The cDNA sequence of Stra7, a retinoic acid (RA)-inducible gene in P19 embryonal carcinoma (EC) cells, was determined. The deduced Stra7 protein contains a homeodomain highly similar to that of the previously described chicken CHox7 gene product, and is highly conserved during evolution, from hemichordates to vertebrates. The mouse Stra7 cDNA corresponds to the full-length form of the 77 bp homeodomain-encoding cDNA fragment which was previously cloned and termed MMoxA or Gbx-2. Reverse-transcriptase-PCR analysis revealed the presence of Stra7/Gbx-2 transcripts in the adult brain, spleen, and female genital tract, whereas no expression could be observed in heart, liver, lung, kidney, or testes. In situ hybridization analysis showed a restricted expression pattern of Stra7/Gbx-2 in the three primitive germ layers during gastrulation. Restricted expression was also detected in the pharyngeal arches. Subsequently, there were specific expression domains in the developing central nervous system, at the midbrain/hindbrain boundary and later in the cerebellum anlage, in certain rhombomeres, in dorsal regions of the spinal cord, and in the developing dorsal thalamus and corpus striatum.