Drosophila Thorax Research Articles

The Tbx6 Transcription Factor Dorsocross Mediates Dpp Signaling to Regulate Drosophila Thorax Closure

Movement and fusion of separate cell populations are critical for several developmental processes, such as neural tube closure in vertebrates or embryonic dorsal closure and pupal thorax closure in Drosophila. Fusion failure results in an opening or groove on the body surface. Drosophila pupal thorax closure is an established model to investigate the mechanism of tissue closure. Here, we report the identification of T-box transcription factor genes Dorsocross (Doc) as Decapentaplegic (Dpp) targets in the leading edge cells of the notum in the late third instar larval and early pupal stages. Reduction of Doc in the notum region results in a thorax closure defect, similar to that in dpp loss-of-function flies. Nine genes are identified as potential downstream targets of Doc in regulating thorax closure by molecular and genetic screens. Our results reveal a novel function of Doc in Drosophila development. The candidate target genes provide new clues for unravelling the mechanism of collective cell movement.

A neural progenitor mitotic wave is required for asynchronous axon outgrowth and morphology.

Spatiotemporal mechanisms generating neural diversity are fundamental for understanding neural processes. Here, we investigated how neural diversity arises from neurons coming from identical progenitors. In the dorsal thorax of Drosophila, rows of mechanosensory organs originate from the division of sensory organ progenitor (SOPs). We show that in each row of the notum, an anteromedial located central SOP divides first, then neighbouring SOPs divide, and so on. This centrifugal wave of mitoses depends on cell-cell inhibitory interactions mediated by SOP cytoplasmic protrusions and Scabrous, a secreted protein interacting with the Delta/Notch complex. Furthermore, when this mitotic wave was reduced, axonal growth was more synchronous, axonal terminals had a complex branching pattern and fly behaviour was impaired. We show that the temporal order of progenitor divisions influences the birth order of sensory neurons, axon branching and impact on grooming behaviour. These data support the idea that developmental timing controls axon wiring neural diversity.

Proximate larval epidermal cell layer generates forces for Pupal thorax closure in Drosophila.

During tissue closures, such as embryonic dorsal closure in Drosophila melanogaster, a proximate extra-embryonic layer, amnioserosa, generates forces that drive migration of the flanking lateral embryonic epidermis, thereby zip-shutting the embryo. Arguably, this paradigm of tissue closure is also recapitulated in mammalian wound healing wherein proximate fibroblasts transform into contractile myofibroblasts, develop cell junctions, and form a tissue layer de novo: contraction of the latter then aids in wound closure. Given this parallelism between disparate exemplars, we posit a general principle of tissue closure via proximate cell layer-generated forces. Here, we have tested this hypothesis in pupal thorax closure wherein 2 halves of the presumptive adult thorax of Drosophila, the contralateral heminotal epithelia, migrate over an underlying larval epidermal cell layer. We show that the proximate larval epidermal cell layer promotes thorax closure by its active contraction, orchestrated by its elaborate actomyosin network-driven epithelial cell dynamics, cell delamination, and death-the latter being prefigured by the activation of caspases. Larval epidermal cell dynamics generate contraction forces, which when relayed to the flanking heminota-via their mutual integrin-based adhesions-mediate thorax closure. Compromising any of these contraction force-generating mechanisms in the larval epidermal cell layer slows down heminotal migration, while loss of its relay to the flanking heminota abrogates the thorax closure altogether. Mathematical modeling further reconciles the biophysical underpinning of this emergent mechanism of thorax closure. Revealing mechanism of thorax closure apart, these findings show conservation of an essential principle of a proximate cell layer-driven tissue closure.

Many ways to make darker flies: Intra- and interspecific variation in Drosophila body pigmentation components.

