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

Autoantibodies neutralizing type I IFNs are present in ~4% of uninfected individuals over 70 years old and account for ~20% of COVID-19 deaths

Publisher Copyright: © 2021 The Authors, some rights reserved.Circulating autoantibodies (auto-Abs) neutralizing high concentrations (10 ng/ml; in plasma diluted 1:10) of IFN-alpha and/or IFN-omega are found in about 10% of patients with critical COVID-19 (coronavirus disease 2019) pneumonia but not in individuals with asymptomatic infections. We detect auto-Abs neutralizing 100-fold lower, more physiological, concentrations of IFN-alpha and/or IFN-omega (100 pg/ml; in 1:10 dilutions of plasma) in 13.6% of 3595 patients with critical COVID-19, including 21% of 374 patients >80 years, and 6.5% of 522 patients with severe COVID-19. These antibodies are also detected in 18% of the 1124 deceased patients (aged 20 days to 99 years; mean: 70 years). Moreover, another 1.3% of patients with critical COVID-19 and 0.9% of the deceased patients have auto-Abs neutralizing high concentrations of IFN-beta. We also show, in a sample of 34,159 uninfected individuals from the general population, that auto-Abs neutralizing high concentrations of IFN-alpha and/or IFN-omega are present in 0.18% of individuals between 18 and 69 years, 1.1% between 70 and 79 years, and 3.4% >80 years. Moreover, the proportion of individuals carrying auto-Abs neutralizing lower concentrations is greater in a subsample of 10,778 uninfected individuals: 1% of individuals 80 years. By contrast, auto-Abs neutralizing IFN-beta do not become more frequent with age. Auto-Abs neutralizing type I IFNs predate SARS-CoV-2 infection and sharply increase in prevalence after the age of 70 years. They account for about 20% of both critical COVID-19 cases in the over 80s and total fatal COVID-19 cases.Peer reviewe

The conserved transcription factor Mef2 has multiple roles in adult Drosophila musculature formation

Muscle is an established paradigm for analysing the cell differentiation programs that underpin the production of specialised tissues during development. These programs are controlled by key transcription factors, and a well-studied regulator of muscle gene expression is the conserved transcription factor Mef2. In vivo, Mef2 is essential for the development of the Drosophila larval musculature: Mef2-null embryos have no differentiated somatic muscle. By contrast, a similar phenotype has not been seen in analyses of the function of Mef2 genes in other examples of myogenesis. These include using conditional mutant mice, using morpholinos in zebrafish and using hypomorphic mutants in Drosophila adult development. However, we show here that Mef2 is absolutely required for a diverse range of Drosophila adult muscle types. These include the dorso-longitudinal muscles (DLMs), the largest flight muscles, which are produced by tissue remodelling. Furthermore, we demonstrate that Mef2 has temporally separable functions in this remodelling and in muscle maintenance. Drosophila adult muscles are multi-fibre and physiologically diverse, in common with vertebrate skeletal muscles, but in contrast to Drosophila larval muscles. These results therefore establish the importance of Mef2 in multiple roles in examples of myogenesis that have parallels in vertebrates and are distinct from that occurring in Drosophila embryogenesis

Critical aspects in the production of periodically ordered mesoporous titania thin films

International audiencePeriodically ordered mesoporous titania thin films (MTTF) present a high surface area, controlled porosity in the 2–20 nm pore diameter range and an amorphous or crystalline inorganic framework. These materials are nowadays routinely prepared by combining soft chemistry and supramolecular templating. Photocatalytic transparent coatings and titania-based solar cells are the immediate promising applications. However, a wealth of new prospective uses have emerged on the horizon, such as advanced catalysts, perm-selective membranes, optical materials based on plasmonics and photonics, metamaterials, biomaterials or new magnetic nanocomposites. Current and novel applications rely on the ultimate control of the materials features such as pore size and geometry, surface functionality and wall structure. Even if a certain control of these characteristics has been provided by the methods reported so far, the needs for the next generation of MTTF require a deeper insight in the physical and chemical processes taking place in their preparation and processing. This article presents a critical discussion of these aspects. This discussion is essential to evolve from know-how to sound knowledge, aiming at a rational materials design of these fascinating systems

