SMITH, M.H.; WILLIAMS, N.L.; STELLWAG, E.J.; SCEMAMA, J.L.*: Characterization of a novel Hox group gene 1 from Morone saxatilis

Hox genes are transcription factors that control regional specification of tissues in developing embryos. Our laboratory is working toward the complete characterization of the Hox cluster genes from Morone saxitilis, a member of the order Perciformes. A genomic clone, 11D, was isolated and found to contain a complete paralogous group 1 gene (11D-1). Phylogenetic analysis shows that 11D-1 is most related to Oryzias latipes and Danio rerio Hox-b1b. Whole-mount in situ hybridization of Morone embryos with an 11D-1 exon1-specific antisense riboprobe shows an expression pattern different from the patterns described for Hox-a1a and b1a genes in Danio rerio. These genes in Danio rerio are expressed primarily in the notochord and rhombomeres. 11D-1 is initially expressed in the cell cap during gastrulation, and in the notochord and paraxial mesoderm during neurulation. This early expression fades and by the 14-somite stage, 11D-1 is later expressed dorso-ventrally and in the hindbrain before all expression terminates by 72 hpf (corresponding to the pec fin stage in Danio rerio). The three phase expression, primarily outside of the hindbrain, and the duration of expression are unusual for a paralogous group 1 gene, and suggests that 11D-1 is a gene not previously characterized in teleosts. However, our data indicates that 11D-1 is a member of paralogous group 1 and is most likely a B or D cluster derivative. Additional linkage data will be required to assign 11D-1 to a specific Hox cluster.