Body pigmentation is an evolutionarily diversified and ecologically relevant trait with substantial variation within and between species, and important roles in animal survival and reproduction. Insect pigmentation, in particular, provides some of the most compelling examples of adaptive evolution, including its ecological significance and genetic bases. Pigmentation includes multiple aspects of color and color pattern that may vary more or less independently, and can be under different selective pressures. We decompose Drosophila thorax and abdominal pigmentation, a valuable eco‐evo‐devo model, into distinct measurable traits related to color and color pattern. We investigate intra‐ and interspecific variation for those traits and assess its different sources. For each body part, we measured overall darkness, as well as four other pigmentation properties distinguishing between background color and color of the darker pattern elements that decorate each body part. By focusing on two standard D. melanogaster laboratory populations, we show that pigmentation components vary and covary in distinct manners depending on sex, genetic background, and temperature during development. Studying three natural populations of D. melanogaster along a latitudinal cline and five other Drosophila species, we then show that evolution of lighter or darker bodies can be achieved by changing distinct component traits. Our results paint a much more complex picture of body pigmentation variation than previous studies could uncover, including patterns of sexual dimorphism, thermal plasticity, and interspecific diversity. These findings underscore the value of detailed quantitative phenotyping and analysis of different sources of variation for a better understanding of phenotypic variation and diversification, and the ecological pressures and genetic mechanisms underlying them.

Temporal Order of Neural Progenitor Division Controls Neural Connectivity

Spatiotemporal mechanisms generating neural diversity are fundamental for understanding neural processes. Here, we investigated how neural connection diversity arises from neurons coming from identical progenitors. In the dorsal thorax of Drosophila, rows of mechanosensory organs originate from the division of sensory organ progenitor (SOPs). We show that in each row of the notum, a central SOP divides first, then neighboring SOPs divide, and so on. This centrifugal wave of mitoses depends on cell-cell inhibitory interactions mediated by SOP cytoplasmic protrusions and Scabrous, a secreted protein interacting with the Delta/Notch complex. When scabrous was downregulated, the mitotic wave was abolished, axonal growth was more synchronous, axonal terminals had a complex branching pattern and fly behavior was impaired. We propose that the temporal order of progenitor divisions influences the birth order of sensory neurons which is critical for correct axon wiring and appropriate grooming behavior, supporting the idea that developmental timing controls neural connectivity.

A More Standardized Method for Imaging and Measuring Drosophila Thorax Length Using ImageJ

Thorax measurements are important metrics of Drosophila fitness and are often correlated with key life-history traits, such as lifespan and fecundity. Therefore, thorax length is a widely used measure in studies of genetic variation and plasticity in response to environmental alterations. However, the lack of fixed landmarks means that thorax measurements can sometimes be inconsistent and highly variable. Here, we outline a dorsal bristle-guided method of thorax measurements, which we could use to draw a reliable and repeatable line from the thorax scutellum to the anterior thorax edge. We analyzed and compared this bristle-guided marker method to a non-landmark-based thorax measurement in a set of measures of female and male D. melanogaster. We found that the bristle-guided method exhibited significantly less variation between technical replicates than the non-landmark-based measure., [摘要]胸部测量是重要的指标果蝇健身，并经常和按键寿命相关-历史特质，如寿命和繁殖力。因此，胸部长度是研究遗传变异和可塑性以响应环境变化的广泛使用的量度。然而，缺乏固定地标意味着胸部测量有时可能不一致且高度可变。在这里，我们勾勒出一个背毛-的胸部测量，我们可以用它来借鉴胸部盾片的前胸部边缘的可靠和可重复线路引导方法。我们分析并比较了这种刷毛引导标记方法与非标记方法-基于一组的男性和女性的胸部测量测量果蝇。我们发现，刷毛引导的方法具有技术复制比非地标之间的显著变化较小-基于市场的措施。[背景]胸测量在果蝇是一个重要和广泛使用的生活史，可塑性的研究指标，和遗传（例如，Imasheva等，1999;贝格兰等，2008; Lafuente的等，2018）。这是由于胸部尺寸和健身的指标之间的公认关系，如繁殖力和寿命（哈森等人。，1992）。许多研究中的常规胸部测量选择从盾片尖端到胸部边缘进行测量。然而，与其他组的形态测量不同（例如，在翅膀上进行的那些，其中静脉和静脉交界处形成清晰的锚点和界标），胸部提供较少的明显固定和可识别的边缘点。这会使胸部测量更具挑战性，并且可能在不同的研究中不标准化。例如，测量的角度可能是任意的，这会在重复测量之间引入很大的变化。在这里，我们概述了一个协议，用于根据横向观察时位于胸部前端的固定刷毛点进行一致的胸部长度测量。这个固定点允许从盾片可以得出一个可重复的角度，从而显著改善了当相比于非地标跨复制测量稠度-引导方法。

Dysfunction of LSD-1 induces JNK signaling pathway-dependent abnormal development of thorax and apoptosis cell death in Drosophila melanogaster

