@article {45740,
	title = {The function and regulation of Ultrabithorax in the legs of Drosophila melanogaster.},
	journal = {Dev Biol},
	volume = {308},
	year = {2007},
	month = {2007 Aug 15},
	pages = {621-31},
	abstract = {<p>Alterations in Hox gene expression patterns have been implicated in both large and small-scale morphological evolution. An improved understanding of these changes requires a detailed understanding of Hox gene cis-regulatory function and evolution. cis-regulatory evolution of the Hox gene Ultrabithorax (Ubx) has been shown to contribute to evolution of trichome patterns on the posterior second femur (T2p) of Drosophila species. As a step toward determining how this function of Ubx has evolved, we performed a series of experiments to clarify the role of Ubx in patterning femurs and to identify the cis-regulatory regions of Ubx that drive expression in T2p. We first performed clonal analysis to further define Ubx function in patterning bristle and trichome patterns in the legs. We found that low levels of Ubx expression are sufficient to repress an eighth bristle row on the posterior second and third femurs, whereas higher levels of expression are required to promote the development and migration of other bristles on the third femur and to repress trichomes. We then tested the hypothesis that the evolutionary difference in T2p trichome patterns due to Ubx was caused by a change in the global cis-regulation of Ubx expression. We found no evidence to support this view, suggesting that the evolved difference in Ubx function reflects evolution of a leg-specific enhancer. We then searched for the regulatory regions of the Ubx locus that drive expression in the second and third femur by assaying all existing regulatory mutations of the Ubx locus and new deficiencies in the large intron of Ubx that we generated by P-element-induced male recombination. We found that two enhancer regions previously known to regulate Ubx expression in the legs, abx and pbx, are required for Ubx expression in the third femur, but that they do not contribute to pupal expression of Ubx in the second femur. This analysis allowed us to rule out at least 100 kb of DNA in and around the Ubx locus as containing a T2p-specific enhancer. We then surveyed an additional approximately 30 kb using enhancer constructs. None of these enhancer constructs produced an expression pattern similar to Ubx expression in T2p. Thus, after surveying over 95\% of the Ubx locus, we have not been able to localize a T2p-specific enhancer. While the enhancer could reside within the small regions we have not surveyed, it is also possible that the enhancer is structurally complex and/or acts only within its native genomic context.</p>
},
	keywords = {Animals, Base Sequence, Body Patterning, DNA, Drosophila, Drosophila melanogaster, Drosophila Proteins, Enhancer Elements, Genetic, Evolution, Molecular, Extremities, Female, Gene Expression Regulation, Developmental, Genes, Homeobox, Genes, Insect, Genetic Complementation Test, Homeodomain Proteins, Male, Mutation, Recombination, Genetic, Species Specificity, Transcription Factors},
	issn = {0012-1606},
	doi = {10.1016/j.ydbio.2007.06.002},
	author = {Davis, Gregory K and Srinivasan, Dayalan G and Wittkopp, Patricia J and Stern, David L}
}
@article {4649,
	title = {Morphological evolution through multiple cis-regulatory mutations at a single gene.},
	journal = {Nature},
	volume = {448},
	year = {2007},
	month = {2007 Aug 2},
	pages = {587-90},
	abstract = {<p>One central, and yet unsolved, question in evolutionary biology is the relationship between the genetic variants segregating within species and the causes of morphological differences between species. The classic neo-darwinian view postulates that species differences result from the accumulation of small-effect changes at multiple loci. However, many examples support the possible role of larger abrupt changes in the expression of developmental genes in morphological evolution. Although this evidence might be considered a challenge to a neo-darwinian micromutationist view of evolution, there are currently few examples of the actual genes causing morphological differences between species. Here we examine the genetic basis of a trichome pattern difference between Drosophila species, previously shown to result from the evolution of a single gene, shavenbaby (svb), probably through cis-regulatory changes. We first identified three distinct svb enhancers from D. melanogaster driving reporter gene expression in partly overlapping patterns that together recapitulate endogenous svb expression. All three homologous enhancers from D. sechellia drive expression in modified patterns, in a direction consistent with the evolved svb expression pattern. To test the influence of these enhancers on the actual phenotypic difference, we conducted interspecific genetic mapping at a resolution sufficient to recover multiple intragenic recombinants. This functional analysis revealed that independent genetic regions upstream of svb that overlap the three identified enhancers are collectively required to generate the D. sechellia trichome pattern. Our results demonstrate that the accumulation of multiple small-effect changes at a single locus underlies the evolution of a morphological difference between species. These data support the view that alleles of large effect that distinguish species may sometimes reflect the accumulation of multiple mutations of small effect at select genes.</p>
},
	keywords = {Alleles, Animals, Biological, Biological Evolution, Developmental, DNA-Binding Proteins, Drosophila, Drosophila Proteins, Enhancer Elements, Evolution, Gene Expression Regulation, Genes, Genetic, Genetic Speciation, Models, Molecular, Mutation, Recombination, Reporter, Transcription Factors},
	issn = {1476-4687},
	doi = {10.1038/nature05988},
	author = {McGregor, Alistair P and Orgogozo, Virginie and Delon, Isabelle and Zanet, Jennifer and Srinivasan, Dayalan G and Payre, Fran\c cois and Stern, David L}
}
