RESUMO

Evolutionary analyses have estimated that ∼60% of nucleotides in intergenic regions of the Drosophila melanogaster genome are functionally relevant, suggesting that regulatory information may be encoded more densely in intergenic regions than has been revealed by most functional dissections of regulatory DNA. Here, we approached this issue through a functional dissection of the regulatory region of the gene shavenbaby (svb). Most of the ∼90 kb of this large regulatory region is highly conserved in the genus Drosophila, though characterized enhancers occupy a small fraction of this region. By analyzing the regulation of svb in different contexts of Drosophila development, we found that the regulatory information that drives svb expression in the abdominal pupal epidermis is organized in a different way than the elements that drive svb expression in the embryonic epidermis. While in the embryonic epidermis svb is activated by compact enhancers separated by large inactive DNA regions, svb expression in the pupal epidermis is driven by regulatory information distributed over broader regions of svb cis-regulatory DNA. In the same vein, we observed that other developmental genes also display a dense distribution of putative regulatory elements in their regulatory regions. Furthermore, we found that a large percentage of conserved noncoding DNA of the Drosophila genome is contained within regions of open chromatin. These results suggest that part of the evolutionary constraint on noncoding DNA of Drosophila is explained by the density of regulatory information, which may be greater than previously appreciated.

Assuntos

Proteínas de Drosophila , Drosophila , Animais , Drosophila/metabolismo , Fatores de Transcrição/metabolismo , Drosophila melanogaster/genética , Drosophila melanogaster/metabolismo , Proteínas de Ligação a DNA/genética , Proteínas de Drosophila/genética , Proteínas de Drosophila/metabolismo , Regulação da Expressão Gênica no Desenvolvimento , DNA , DNA Intergênico/genética , DNA Intergênico/metabolismo , Elementos Facilitadores Genéticos

RESUMO

Despite considerable progress in recent decades in dissecting the genetic causes of natural morphological variation, there is limited understanding of how variation within species ultimately contributes to species differences. We have studied patterning of the non-sensory hairs, commonly known as "trichomes," on the dorsal cuticle of first-instar larvae of Drosophila. Most Drosophila species produce a dense lawn of dorsal trichomes, but a subset of these trichomes were lost in D. sechellia and D. ezoana due entirely to regulatory evolution of the shavenbaby (svb) gene. Here, we describe intraspecific variation in dorsal trichome patterns of first-instar larvae of D. virilis that is similar to the trichome pattern variation identified previously between species. We found that a single large effect QTL, which includes svb, explains most of the trichome number difference between two D. virilis strains and that svb expression correlates with the trichome difference between strains. This QTL does not explain the entire difference between strains, implying that additional loci contribute to variation in trichome numbers. Thus, the genetic architecture of intraspecific variation exhibits similarities and differences with interspecific variation that may reflect differences in long-term and short-term evolutionary processes.

Assuntos

Proteínas de Ligação a DNA/genética , Proteínas de Drosophila/genética , Drosophila/genética , Larva/anatomia & histologia , Locos de Características Quantitativas , Fatores de Transcrição/genética , Animais , Drosophila/anatomia & histologia , Feminino , Masculino , Fenótipo , Polimorfismo Genético , Sequências Reguladoras de Ácido Nucleico/genética , Especificidade da Espécie