Perilipins are evolutionarily conserved from insects to mammals. Lipid storage droplet-1 (LSD-1) is a member of the lipid droplet's surface-binding protein family and counterpart to mammalian perilipin 1. The role of LSD-1 has already been reported in lipid metabolism of Drosophila. However, the function of this gene during specific tissue development is still under investigation. Here, we found that LSD-1 is expressed in the notum of the wing imaginal disc, and notum-specific knockdown of Lsd-1 by pannir-GAL4 driver leads to split thorax phenotype in adults, suggesting an essential role of LSD-1 in development of Drosophila thorax. As overexpression of JNK homolog, bsk (basket) suppresses Lsd-1 knockdown phenotype, the role of LSD-1 in thorax development was proved to be dependent on the activity of the Drosophila c-Jun N-terminal kinase (JNK). The puckered (puc) expression led to significant decrease in the JNK activity in wing discs of Lsd-1 knockdown flies. In addition, we also detected that depletion of Lsd-1 enhances apoptotic cell death in the wing notum area. Taken together, these data demonstrated that LSD-1 functions in Drosophila thorax development by regulating JNK pathway.

High expression of A-type lamin in the leading front is required for Drosophila thorax closure

Tissue closure involves the coordinated unidirectional movement of a group of cells without loss of cell–cell contact. However, the molecular mechanisms controlling the tissue closure are not fully understood. Here, we demonstrate that Lamin C, the sole A-type lamin in Drosophila, contributes to the process of thorax closure in pupa. High expression of Lamin C was observed at the leading front of the migrating wing imaginal discs. Live imaging analysis revealed that knockdown of Lamin C in the thorax region affected the coordinated movement of the leading front, resulting in incomplete tissue fusion required for formation of the adult thorax. The closure defect due to knockdown of Lamin C correlated with insufficient accumulation of F-actin at the front. Our study indicates a link between A-type lamin and the cell migration behavior during tissue closure.

DNA Underreplication in the Majority of Nuclei in the Drosophila Melanogaster Thorax: Evidence from Suur and Flow Cytometry

The discovery of endoreduplication in the majority of cells of the thorax of Drosophila has implications for genomics, transcriptome levels, chromatin structure and life history of these model insects. The ratio of 2C/4C DNA amounts is 2.00 for nuclei from the head, yet is 1.75 and 1.83 for nuclei from the thorax of wild type and suppressor of underreplication (SuUR) strains, respectively. The latter ratios reflect underreplication in the majority of nuclei from the thorax, which is only partially suppressed in the SuUR strain. The effect is age-dependent. Thoracic 4C DNA is significantly more underreplicated in the nuclei of 10 day old than newly emerged flies. The consequences of underreplication for the majority of thoracic cell nuclei, likely mimic those in highly endoreduplicated polytene salivary and nurse cell nuclei, which would affect expression levels in genomic, transcriptomic, methalomic and other studies based wholly or in part on Drosophila thoracic nuclei.

Drosophila DREF acting via the JNK pathway is required for thorax development

The Drosophila Jun N-terminal kinase (JNK) gene basket (bsk) promoter contains a DNA replication-related element (DRE)-like sequence, raising the possibility of regulation by the DNA replication-related element-binding factor (DREF). Chromatin immunoprecipitation assays with anti-DREF IgG showed the bsk gene promoter region to be effectively amplified. Luciferase transient expression assays revealed the DRE-like sequence to be important for bsk gene promoter activity, and knockdown of DREF decreased the bsk mRNA level and the bsk gene promoter activity. Furthermore, knockdown of DREF in the notum compartment of wing discs by pannier-GAL4 and UAS-DREFIR resulted in a split thorax phenotype. Monitoring of JNK activity in the wing disc by LacZ expression in a puckered (puc)-LacZ enhancer trap line revealed the reduction in DREF knockdown clones. These findings indicate that DREF is involved in regulation of Drosophila thorax development via actions on the JNK pathway.

