Patterning Muscles Using Organizers: Larval Muscle Templates and Adult Myoblasts Actively Interact to Pattern the Dorsal Longitudinal Flight Muscles of Drosophila

Pattern formation in muscle development is often mediated by special cells called muscle organizers. During metamorphosis in Drosophila, a set of larval muscles function as organizers and provide scaffolding for the development of the dorsal longitudinal flight muscles. These organizers undergo defined morphological changes and dramatically split into templates as adult fibers differentiate during pupation. We have investigated the cellular mechanisms involved in the use of larval fibers as templates. Using molecular markers that label myoblasts and the larval muscles themselves, we show that splitting of the larval muscles is concomitant with invasion by imaginal myoblasts and the onset of differentiation. We show that the Erect wing protein, an early marker of muscle differentiation, is not only expressed in myoblasts just before and after fusion, but also in remnant larval nuclei during muscle differentiation. We also show that interaction between imaginal myoblasts and larval muscles is necessary for transformation of the larval fibers. In the absence of imaginal myoblasts, the earliest steps in metamorphosis, such as the escape of larval muscles from histolysis and changes in their innervation, are normal. However, subsequent events, such as the splitting of these muscles, fail to progress. Finally, we show that in a mutant combination, null for Erect wing function in the mesoderm, the splitting of the larval muscles is aborted. These studies provide a genetic and molecular handle for the understanding of mechanisms underlying the use of muscle organizers in muscle patterning. Since the use of such organizers is a common theme in myogenesis in several organisms, it is likely that many of the processes that we describe are conserved

Hox Genes Regulate Muscle Founder Cell Pattern Autonomously and Regulate Morphogenesis Through Motor Neurons

The differentiation of myoblasts to form functional muscle fibers is a consequence of interactions between the mesoderm and ectoderm. The authors examine the role of segment identity in directing these interactions by studying the role of Hox genes in patterning adult muscles in Drosophila. Using the `four-winged fly' to remove Ultrabithorax function in the developing adult, the authors alter the identity of the ectoderm of the third thoracic segment towards the second and show that this is sufficient to inductively alter most properties of the mesoderm—myoblast number, molecular diversity, and migration pattern—to that of the second thoracic segment. Not all aspects of myogenesis are determined by the segment identity of the ectoderm. The autonomous identity of the mesoderm is important for choosing muscle founder cells in the correct segmental pattern. The authors show this by removal of the function of Antennapedia, the Hox gene expressed in the mesoderm of the third thoracic segment. This results in the transformation of founder cells to a second-thoracic pattern. The authors also report a role for the nervous system in later aspects of muscle morphogenesis by specifically altering Ultrabithorax gene expression in motor neurons. Thus, ectoderm and mesoderm segment identities collaborate to direct muscle differentiation by affecting distinct aspects of the process

A spectrum of genes expressed during early stages of rice panicle and flower development

To unravel gene expression patterns during rice inflorescence development, particularly at early stages of panicle and floral organ specification, we have characterized random cloned cDNAs from developmental-stage-specific libraries. cDNA libraries were constructed from rice panicles at the stage of branching and flower primordia specification or from panicles undergoing floral organogenesis. Partial sequence analysis and expression patterns of some of these random cDNA clones from these two rice panicle libraries are presented. Sequence comparisons with known DNA sequences in databases reveal that approximately sixtyeight per cent of these expressed rice genes show varying degrees of similarity to genes in other species with assigned functions. In contrast, thirtytwo per cent represent uncharacterized genes. cDNAs reported here code for potential rice homologues of housekeeping molecules, regulators of gene expression, and signal transduction molecules. They comprise both single-copy and multicopy genes, and genes expressed differentially, both spatially and temporally, during rice plant development. New rice cDNAs requiring specific mention are those with similarity to COP1, a regulator of photomorphogenesis inArabidopsis; sequence-specific DNA binding plant proteins like AP2-domain-containing factors; genes that specify positional information in shoot meristems like leucine-rich-repeat-containing receptor kinases; regulators of chromatin structure like Polycomb domain protein; and also proteins induced by abiotic stresses

