The TGIF homeobox gene encodes a homeoprotein that represses the 9-cis retinoic acid receptor-dependent transcription activation. To investigate the potential role of this gene in vertebrate development, we have isolated cDNA clones of the murine TGIF (mTGIF) gene and analyzed its expression pattern during mouse embryogenesis and postnatal development by Northern analysis, reverse transcriptase-polymerase chain reaction (RT-PCR), and in situ hybridization histochemistry. mTGIF transcripts were detected at day E16 in the emerging external granular layer (EGL), the cells of which arise from the proliferating cerebellar neuroepithelium. Expression of mTGIF transcripts was also detected at day E16 in the proliferating cells in the neuroepithelium of the hippocampal formation. Following gestation, mTGIF expression increases to a maximum between postnatal days 5 and 10 (PN5 and PN10) in the rapidly expanding cerebellar EGL. mTGIF transcripts are no longer detectable when EGL proliferation ceases on approximately day PN15. Throughout embryo development and in the adult mice, TGIF is detected in a restricted number of tissues, mostly in proliferating and differentiating cell lineages, such as tongue and testis. Our results suggest that the TGIF gene regulates target genes involved in the proliferation, migration, and/or differentiation of particular neuronal cell lineages in the developing brain.