The MYST-Containing Protein Chameau Is Required for Proper Sensory Organ Specification during Drosophila Thorax Morphogenesis

The adult thorax of Drosophila melanogaster is covered by a stereotyped pattern of mechanosensory bristles called macrochaetes. Here, we report that the MYST containing protein Chameau (Chm) contributes to the establishment of this pattern in the most dorsal part of the thorax. Chm mutant pupae present extra-dorsocentral (DC) and scutellar (SC) macrochaetes, but a normal number of the other macrochaetes. We provide evidences that chm restricts the singling out of sensory organ precursors from proneural clusters and genetically interacts with transcriptional regulators involved in the regulation of achaete and scute in the DC and SC proneural cluster. This function of chm likely relies on chromatin structure regulation since a protein with a mutation in the conserved catalytic site fails to rescue the formation of supernumerary DC and SC bristles in chm mutant flies. This is further supported by the finding that mutations in genes encoding chromatin modifiers and remodeling factors, including Polycomb group (PcG) and Trithorax group (TrxG) members, dominantly modulate the penetrance of chm extra bristle phenotype. These data support a critical role for chromatin structure modulation in the establishment of the stereotyped sensory bristle pattern in the fly thorax.

Myosin Heavy Chain Isoforms Influence the Magnitude of Stretch Activation in Drosophila Muscles

The stretch activation (SA) mechanism, a general property of all muscle types, is most prominent in muscles that generate power through cyclical contractions, such as insect indirect flight muscles (IFM) and vertebrate cardiac muscles. SA is defined as phase 3, a delayed tension increase, of the tension transient following a muscle stretch. We are testing our hypothesis that myosin heavy chain isoforms help set SA magnitude and hence power generating ability in different muscle types. The Drosophila thorax contains two muscle types, IFMs and jump muscles. In IFMs, the magnitude of SA is great enough to enable net positive power generation when it is fully calcium activated. In contrast, jump muscles display very little stretch activation and cannot generate net positive power when fully activated. We found that when an embryonic myosin isoform (EMB) is transgenically expressed in the jump muscle, the muscle is transformed and behaves like a moderately stretch-activatable muscle. The transformed muscle can now generate positive power and SA magnitude is increased by ∼60% at 0mM Pi and ∼350% at 16mM Pi. This shows that SA magnitude is influenced by myosin isoforms. We found that power generation is [Pi] dependent as ≥ 2mM Pi is required for power production in jump muscles expressing the EMB isoform. Expressing the IFM isoform in jump muscles did not enable positive power generation or increase SA magnitude. To further test our hypothesis, we are expressing the jump myosin isoform in IFMs to determine if this reduces IFM SA magnitude. We conclude that myosin isoforms can influence the magnitude of SA, but are not the only mechanism responsible for natural differences in SA magnitude.

Intertissue Mechanical Stress Affects Frizzled-Mediated Planar Cell Polarity in the Drosophila Notum Epidermis

Frizzled/planar cell polarity (Fz/PCP) signaling controls the orientation of sensory bristles and cellular hairs (trichomes) along the anteroposterior axis of the Drosophila thorax (notum). A subset of the trichome-producing notum cells differentiate as "tendon cells," serving as attachment sites for the indirect flight muscles (IFMs) to the exoskeleton. Through the analysis of chascon (chas), a gene identified by its ability to disrupt Fz/PCP signaling under overexpression conditions, and jitterbug (jbug)/filamin, we show that maintenance of anteroposterior planar polarization requires the notum epithelia to balance mechanical stress generated by the attachment of the IFMs. chas is expressed in notum tendon cells, and its loss of function disturbs cellular orientation at and near the regions where IFMs attach to the epidermis. This effect is independent of the Fz/PCP and fat/dachsous systems. The chas phenotype arises during normal shortening of the IFMs and is suppressed by genetic ablation of the IFMs. chas acts through jbug/filamin and cooperates with MyosinII to modulate the mechanoresponse of notum tendon cells. These observations support the notion that the ability of epithelia to respond to mechanical stress generated by one or more interactions with other tissues during development and organogenesis influences the maintenance of its shape and PCP features.

Notch Signaling: Filopodia Dynamics Confer Robustness

Though usually thought of as mediating communication between adjacent cells, Notch-Delta signaling can take place over a longer range through cellular processes known as 'filopodia'. A recent study shows how the dynamics of filopodia can confer robustness to Notch-Delta dependent patterning.