Drosophila Heartless Acts with Heartbroken/Dof in Muscle Founder Differentiation

The formation of a multi-nucleate myofibre is directed, in Drosophila, by a founder cell. In the embryo, founders are selected by Notch-mediated lateral inhibition, while during adult myogenesis this mechanism of selection does not appear to operate. We show, in the muscles of the adult abdomen, that the Fibroblast growth factor pathway mediates founder cell choice in a novel manner. We suggest that the developmental patterns of Heartbroken/Dof and Sprouty result in defining the domain and timing of activation of the Fibroblast growth factor receptor Heartless in specific myoblasts, thereby converting them into founder cells. Our results point to a way in which muscle differentiation could be initiated and define a critical developmental function for Heartbroken/Dof in myogenesis

Dendritic Targeting in the Leg Neuropil of Drosophila: The Role of Midline Signalling Molecules in Generating a Myotopic Map

During development of the Drosophila motor system, global guidance cues control and coordinate the targeting of both input and output elements of the neural system

Drosophila Protein interaction Map (DPiM): A paradigm for metazoan protein complex interactions

Proteins perform essential cellular functions as part of protein complexes, often in conjunction with RNA, DNA, metabolites and other small molecules. The genome encodes thousands of proteins but not all of them are expressed in every cell type; and expressed proteins are not active at all times. Such diversity of protein expression and function accounts for the level of biological intricacy seen in nature. Defining protein-protein interactions in protein complexes, and establishing the when, what and where of potential interactions, is therefore crucial to understanding the cellular function of any protein—especially those that have not been well studied by traditional molecular genetic approaches. We generated a large-scale resource of affinity-tagged expression-ready clones and used co-affinity purification combined with tandem mass-spectrometry to identify protein partners of nearly 5,000 Drosophila melanogaster proteins. The resulting protein complex “map” provided a blueprint of metazoan protein complex organization. Here we describe how the map has provided valuable insights into protein function in addition to generating hundreds of testable hypotheses. We also discuss recent technological advancements that will be critical in addressing the next generation of questions arising from the map

Identification and analysis of a glutamatergic local interneuron lineage in the adult Drosophila olfactory system

BACKGROUND: The antennal lobe of Drosophila is perhaps one of the best understood neural circuits, because of its well-described anatomical and functional organization and ease of genetic manipulation. Olfactory lobe interneurons - key elements of information processing in this network - are thought to be generated by three identified central brain neuroblasts, all of which generate projection neurons. One of these neuroblasts, located lateral to the antennal lobe, also gives rise to a population of local interneurons, which can either be inhibitory (GABAergic) or excitatory (cholinergic). Recent studies of local interneuron number and diversity suggest that additional populations of this class of neurons exist in the antennal lobe. This implies that other, as yet unidentified, neuroblast lineages may contribute a substantial number of local interneurons to the olfactory circuitry of the antennal lobe. RESULTS: We identified and characterized a novel glutamatergic local interneuron lineage in the Drosophila antennal lobe. We used MARCM (mosaic analysis with a repressible cell marker) and dual-MARCM clonal analysis techniques to identify this novel lineage unambiguously, and to characterize interneurons contained in the lineage in terms of structure, neurotransmitter identity, and development. We demonstrated the glutamatergic nature of these interneurons by immunohistochemistry and use of an enhancer-trap strain, which reports the expression of the Drosophila vesicular glutamate transporter (DVGLUT). We also analyzed the neuroanatomical features of these local interneurons at single-cell resolution, and documented the marked diversity in their antennal lobe glomerular innervation patterns. Finally, we tracked the development of these dLim-1 and Cut positive interneurons during larval and pupal stages. CONCLUSIONS: We have identified a novel neuroblast lineage that generates neurons in the antennal lobe of Drosophila. This lineage is remarkably homogeneous in three respects. All of the progeny are local interneurons, which are uniform in their glutamatergic neurotransmitter identity, and form oligoglomerular or multiglomerular innervations within the antennal lobe. The identification of this novel lineage and the elucidation of the innervation patterns of its local interneurons (at single cell resolution) provides a comprehensive cellular framework for emerging studies on the formation and function of potentially excitatory local interactions in the circuitry of the Drosophila antennal lobe

Metamorphosis of an identified serotonergic neuron in the Drosophila olfactory system.

