Nomenclature of Hox genes
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 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.
Zerknüllt, Bicoid (zen,bcd) Vertebrate Homolog 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.
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 adbA.
Representatives of the same paralog group are colored identically.
Vertebrate Hox nomenclature:
Intiaally there was all sought of naming in vertebrate Hox world but after the meeting entitled “The Homeobox in Development” in Ascona, Switzerland, organized by Professor W.Gehring new system of nomenclature was introduced for vertebrate Hox genes.
There are four clusters of Hox genes in vertebrates which have arised byt wo duplication events,known
as A, B, C, and D. Based on sequence similarity the genes can be sorted into 13 ‘paralog’ groups. The order of paralogs along the chromosome is preserved in the four complexes. The genes within a complex are transcribed in the same direction and are numbered according to their paralog group from 1 at the 3′ end to 13 at the 5′ end. In several cases a member of a paralog group is absent from a complex, in which case the corresponding gene number is omitted.
Reference:
MP Scott
Vertebrate Homeobox Gene Nomenclature
Cell, Vol. 71, 551-553, November 13, 1992,
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