Prepatterning the Drosophila notum: The three genes of the iroquois complex play intrinsically distinct roles

The Drosophila thorax exhibits 11 pairs of large sensory organs (macrochaetes) identified by their unique position. Remarkably precise, this pattern provides an excellent model system to study the genetic basis of pattern formation. In imaginal wing discs, the achaete–scute proneural genes are expressed in clusters of cells that prefigure the positions of each macrochaete. The activities of prepatterning genes provide positional cues controlling this expression pattern. The three homeobox genes clustered in the iroquois complex (araucan, caupolican and mirror) are such prepattern genes. mirror is generally characterized as performing functions predominantly different from the other iroquois genes. Conversely, araucan and caupolican are described in previous studies as performing redundant functions in most if not all processes in which they are involved. We have addressed the question of the specific role of each iroquois gene in the prepattern of the notum and we clearly demonstrate that they are intrinsically different in their contribution to this process: caupolican and mirror, but not araucan, are required for the neural patterning of the lateral notum. However, when caupolican and/or mirror expression is reduced, araucan loss of function has an effect on thoracic bristles development. Moreover, the overexpression of araucan is able to rescue caupolican loss of function. We conclude that, although retaining some common functionalities, the Drosophila iroquois genes are in the process of diversification. In addition, caupolican and mirror are required for stripe expression and, therefore, to specify the muscular attachment sites prepattern. Thus, caupolican and mirror may act as common prepattern genes for all structures in the lateral notum.

The origin and evolution of stereotyped patterns of macrochaetes on the nota of cyclorraphous Diptera

A long-standing problem in evolutionary biology is how genetic variation arises within populations and evolves to make species anatomically different. Many of the morphological differences in body plans between animal groups are thought to result from changes in gene expression during development. The rules governing the structure and evolution of cis-regulatory gene sequences are unknown, however, and the evolution of traits between closely related species remains relatively unexplored at a molecular level. To study the evolution of gene regulation, it is necessary to find a tractable trait that varies between species and for which the genetic regulation is well known in at least one of the species. The stereotyped, two-dimensional pattern of bristles on the thorax of Drosophila has been intensively investigated and is due to a precise spatial expression of proneural genes. Other species of flies have different bristle patterns and so comparisons between them provide a good paradigm for the study of changes in gene regulation. Here, we review the current state of understanding of these changes.

Distinct Roles for Two Receptor Tyrosine Kinases in Epithelial Branching Morphogenesis in Drosophila

Branching morphogenesis is a widespread mechanism used to increase the surface area of epithelial organs. Many signaling systems steer development of branched organs, but it is still unclear which cellular processes are regulated by the different pathways. We have used the development of the air sacs of the dorsal thorax of Drosophila to study cellular events and their regulation via cell-cell signaling. We find that two receptor tyrosine kinases play important but distinct roles in air sac outgrowth. Fgf signaling directs cell migration at the tip of the structure, while Egf signaling is instrumental for cell division and cell survival in the growing epithelial structure. Interestingly, we find that Fgf signaling requires Ras, the Mapk pathway, and Pointed to direct migration, suggesting that both cytoskeletal and nuclear events are downstream of receptor activation. Ras and the Mapk pathway are also needed for Egf-regulated cell division/survival, but Pointed is dispensable.

E. B. Lewis and the bithorax complex: part I.

IN 1995, Edward B. Lewis shared in the Nobel Prize in Physiology or Medicine for his work on the bithorax complex (BX-C), a gene cluster that controls the identities of body segments in the abdomen and posterior thorax of Drosophila. Over a period of some 50 years, Lewis defined the functions and

Asymmetric cell division: plane but not simple.

The polarity of sensory bristles on the thorax of Drosophila is linked to the orientation of the asymmetric cell divisions that partition cell fate determinants in this lineage. The orientation of these divisions is under the control of the Frizzled pathway that generates planar polarity in a number of cell types.

Multiple Roles for four-jointed in Planar Polarity and Limb Patterning

Insect cuticles have been a model system for the study of planar polarity for many years and a number of genes required for this process have been identified. These genes organise the polarised arrangement of hairs on the legs, wings, thorax, and abdomen of adult Drosophila. It has previously been shown that four-jointed is involved in planar polarity decisions in the eye as well as proximal distal leg and wing development. We now present evidence that four-jointed is expressed in a gradient through the developing wing and show that it is required for planar polarity determination in both the wing and the abdomen. Clones of cells either lacking or ectopically expressing four-jointed cause both autonomous and nonautonomous repolarisation of hairs in these tissues. We propose that the inferred four-jointed expression gradient is important for planar polarity establishment and that local inversions of the gradient by the clones are the probable cause of the observed polarity phenotypes. In addition we observe defects in wing vein development. The subtle phenotypes of mutant flies, and the diverse patterning processes in which it is involved, suggest that four-jointed may act as a modifier of the activity of multiple other signalling factors.