Craniofacial diversification in the domestic pigeon and the evolution of the avian skull.

A central question in evolutionary developmental biology is how highly conserved developmental systems can generate the remarkable phenotypic diversity observed among distantly related species. In part, this paradox reflects our limited knowledge about the potential for species to both respond to selection and generate novel variation. Consequently, the developmental links between small-scale microevolutionary variations within populations to larger macroevolutionary patterns among species remain unbridged. Domesticated species, such as the pigeon, are unique resources for addressing this question, because a history of strong artificial selection has significantly increased morphological diversity, offering a direct comparison of the developmental potential of a single species to broader evolutionary patterns. Here, we demonstrate that patterns of variation and covariation within and between the face and braincase in domesticated breeds of the pigeon are predictive of avian cranial evolution. These results indicate that selection on variation generated by a conserved developmental system is sufficient to explain the evolution of crania as different in shape as the albatross or eagle, parakeet or hummingbird. These 'rules' of cranio-facial variation are a common pattern in the evolution of a broad diversity of vertebrate species and may ultimately reflect structural limitations of a shared embryonic bauplan on functional variation

Epistatic and Combinatorial Effects of Pigmentary Gene Mutations in the Domestic Pigeon

SummaryUnderstanding the molecular basis of phenotypic diversity is a critical challenge in biology, yet we know little about the mechanistic effects of different mutations and epistatic relationships among loci that contribute to complex traits. Pigmentation genetics offers a powerful model for identifying mutations underlying diversity and for determining how additional complexity emerges from interactions among loci. Centuries of artificial selection in domestic rock pigeons (Columba livia) have cultivated tremendous variation in plumage pigmentation through the combined effects of dozens of loci. The dominance and epistatic hierarchies of key loci governing this diversity are known through classical genetic studies [1–6], but their molecular identities and the mechanisms of their genetic interactions remain unknown. Here we identify protein-coding and cis-regulatory mutations in Tyrp1, Sox10, and Slc45a2 that underlie classical color phenotypes of pigeons and present a mechanistic explanation of their dominance and epistatic relationships. We also find unanticipated allelic heterogeneity at Tyrp1 and Sox10, indicating that color variants evolved repeatedly though mutations in the same genes. These results demonstrate how a spectrum of coding and regulatory mutations in a small number of genes can interact to generate substantial phenotypic diversity in a classic Darwinian model of evolution [7]

Analysis of Microsatellite Variation in Drosophila melanogaster with Population-Scale Genome Sequencing

Genome sequencing technologies promise to revolutionize our understanding of genetics, evolution, and disease by making it feasible to survey a broad spectrum of sequence variation on a population scale. However, this potential can only be realized to the extent that methods for extracting and interpreting distinct forms of variation can be established. The error profiles and read length limitations of early versions of next-generation sequencing technologies rendered them ineffective for some sequence variant types, particularly microsatellites and other tandem repeats, and fostered the general misconception that such variants are inherently inaccessible to these platforms. At the same time, tandem repeats have emerged as important sources of functional variation. Tandem repeats are often located in and around genes, and frequent mutations in their lengths exert quantitative effects on gene function and phenotype, rapidly degrading linkage disequilibrium between markers and traits. Sensitive identification of these variants in large-scale next-gen sequencing efforts will enable more comprehensive association studies capable of revealing previously invisible associations. We present a population-scale analysis of microsatellite repeats using whole-genome data from 158 inbred isolates from the Drosophila Genetics Reference Panel, a collection of over 200 extensively phenotypically characterized isolates from a single natural population, to uncover processes underlying repeat mutation and to enable associations with behavioral, morphological, and life-history traits. Analysis of repeat variation from next-generation sequence data will also enhance studies of genome stability and neurodegenerative diseases

