The homeobox is a 180-bp DNA sequence that encodes a DNA-binding domain known as a homeodomain. See 142950. To identify additional homeobox genes, Matsui et al. (1993) performed PCR using genomic DNA and degenerate primers based on conserved regions of the homeodomain. They isolated fragments of 2 novel homeobox genes, GBX1 (603354) and GBX2. The predicted amino acid sequences of the GBX1 and GBX2 homeodomains were identical. Matsui et al. (1993) reported that the GBX2 gene is the human homolog of the mouse MMoxA, or Gbx2, gene identified by Murtha et al. (1991).

Lin et al. (1996) used PCR to amplify portions of homeobox genes present in a human 11-week fetal brain cDNA library. One of these PCR products was determined by sequencing to be the GBX2 gene, so-called for 'gastrulation and brain specific-2.' Screening the human fetal brain cDNA library probes specific for GBX2 led to the identification of a 2151-bp cDNA clone. The nucleotide sequence of the cDNA clone encodes a protein of 347 amino acid residues. The amino acid sequence of the GBX2 homeodomain was found to be identical (100%) to that of the homologous gene, Gbx2, expressed in the developing mouse embryo and virtually identical (97%) to a gene expressed in the developing chick embryo, CHox7.

Chapman et al. (1997) found that the mouse Gbx2 gene contains a single intron, a feature of the human GBX2 gene.

Chapman et al. (1997) extended the known expression pattern of Gbx2 beyond the gastrulation-stage embryo and the developing CNS to pluripotent cells in vitro and in vivo. Gbx2 expression was demonstrated in undifferentiated embryonic stem cells but was downregulated in differentiated cell populations. In the embryo, Gbx2 expression was detected before primitive streak formation, in the inner cell mass of the preimplantation embryo. Chapman et al. (1997) suggested Gbx2 as a candidate control gene for cell pluripotency and differentiation in the embryo.

By fluorescence in situ hybridization, Matsui et al. (1993) mapped the GBX2 gene to 2q37. Lin et al. (1996) confirmed that localization using fluorescence in situ hybridization and analysis of somatic cell hybrids. Lin et al. (1996) observed that the GBX2 and DLX1 (600029)/DLX2 (126255) genes, both expressed in the basal telencephalon, are located in rather close proximity on 2q.

Chapman et al. (1997) mapped Gbx2 to mouse chromosome 1.

The mid/hindbrain junction can act as an organizer to direct the development of the midbrain and anterior hindbrain. In mice, Otx2 (600037) is expressed in the forebrain and midbrain and Gbx2 is expressed in the anterior hindbrain, with a shared border at the level of the mid/hindbrain organizer. Millet et al. (1999) demonstrated that in Gbx2 -/- mutants, the earliest phenotype is a posterior expansion of the Otx2 domain during early somite stages. Furthermore, organizer genes are expressed at the shifted Otx2 border, but not in a normal spatial relationship. To test whether Gbx2 is sufficient to position the mid/hindbrain organizer, Millet et al. (1999) transiently expressed Gbx2 in the caudal Otx2 domain and found that the Otx2 caudal border was indeed shifted rostrally, and a normal-appearing organizer formed at this new Otx2 border. Transgenic embryos then showed an expanded hindbrain and a reduced midbrain at embryonic day 9.5 to 10. Millet et al. (1999) proposed that the formation of a normal mid/hindbrain organizer depends on a sharp Otx2 caudal border and that Gbx2 is required to position and sharpen this border.

By ectopically expressing Otx2 in the murine presumptive anterior hindbrain using a knockin strategy into the En1 (131290) locus, Broccoli et al. (1999) investigated whether the caudal limit of Otx2 expression is instrumental in positioning the isthmic organizer (midbrain/hindbrain junction) and in specifying midbrain versus hindbrain fate. Transgenic offspring displayed a cerebellar ataxia. Morphologic and histologic studies of adult transgenic brains revealed that most of the anterior cerebellar vermis is missing, whereas the inferior colliculus is complementarily enlarged. During early neuronal pattern formation, expression of the midbrain markers Wnt1 (164820) and ephrin A5 (601535), the isthmic organizer markers Pax2 (167409) and Fgf8 (600483), and the hindbrain marker Gbx2 are shifted caudally in the presumptive hindbrain territory. Broccoli et al. (1999) concluded that the caudal limit of Otx2 expression is sufficient for positioning the isthmic organizer and encoding caudal midbrain fate within the mid/hindbrain domain.