Pattern de pigmentation et contraintes développementales: les sites d'attachement des muscles du vol délimitent le trident thoracique de Drosophila melanogaster

International audienceIn their seminal paper published in 1979, Gould and Lewontin argued that some traits arise as by-products of the development of other structures and not for direct utility in themselves. We show here that this applies to the trident, a pigmentation pattern observed on the thorax of Drosophila melanogaster. Using reporter constructs, we show that the expression domain of several genes encoding pigmentation enzymes follows the trident shape. This domain is complementary to the expression pattern of stripe (sr), which encodes an essential transcription factor specifying flight muscle attachment sites. We demonstrate that sr limits the expression of these pigmentation enzyme genes to the trident by repressing them in its own expression domain, i.e. at the flight muscle attachment sites. We give evidence that repression of not only yellow but also other pigmentation genes, notably tan, is involved in the trident shape. The flight muscle attachment sites and sr expression patterns are remarkably conserved in dipterans reflecting the essential role of sr. Our data suggest that the trident is a by-product of flight muscle attachment site patterning that arose when sr was co-opted for the regulation of pigmentation enzyme coding genes

Phenotypic Plasticity in Drosophila Pigmentation Caused by Temperature Sensitivity of a Chromatin Regulator Network

Phenotypic plasticity is the ability of a genotype to produce contrasting phenotypes in different environments. Although many examples have been described, the responsible mechanisms are poorly understood. In particular, it is not clear how phenotypic plasticity is related to buffering, the maintenance of a constant phenotype against genetic or environmental variation. We investigate here the genetic basis of a particularly well described plastic phenotype: the abdominal pigmentation in female Drosophila melanogaster. Cold temperature induces a dark pigmentation, in particular in posterior segments, while higher temperature has the opposite effect. We show that the homeotic gene Abdominal-B (Abd-B) has a major role in the plasticity of pigmentation in the abdomen. Abd-B plays opposite roles on melanin production through the regulation of several pigmentation enzymes. This makes the control of pigmentation very unstable in the posterior abdomen, and we show that the relative spatio-temporal expression of limiting pigmentation enzymes in this region of the body is thermosensitive. Temperature acts on melanin production by modulating a chromatin regulator network, interacting genetically with the transcription factor bric-à-brac (bab), a target of Abd-B and Hsp83, encoding the chaperone Hsp90. Genetic disruption of this chromatin regulator network increases the effect of temperature and the instability of the pigmentation pattern in the posterior abdomen. Colocalizations on polytene chromosomes suggest that BAB and these chromatin regulators cooperate in the regulation of many targets, including several pigmentation enzymes. We show that they are also involved in sex comb development in males and that genetic destabilization of this network is also strongly modulated by temperature for this phenotype. Thus, we propose that phenotypic plasticity of pigmentation is a side effect reflecting a global impact of temperature on epigenetic mechanisms. Furthermore, the thermosensitivity of this network may be related to the high evolvability of several secondary sexual characters in the genus Drosophila

Recherche de facteurs céphalométriques prédictifs de l'efficacité d'une orthèse d'avancée mandibulaire (Bielles de Herbst) dans le traitement du syndrome d'apnées obstructives du sommeil de l'adulte

Ce travail rétrospectif recherche les facteurs prédictifs de l'efficacité d'une orthèse d'avancée mandibulaire (Bielles de Herbst) sur un échantillon de 8 patients souffrant d'un SAOS. Les patients ont été séparés en 2 groupes en fonction de l'évolution de leur IAH après 18 mois de traitement. L'étude des paramètres a été effectuée sur des téléradiographies à l'aide de l'analyse architecturale et structurale de Delaire et le relevé de points étudiant les tissus mous et la position de l'os hyoïde. Nous avons montré que les patients répondeurs ont les caractéristiques initiales suivantes par rapport aux patients non répondeurs : une tendance à des espaces pharyngés plus étroits, un os hyoïde plus postérieur par rapport au rachis, une tendance à la rétromandibulie par microcorpie, et surtout un angle mandibulaire significativement plus ouvert.ROUEN-BU Médecine-Pharmacie (765402102) / SudocPARIS-BIUM (751062103) / SudocSudocFranceF

The Paramount Role of Drosophila melanogaster in the Study of Epigenetics: From Simple Phenotypes to Molecular Dissection and Higher-Order Genome Organization

International audienceDrosophila melanogaster has played a paramount role in epigenetics, the study of changesin gene function inherited through mitosis or meiosis that are not due to changes in the DNA sequence.By analyzing simple phenotypes, such as the bristle position or cuticle pigmentation, asread-outs of regulatory processes, the identification of mutated genes led to the discovery of majorchromatin regulators. These are often conserved in distantly related organisms such as vertebratesor even plants. Many of them deposit, recognize, or erase post-translational modifications on histones(histone marks). Others are members of chromatin remodeling complexes that move, eject, orexchange nucleosomes. We review the role of D. melanogaster research in three epigenetic fields:Heterochromatin formation and maintenance, the repression of transposable elements by piRNAs,and the regulation of gene expression by the antagonistic Polycomb and Trithorax complexes. Wethen describe how genetic tools available in D. melanogaster allowed to examine the role of histonemarks and show that some histone marks are dispensable for gene regulation, whereas others playessential roles. Next, we describe how D. melanogaster has been particularly important in definingchromatin types, higher-order chromatin structures, and their dynamic changes during development.Lastly, we discuss the role of epigenetics in a changing environment