<i>lb</i> is required for proper leg muscle performance and walking behaviour

<p>A The ball test see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0000122#pone.0000122.s012" target="_blank">Videos S10</a>–<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0000122#pone.0000122.s014" target="_blank">S12</a>. The abilities of flies to catch, maintain and rotate a polystyrene ball were tested. The number of individuals tested males only is indicated in upper case after the genotype. Each male performed each of the tests three times. The number of asterisks max. 5 illustrates the average performance. Notice that the RNAi-based attenuation of <i>lb</i> leads to a reduced ability to catch about 20% of failures and especially to maintain the ball about 60% of failures with slower and irregular rotations. Defects in catching, maintaining and rotating the ball were comparatively stronger in flies overexpressing <i>lb</i>. About 60% of flies were unable to catch the ball and more than 80% lost it in less than 30 s. B The ‘leg-print’ test for walking pattern. Two-day old flies were allowed to walk on a carbon-soot coated glass slide and their tracks were examined. The direction of movement is towards the top of each panel. The imprints made by the first 1 second 2 and third leg 3 of the left hemisegment are marked in each panel. Wild type flies B′ show a stereotypic pattern of prints, a consequence of a ‘tripod’ gait. In male flies where UAS-lbRNAi expression is under the control of the 1151GAL4 driver B″ the legs are held closer to the body and the leg-print is the consequence of a shuffling gait. In male flies where UAS-lbe expression is under the control of the 1151GAL4 driver the pattern of prints B′″ illustrates a bias towards one side, a consequence of the legs being abnormally positioned with respect to the body.</p

Lbe is dynamically expressed in leg disc myoblasts.

<p>A–F Confocal images of leg imaginal discs stained with anti-Twi A, D and blue in merge C, F, and anti-Lbe B, E and green in merge C, F antibodies. A–C Third instar leg imaginal disc. B Lbe expression can be seen in subsets of Twi myoblasts, associated with regions of the leg disc that develop into different segments of the adult leg. Arrows in B, E show a group of myoblasts that give rise to dorsal femur muscle, tilm. The arrowheads in B, E point to precursors of ventral femur muscle, tidm. D–F″ 0 hr APF leg imaginal disc. Myoblasts are regionalised at this stage and are seen at future muscle-forming sites in adult tibia tadm, talm, femur tidm, tilm, trocanter Tr, coxa Co. Lbe is expressed in almost all Twist myoblast subsets at specific sites along the proximal-distal axis in the leg disc proper. Most proximal cells including the dorsal proximal myoblasts asterisks in C, F are devoid of Lbe expression. F′, F″ Two different views of a 3D reconstruction see also <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0000122#pone.0000122.s003" target="_blank">Video 1S</a> of the disc presented in F showing spatial distribution of different groups of leg myoblasts. G The schematic of F showing positions of Lbe-positive myoblasts within the leg segments. Lbe is also expressed in leg disc epithelium in the ventral region black asterisks in B, E and the long tendon yellow arrow in E. Abbreviations: Ta, tarsus, Ti, tibia, Fe, femur, see also 22 for muscle nomenclature.</p

Wg signals are required for Lbe expression and play a key role in leg myogenesis

<p>A–I Confocal images of third instar leg imaginal discs. A–C Wild type leg disc stained for Lbe and Vestigial Vg. Lbe positive myoblasts are seen in leg disc proper B and green in merge C, while the myoblasts associated with the dorsal proximal region corresponding to the ventral thorax express Vg A and red in merge C. Vg myoblasts are devoid of Lbe asterisk in B. A Yellow arrowhead shows myoblasts expressing high levels of Vg and white arrowhead those expressing Vg at lower levels. D–F Leg disc, in which a dominant-negative TCF has been expressed in the myoblasts. Myoblasts are present as shown by anti-Twist antibody staining D and blue in merge F, but Lbe expression in myoblasts is lost asterisks in E and green in F. G–I Leg disc, in which activated Armadillo Arm transgene has been expressed in the myoblasts. Lbe is ectopically expressed in dorsal proximal myoblasts arrow in H and green in merge I, normally devoid of Lbe. Myoblasts are visualised with anti-Twi antibody G and blue in I. J–J′ show adult muscle phenotypes in the femur region induced by 1151-Gal4-driven forced expression of a dominant-negative TCF. Ventral muscles tidm are partially lost asterisks in J or completely lost asterisks in J′ and dorsal muscles tilm are severely affected. Muscles are visualised using MHC-tauGFP. Anterior views from the 3D reconstructions of confocal scans. K A schematic showing position of Lbe-expressing dorsal tilm and ventral tidm precursors of femur muscles green areas with respect to epithelial Wg expression domain violet triangle. The dorsal tilm myoblasts, located comparatively far from the Wg domain, receive a lower level of Wg morphogen long thin arrow than ventrally located tidm myoblasts short thick arrow.</p