HOM-C evolution in Drosophila: is there a need for Hox gene clustering?

The conservation of Homeotic (Hox) gene clustering and colinearity in many metazoans indicates that functional constraints operate on this genome organization. However, several studies have questioned its relevance in Drosophila. Here, we analyse the genomic organization of Hox and Hox-derived genes in 13 fruitfly species and the mosquito Anopheles gambiae. We found that at least seven different Homeotic complex (HOM-C) arrangements exist among Drosophila species, produced by three major splits, five microinversions and six gene transpositions. This dynamism contrasts with the stable organization of the complex in many other taxa. Although there is no evidence of an absolute requirement for Hox gene clustering in Drosophila, we found that strong functional constraints act on the individual genes. The conservation of Homeotic (Hox) gene clustering and colinearity in many metazoans indicates that functional constraints operate on this genome organization. However, several studies have questioned its relevance in Drosophila. Here, we analyse the genomic organization of Hox and Hox-derived genes in 13 fruitfly species and the mosquito Anopheles gambiae. We found that at least seven different Homeotic complex (HOM-C) arrangements exist among Drosophila species, produced by three major splits, five microinversions and six gene transpositions. This dynamism contrasts with the stable organization of the complex in many other taxa. Although there is no evidence of an absolute requirement for Hox gene clustering in Drosophila, we found that strong functional constraints act on the individual genes. describes the observation that Hox genes are arranged in the chromosome in the same order as they are expressed along the anteroposterior body axis of metazoans (spatial colinearity) and/or in the same order as their temporal expression in development (temporal colinearity). movement of a relatively small genomic segment, containing usually one or a few genes, from one chromosomal position to another. Genes can transpose by several mechanisms including retroposition (which implies reverse transcription of RNA and insertion of the resultant cDNA into a different genome site) and transposon-mediated excision and insertion of genomic segments. cluster of Hox genes located (usually) in a single chromosomal site. genes that determine the identity of individual segments or body regions in early embryos of metazoans. those that cause body regions to develop structures appropriate to other regions. Hox genes that have lost their homeotic function or are derived (by duplication) from such a gene. a small inversion containing at most a few genes that cannot be cytologically detected. a chromosomal inversion that does not include the centromere. This seems to be the most common type of chromosomal alteration in the evolution of the genus Drosophila. refers to the transmission of unchanged traits from ancestor to descendant species (i.e. the fact that a trait can persist in a lineage for a long time after the cessation of the selective forces that have produced or maintained it).