Drosophila fushi tarazu. a gene on the border of homeotic function.
BACKGROUND
Hox genes specify cell fate and regional identity during animal development. These genes are present in evolutionarily conserved clusters thought to have arisen by gene duplication and divergence. Most members of the Drosophila Hox complex (HOM-C) have homeotic functions. However, a small number of HOM-C genes, such as the segmentation gene fushi tarazu (ftz), have nonhomeotic functions. If these genes arose from a homeotic ancestor, their functional properties must have changed significantly during the evolution of modern Drosophila.


RESULTS
Here, we have asked how Drosophila ftz evolved from an ancestral homeotic gene to obtain a novel function in segmentation. We expressed Ftz proteins at various developmental stages to assess their potential to regulate segmentation and to generate homeotic transformations. Drosophila Ftz protein has lost the inherent ability to mediate homeosis and functions exclusively in segmentation pathways. In contrast, Ftz from the primitive insect Tribolium (Tc-Ftz) has retained homeotic potential, generating homeotic transformations in larvae and adults and retaining the ability to repress homothorax, a hallmark of homeotic genes. Similarly, Schistocerca Ftz (Sg-Ftz) caused homeotic transformations of antenna toward leg. Primitive Ftz orthologs have moderate segmentation potential, reflected by weak interactions with the segmentation-specific cofactor Ftz-F1. Thus, Ftz orthologs represent evolutionary intermediates that have weak segmentation potential but retain the ability to act as homeotic genes.


CONCLUSIONS
ftz evolved from an ancestral homeotic gene as a result of changes in both regulation of expression and specific alterations in the protein-coding region. Studies of ftz orthologs from primitive insects have provided a "snap-shot" view of the progressive evolution of a Hox protein as it took on segmentation function and lost homeotic potential. We propose that the specialization of Drosophila Ftz for segmentation resulted from loss and gain of specific domains that mediate interactions with distinct cofactors.
Löhr
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U
Department of Biochemistry and Molecular Biology, Mount Sinai School of Medicine, One Gustave L. Levy Place, New York, NY 10029, USA.
Yussa
M
M
Pick
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L
D000595:Amino Acid Sequence; D000818:Animals; D051943:Antennapedia Homeodomain Protein; D002470:Cell Survival; D029721:Drosophila Proteins; D004331:Drosophila melanogaster / Q000254:growth & development; D051717:Fushi Tarazu Transcription Factors; D015870:Gene Expression; D017344:Genes, Insect / Q000502:physiology*; D006110:Grasshoppers; D018398:Homeodomain Proteins / Q000235:genetics / Q000502:physiology*; D008969:Molecular Sequence Data; D009687:Nuclear Proteins; D018336:Receptors, Aryl Hydrocarbon; D014157:Transcription Factors; D014231:Tribolium
D051943:Antennapedia Homeodomain Protein; C497974:Antp protein, Drosophila; D029721:Drosophila Proteins; D051717:Fushi Tarazu Transcription Factors; D018398:Homeodomain Proteins; D009687:Nuclear Proteins; D018336:Receptors, Aryl Hydrocarbon; D014157:Transcription Factors; C497169:ftz protein, Drosophila; C108704:hth protein, Drosophila; C112211:ss protein, Drosophila