Data from: Phenotypic plasticity through transcriptional regulation of the evolutionary hotspot gene tan in Drosophila melanogaster

Phenotypic plasticity is the ability of a given genotype to produce different phenotypes in response to distinct environmental conditions. Phenotypic plasticity can be adaptive. Furthermore, it is thought to facilitate evolution. Although phenotypic plasticity is a widespread phenomenon, its molecular mechanisms are only beginning to be unravelled. Environmental conditions can affect gene expression through modification of chromatin structure, mainly via histone modifications, nucleosome remodelling or DNA methylation, suggesting that phenotypic plasticity might partly be due to chromatin plasticity. As a model of phenotypic plasticity, we study abdominal pigmentation of Drosophila melanogaster females, which is temperature sensitive. Abdominal pigmentation is indeed darker in females grown at 18°C than at 29°C. This phenomenon is thought to be adaptive as the dark pigmentation produced at lower temperature increases body temperature. We show here that temperature modulates the expression of tan (t), a pigmentation gene involved in melanin production. t is expressed 7 times more at 18°C than at 29°C in female abdominal epidermis. Genetic experiments show that modulation of t expression by temperature is essential for female abdominal pigmentation plasticity. Temperature modulates the activity of an enhancer of t without modifying compaction of its chromatin or level of the active histone mark H3K27ac. By contrast, the active mark H3K4me3 on the t promoter is strongly modulated by temperature. The H3K4 methyl-transferase involved in this process is likely Trithorax, as we show that it regulates t expression and the H3K4me3 level on the t promoter and also participates in female pigmentation and its plasticity. Interestingly, t was previously shown to be involved in inter-individual variation of female abdominal pigmentation in Drosophila melanogaster, and in abdominal pigmentation divergence between Drosophila species. Sensitivity of t expression to environmental conditions might therefore give more substrate for selection, explaining why this gene has frequently been involved in evolution of pigmentation

raw data Fig2

Expression of pigmentation genes in abdominal epidermis of female pharates and adults grown at 18°C and 29°

raw data S5Fig

IP H3/input, IP H3K27ac/Input and IP H3K4me3/IP H3 in abdominal epidermis of females grown at 18°C and 29°

The Expression of Pigmentation Enzymes Is Highly Dynamic and Modulated by Temperature

<div><p>(A–C) Dynamic expression of <i>ebony-LacZ</i> at 25 °C in the abdomen of pharate adults. Expression is first visible at the base of bristles around 90 h after puparium formation in (A) and then extends progressively from the anterior region of the segments to all epidermal cells within tergites (B and C).</p><p>(D–F) Dynamic expression at 25 °C of the tyrosine hydroxylase using <i>TH-Gal4</i> and <i>UAS-LacZ</i> transgenes. Expression starts earlier than <i>ebony-LacZ,</i> at the base of the large bristles on the posterior border of the segments. In (D), the bristles are not mature yet. The expression is then visible at the base of smaller bristles (E), and eventually in all epidermal cells (F). Note that the most posterior tergite, A7, does not show any strong staining.</p><p>(G–I) Dynamic expression of the tyrosine hydroxylase using <i>TH-Gal4</i> and <i>UAS-LacZ</i> transgenes in <i>Tab/+</i> females at 25 °C at 90 h after puparium formation. Thoraces have an increasing age from left to right, as revealed by the pigmentation at the base of bristles. The abdomen and thoraces shown within the same column do not necessarily have exactly the same age. See text for details.</p><p>(J) Expression of <i>ebony-LacZ</i> in female abdomen just before hatching at 20 °C. No strong expression is visible in A7.</p><p>(K) Expression of the tyrosine hydroxylase visualized using <i>TH-Gal4, UAS-LacZ</i> in female abdomen just before hatching at 20 °C. The expression in A7 is much more visible than at 25 °C. In limiting conditions, such as in females with three doses of <i>Abd-B</i> grown at 25 °C, the melanin almost completely disappears from A7 and remains only at the first sites of expression of <i>TH</i> associated with bristles (L).</p></div

raw data Fig8 and S6Fig

tan relative expression in control females and trx RNAi females, ChIP for H3K4me3 in control females and trx RNAi females, abdominal pigmentation quantification in control females (w1118) and females mutant for trx

<i>Abd-B</i> Interacts with Temperature in the Regulation of Melanin Production

<p>Shows the effect of variation of <i>Abd-B</i> dosage (1, 2, or 3 copy number) and temperature on melanin production in the lateral region of A6 (A), the median region of A6 (B), and the lateral region of A7 (C).</p