GENOMIC SEQUENCE AND EMBRYONIC EXPRESSION OF THE ZEBRAFISH HOMEOBOX GENE HOX-3.4

We have analyzed the genomic DNA sequence and embryonic expression pat tern of the zebrafish hox-3.4 gene. Two exons, encoding a protein with a total size of 232 amino acids, were identified within a 3.5 kbp gen omic region. Besides the homeodomain, which is identical to that of th e human HOX3D and mouse Hox-3.4 genes, the first 58 residues of the N- terminal domain in the predicted Hox-3.4 protein share 48% sequence id entity with the gene product of the human cognate. Some of the N-termi nal sequence elements are also conserved relative to the two other mem bers of the Hox-1.3/Hox-2.1/Hox-3.4 paralogy group. In addition, the p aralogous genes share a significant degree of sequence identity in non -coding regions. This conservation is particularly evident in the prom oter regions of the cognates hox-3.4, Hox-3.4, and HOX3D, where a 180 bp TATA-box-containing element with a 60% identity is located. This is in agreement with the previous finding that the HOX3D promoter region contains response elements for other Hox proteins and retinoids. Also with respect to embryonic expression, the zebrafish hox-3.4 gene is v ery similar to its mammalian counterparts. Within the central nervous system of 16, 24, and 48 h embryos, hox-3.4 transcripts were detected throughout most of the spinal cord from a boundary at the posterior en d of the hindbrain. In 16 h embryos the hox-3.4 gene is also active wi thin a restricted region of the tailbud.