HB9: Proteins and Enzymes

The homeobox gene Hb9/Hlxb9, is expressed selectively by motor neurons (MNs) in the developing vertebrate CNS. Hb9, which encodes a factor central to MN development regulates neuronal fate by restricting expression of Lim3 and Even-skipped (Eve), two homeodomain (HD) proteins required for development of distinct neuronal classes. In the vertebrate CNS, HB9/MNR2 transcription factors are specifically expressed in all somatic motoneurons and are necessary to distinguish motoneurons from interneurons. Hb9 is also a transcription factor expressed in lymphoid and pancreatic tissue. In humans, HB9 mutation causes an autosomal dominant form of sacral agenesis.