Low-complexity regions within protein sequences have position-dependent roles

<p>Abstract</p> <p>Background</p> <p>Regions of protein sequences with biased amino acid composition (so-called Low-Complexity Regions (LCRs)) are abundant in the protein universe. A number of studies have revealed that i) these regions show significant divergence across protein families; ii) the genetic mechanisms from which they arise lends them remarkable degrees of compositional plasticity. They have therefore proved difficult to compare using conventional sequence analysis techniques, and functions remain to be elucidated for most of them. Here we undertake a systematic investigation of LCRs in order to explore their possible functional significance, placed in the particular context of Protein-Protein Interaction (PPI) networks and Gene Ontology (GO)-term analysis.</p> <p>Results</p> <p>In keeping with previous results, we found that LCR-containing proteins tend to have more binding partners across different PPI networks than proteins that have no LCRs. More specifically, our study suggests i) that LCRs are preferentially positioned towards the protein sequence extremities and, in contrast with centrally-located LCRs, such terminal LCRs show a correlation between their lengths and degrees of connectivity, and ii) that centrally-located LCRs are enriched with transcription-related GO terms, while terminal LCRs are enriched with translation and stress response-related terms.</p> <p>Conclusions</p> <p>Our results suggest not only that LCRs may be involved in flexible binding associated with specific functions, but also that their positions within a sequence may be important in determining both their binding properties and their biological roles.</p

Variation of BMP3 Contributes to Dog Breed Skull Diversity

Since the beginnings of domestication, the craniofacial architecture of the domestic dog has morphed and radiated to human whims. By beginning to define the genetic underpinnings of breed skull shapes, we can elucidate mechanisms of morphological diversification while presenting a framework for understanding human cephalic disorders. Using intrabreed association mapping with museum specimen measurements, we show that skull shape is regulated by at least five quantitative trait loci (QTLs). Our detailed analysis using whole-genome sequencing uncovers a missense mutation in BMP3. Validation studies in zebrafish show that Bmp3 function in cranial development is ancient. Our study reveals the causal variant for a canine QTL contributing to a major morphologic trait

Bayesian Statistical Studies of the Ramachandran Distribution

We describe a method for the generation of knowledge-based potentials and apply it to the observed torsional angles of known protein structures. The potential is derived using Bayesian reasoning, and is useful as a prior for further such reasoning in the presence of additional data. The potential takes the form of a probability density function, which is described by a small number of coefficients with the number of necessary coefficients determined by tests based on statistical significance and entropy. We demonstrate the methods in deriving one such potential corresponding to two dimensions, the Ramachandran plot. In contrast to traditional histogram-based methods, the function is continuous and differentiable. These properties allow us to use the function as a force term in the energy minimization of appropriately described structures. The method can easily be extended to other observable angles and higher dimensions, or to include sequence dependence and should find applications in structure determination and validation.

Contrasting Evolutionary Dynamics of the Developmental Regulator PAX9, among Bats, with Evidence for a Novel Post-Transcriptional Regulatory Mechanism

Morphological evolution can be the result of natural selection favoring modification of developmental signaling pathways. However, little is known about the genetic basis of such phenotypic diversity. Understanding these mechanisms is difficult for numerous reasons, yet studies in model organisms often provide clues about the major developmental pathways involved. The paired-domain gene, PAX9, is known to be a key regulator of development, particularly of the face and teeth. In this study, using a comparative genetics approach, we investigate PAX9 molecular evolution among mammals, focusing on craniofacially diversified (Phyllostomidae) and conserved (Vespertilionidae) bat families, and extend our comparison to other orders of mammal. Open-reading frame analysis disclosed signatures of selection, in which a small percentage of residues vary, and lineages acquire different combinations of variation through recurrent substitution and lineage specific changes. A few instances of convergence for specific residues were observed between morphologically convergent bat lineages. Bioinformatic analysis for unknown PAX9 regulatory motifs indicated a novel post-transcriptional regulatory mechanism involving a Musashi protein. This regulation was assessed through fluorescent reporter assays and gene knockdowns. Results are compatible with the hypothesis that the number of Musashi binding-elements in PAX9 mRNA proportionally regulates protein translation rate. Although a connection between morphology and binding element frequency was not apparent, results indicate this regulation would vary among craniofacially divergent bat species, but b

Changes in repeat length typically occur in the form of insertions and deletions of whole repeated units.

<p>The plotted dataset consisted of repeats that were at least 90% pure, with a minimum reference repeat length of 13, 20, 23, and 27 bases for (A) 2mers, (B) 3mers, (C) 4mers, and (D) 5mers, respectively. Genotypes were determined if there were at least two scorable reads and a read was scored if it spanned the repeat region with 3 or more matching flank bases on either side of the repeat.</p