the localization of the protein. Localization of CRABP I and CRABP I fused to a nuclear localization signal expressed in transfected cells, suggested that cell-specific factors may regulate nuclear import of CRABP I. The potential role of a CRABP I-controlled nuclear import of retinoic acid is discussed.