Nomenclature of Hox genes

By | May 6, 2021
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Lots of confusion prevailed in nomenclature Hox genes , even the name Hox was confusing. A hox gene originally referred to any gene coding for a protein with Homeodomain. In the beginning very few genes where known which could be clearly identified with homeotic mutants of Drosophila. Later huge number of genes with Homeodomain were identified which does not show homeotic property(transforming one segment to another when mutated). So the name HOX became ambiguous. But now the general consensus is that the term Hox is used only for Homeotic genes and genes which code for proteins with similar homeodomain but lack Homeotic property are given different names.e.g. Para Hox and NK genes.

Drosophila has eight Hox genes in two clusters Antennapedia complex and Bithorax complex.

Antennapedia complex has following genes:

1. Labial (symbol : lab) vertebrate Homolog is HOX A1,HOXB1,HOX C1.
2. Proboscipedia (pb) Vertebrate Homolog is HOX A2,HOXB2.
Two other Homeodomain genes are present betweem Pb and Dfd are present . They are zerknüllt, Bicoid (zen, bcd) and their Vertebrate Homologs are HOX A3,HOX B3,HOXD3. But note that both homologs of Hox 3 in Drosophila (zen , bcd ) are not homeotic genes.
3. Deformed (Dfd) Vertebrate Homolog HOX A4, HOX B4, HOXC4, HOXD4.
4. Sex combs reduced (Scr) Vertebrate Homolog HOX A5, HOXB5, HOXC5.

Between Scr and Antp , there is one more non hox gene called fuzhi tarazu (ftz) is present. ftz has segmentaion function in Drosophila while in Tribolium it retains some Hox function.

5. Antennapedia (Antp) Vertebrate Homolog HOX A6, HOXB6, HOXC6.

Bithorax Complex:

6. Ultrabithorax (Ubx) Vertebrate Homolog Hox A7, HOXB7, HOXC7, HOXD7.
7. Abdominal A (abdA) Vertebrate Homolog HOX B8
8. Abdominal B (AbdB) Vertebrate Homolog HOX A,B,C,D 9-13.

Fly Hox gene symbols:
When a Hox gene was discovered in fruit fly ,it was given a name by discoverer based on the phenotype. If the first mutant isolated was dominant then the symbol of the gene begins with capital letter e.g. Dfd, Scr , Antp, Ubx, AbdB and if the first mutant isolated was recessive the small letter e.g.lab, pb and  adbA.