Ultrabithorax

Ultrabithorax or Ubx is a member of the homeobox gene family. In "Drosophila melanogaster" it is expressed in the T3 and A1 segments and represses wing formation. The Ubx gene regulates the decisions regarding the number of wings and legs the adult Drosophila melanogaster will have. Ubx is activated when there is a certain amount of Hunchback protein, which is a product of a gap gene. The concentrations of Hunchback only exist in the middle region of the embryo, therefore Ubx is expressed only in these segments as well.

Ubx is coded for by a 5' exon, two micro-exons, an optional B element, and a C terminal exon. The Ubx genomic DNA length is 76 kb and it's cDNA clone length is 3.2 to 4.6 kb. The 5' exon contains the 5'UTR which has 964 bases. The C terminal exon contains the 3'UTR which has 1580 to 2212 bases.

Ubx represses selected Dpp target genes in the anterior and posterior axis. Ubx represses Wingless in the posterior compartment of the dorsoventral axis. Ubx also selectively represses one enhancer of the vestigial genes in the proximodistal axis.

Mutations of the Ubx gene will lead to transformation of dorsal and ventral appendages of the third thoracic segment(T3), which includes the haltere and third leg, into the counterparts on the second thoracic segment(T2). If Ubx is present in T3, it will prevent the original fate of the T2 segment. Such mutations can produce a second set of wings.

The developmental role of Ubx is determine by the splicing that takes place during development. Certain splice factors of a particular cell allow that cell to regulate the developmental fate of that cell by making different splice variants of transcription factors.

Alternate splicing of the Ubx transcript produces a family of five proteins, called Ubx isoforms. These proteins function as transcription factors.