THE EXPRESSION PATTERN OF THE MURINE HOXA-10 GENE AND THE SEQUENCE RECOGNITION OF ITS HOMEODOMAIN REVEAL SPECIFIC PROPERTIES OF ABDOMINAL B-LIKE GENES

Homeobox genes of the Abdominal B (AbdB) family constitute a distinct subset of vertebrate Hox genes. Analysis of the murine Hoxa-10 gene, o ne member of this family, revealed several properties specific to this class. Two transcripts of Hoxa-10, a10-1 and a10-2, encode homeodomai n proteins of 55 kDa (399 amino acids) and 16 kDa (96 amino acids), re spectively, These proteins have identical homeodomains and C-terminal regions encoded by a common 3' exon but differ significantly in the si zes of their N-terminal regions because of the usage of alternative 5' exons, The 5' exon of the a10-2 form is also present in transcripts o f Hoxa-9, the next 3' gene, indicating that splicing can occur between adjacent AbdB Hox genes within a cluster, Both Hoxa-10 transcripts de monstrated identical patterns of expression in the posterior body and proximal limb bud, differentiating them from AbdB morphogenetic and re gulatory transcripts and suggesting a role,vith other AbdB Hox genes i n the patterning of these structures, Finally, a binding site selectio n identified the sequence AA(A/T)TTTATTAC as the Hoxa-10 homeodomain c onsensus binding site, with a TTAT core sequence. Preferential recogni tion of a TTAT core therefore differentiates the AbdB class from Anten napedia (Ante) class gene products which bind a TAAT core. Thus, in ve rtebrates, structural similarities, coordinate transcriptional regulat ion, sites of expression, and binding site preferences all serve to di stinguish AbdB from Antp Hox genes.