BACKGROUND: Odors are detected by sensory neurons that carry information to the olfactory lobe where they connect to projection neurons and local interneurons in glomeruli: anatomically well-characterized structures that collect, integrate and relay information to higher centers. Recent studies have revealed that the sensitivity of such networks can be modulated by wide-field feedback neurons. The connectivity and function of such feedback neurons are themselves subject to alteration by external cues, such as hormones, stress, or experience. Very little is known about how this class of central neurons changes its anatomical properties to perform functions in altered developmental contexts. A mechanistic understanding of how central neurons change their anatomy to meet new functional requirements will benefit greatly from the establishment of a model preparation where cellular and molecular changes can be examined in an identified central neuron. RESULTS: In this study, we examine a wide-field serotonergic neuron in the Drosophila olfactory pathway and map the dramatic changes that it undergoes from larva to adult. We show that expression of a dominant-negative form of the ecdysterone receptor prevents remodeling. We further use different transgenic constructs to silence neuronal activity and report defects in the morphology of the adult-specific dendritic trees. The branching of the presynaptic axonal arbors is regulated by mechanisms that affect axon growth and retrograde transport. The neuron develops its normal morphology in the absence of sensory input to the antennal lobe, or of the mushroom bodies. However, ablation of its presumptive postsynaptic partners, the projection neurons and/or local interneurons, affects the growth and branching of terminal arbors. CONCLUSION: Our studies establish a cellular system for studying remodeling of a central neuromodulatory feedback neuron and also identify key elements in this process. Understanding the morphogenesis of such neurons, which have been shown in other systems to modulate the sensitivity and directionality of response to odors, links anatomy to the development of olfactory behavior.RIGHTS : This article is licensed under the BioMed Central licence at http://www.biomedcentral.com/about/license which is similar to the 'Creative Commons Attribution Licence'. In brief you may : copy, distribute, and display the work; make derivative works; or make commercial use of the work - under the following conditions: the original author must be given credit; for any reuse or distribution, it must be made clear to others what the license terms of this work are

Shaping leg muscles in Drosophila: role of ladybird, a conserved regulator of appendicular myogenesis

Legs are locomotor appendages used by a variety of evolutionarily distant vertebrates and invertebrates. The primary biological leg function, locomotion, requires the formation of a specialised appendicular musculature. Here we report evidence that ladybird, an orthologue of the Lbx1 gene recognised as a hallmark of appendicular myogenesis in vertebrates, is expressed in leg myoblasts, and regulates the shape, ultrastructure and functional properties of leg muscles in Drosophila. ladybird expression is progressively activated in myoblasts associated with the imaginal leg disc and precedes that of the founder cell marker dumbfounded. The RNAi-mediated attenuation of ladybird expression alters properties of developing myotubes, impairing their ability to grow and interact with the internal tendons and epithelial attachment sites. It also affects sarcomeric ultrastructure, resulting in reduced leg muscle performance and impaired mobility in surviving flies. The over-expression of ladybird also results in an abnormal pattern of dorsally located leg muscles, indicating different requirements for ladybird in dorsal versus ventral muscles. This differential effect is consistent with the higher level of Ladybird in ventrally located myoblasts and with positive ladybird regulation by extrinsic Wingless signalling from the ventral epithelium. In addition, ladybird expression correlates with that of FGF receptor Heartless and the read-out of FGF signalling downstream of FGF. FGF signals regulate the number of leg disc associated myoblasts and are able to accelerate myogenic differentiation by activating ladybird, leading to ectopic muscle fibre formation. A key role for ladybird in leg myogenesis is further supported by its capacity to repress vestigial and to down-regulate the vestigial-governed flight muscle developmental programme. Thus in Drosophila like in vertebrates, appendicular muscles develop from a specialised pool of myoblasts expressing ladybird/Lbx1. The ladybird/Lbx1 gene family appears as a part of an ancient genetic circuitry determining leg-specific properties of myoblasts and making an appendage adapted for locomotion