Regulation of fiber-specific actin expression by the Drosophila SRF ortholog Blistered

The divergent intron-containing actin in sponge morphogenetic processes

The ability of eukaryotic cells to orchestrate mechanical interactions from the subcellular to the organismal levels is mediated by their cytoskeleton. One of the key components of the eukaryotic cytoskeleton is actin, a highly conserved building block of the actin filaments, which interact with many other proteins and underlie diverse cell structures, necessary for organizing intracellular transport, phagocytosis and cell movement. Many organisms have evolved multiple actin variants, which share similar amino acid sequences but differ more dramatically at the gene level, including the presence and number of introns. In the current study, we show that the intron-containing and intronless actin genes are present in the poriferan Halisarca dujardini and that the encoded actins can perform different functions. These actins differ in the gene expression profiles, post-translational modifications, cellular, and subcellular localizations. The intronless actin genes of H. dujardini, HdA1/2/3, are products of recent duplications, exhibit low divergence between paralogs, and serve as the primary cytoskeletal actins. The divergent intron-containing actin gene, HdA6, is differentially expressed in a specific cell lineage and its expression is dependent on the state of cell aggregation, which indicates its unique functions in the morphogenetic processes of the sponge.

Neuronal innervation regulates the secretion of neurotrophic myokines and exosomes from skeletal muscle

Myokines and exosomes, originating from skeletal muscle, are shown to play a significant role in maintaining brain homeostasis. While exercise has been reported to promote muscle secretion, little is known about the effects of neuronal innervation and activity on the yield and molecular composition of biologically active molecules from muscle. As neuromuscular diseases and disabilities associated with denervation impact muscle metabolism, we hypothesize that neuronal innervation and firing may play a pivotal role in regulating secretion activities of skeletal muscles. We examined this hypothesis using an engineered neuromuscular tissue model consisting of skeletal muscles innervated by motor neurons. The innervated muscles displayed elevated expression of mRNAs encoding neurotrophic myokines, such as interleukin-6, brain-derived neurotrophic factor, and FDNC5, as well as the mRNA of peroxisome-proliferator-activated receptor γ coactivator 1α, a key regulator of muscle metabolism. Upon glutamate stimulation, the innervated muscles secreted higher levels of irisin and exosomes containing more diverse neurotrophic microRNAs than neuron-free muscles. Consequently, biological factors secreted by innervated muscles enhanced branching, axonal transport, and, ultimately, spontaneous network activities of primary hippocampal neurons in vitro. Overall, these results reveal the importance of neuronal innervation in modulating muscle-derived factors that promote neuronal function and suggest that the engineered neuromuscular tissue model holds significant promise as a platform for producing neurotrophic molecules.

Atypical laminin spots and pull-generated microtubule-actin projections mediate Drosophila wing adhesion

During Drosophila metamorphosis, dorsal and ventral wing surfaces adhere, separate, and reappose in a paradoxical process involving cell-matrix adhesion, matrix production and degradation, and long cellular projections. The identity of the intervening matrix, the logic behind the adhesion-reapposition cycle, and the role of projections are unknown. We find that laminin matrix spots devoid of other main basement membrane components mediate wing adhesion. Through live imaging, we show that long microtubule-actin cables grow from those adhesion spots because of hydrostatic pressure that pushes wing surfaces apart. Formation of cables resistant to pressure requires spectraplakin, Patronin, septins, and Sdb, a SAXO1/2 microtubule stabilizer expressed under control of wing intervein-selector SRF. Silkworms and dead-leaf butterflies display similar dorso-ventral projections and expression of Sdb in intervein SRF-like patterns. Our study supports the morphogenetic importance of atypical basement-membrane-related matrices and dissects matrix-cytoskeleton coordination in a process of great evolutionary significance.

Analysis of Differentially Expressed Genes of Chrysoperla sinica Related to Flight Capacity by Transcriptome

The lacewing Chrysoperla sinica (Tjeder) is a common natural enemy of many insect pests in China and is frequently employed for biological control programs. Adults make migratory flights after emergence, which reduces their effectiveness as biological control agents. Previously, we proved that 2-d-old unmated females exhibited significantly stronger flight ability than 3-d-old ones. Meanwhile, 3-d-old unmated adults flew significantly longer distances than mated ones. In this study, Illumina RNA sequencing was performed to characterize differentially expressed genes (DEGs) between virgin and mated adults of different ages in a single female strain of C. sinica. In total, 713,563,726 clean reads were obtained and de novo assembled into 109,165 unigenes with an average length of 847 bp (N50 of 1,754 bp), among which 4,382 (4.01%) unigenes matched known proteins. Based on these annotations, many putative transcripts were related to C. sinica's flight capacity and muscle structure, energy supply, growth, development, environmental adaptability, and metabolism of nutritional components and bioactive components. In addition, the differential expression of transcripts between different ages and mating status were analyzed, and DEGs participating in flight capacity and muscles were detected, including glutathione hydrolase, NAD-specific glutamate dehydrogenase, aminopeptidase, and acidic amino acid decarboxylase. The DEGs with functions associated with flight capacity and muscles exhibited higher transcript levels for younger (2 d--old) virgins. This comprehensive C. sinica transcriptomic data provide a foundation for a better understanding of the molecular mechanisms underlying the flight capacity to meet the physiological demands of flight muscles in C. sinica.

Genetic Control of Muscle Diversification and Homeostasis: Insights from Drosophila

In the fruit fly, Drosophila melanogaster, the larval somatic muscles or the adult thoracic flight and leg muscles are the major voluntary locomotory organs. They share several developmental and structural similarities with vertebrate skeletal muscles. To ensure appropriate activity levels for their functions such as hatching in the embryo, crawling in the larva, and jumping and flying in adult flies all muscle components need to be maintained in a functionally stable or homeostatic state despite constant strain. This requires that the muscles develop in a coordinated manner with appropriate connections to other cell types they communicate with. Various signaling pathways as well as extrinsic and intrinsic factors are known to play a role during Drosophila muscle development, diversification, and homeostasis. In this review, we discuss genetic control mechanisms of muscle contraction, development, and homeostasis with particular emphasis on the contractile unit of the muscle, the sarcomere.

Contributions of alternative splicing to muscle type development and function

Animals possess a wide variety of muscle types that support different kinds of movements. Different muscles have distinct locations, morphologies and contractile properties, raising the question of how muscle diversity is generated during development. Normal aging processes and muscle disorders differentially affect particular muscle types, thus understanding how muscles normally develop and are maintained provides insight into alterations in disease and senescence. As muscle structure and basic developmental mechanisms are highly conserved, many important insights into disease mechanisms in humans as well as into basic principles of muscle development have come from model organisms such as Drosophila, zebrafish and mouse. While transcriptional regulation has been characterized to play an important role in myogenesis, there is a growing recognition of the contributions of alternative splicing to myogenesis and the refinement of muscle function. Here we review our current understanding of muscle type specific alternative splicing, using examples of isoforms with distinct functions from both vertebrates and Drosophila. Future exploration of the vast potential of alternative splicing to fine-tune muscle development and function will likely uncover novel mechanisms of isoform-specific regulation and a more holistic understanding of muscle development, disease and aging.