Independent pathways control muscle tissue size and sarcomere remodeling.

Cell growth and proliferation must be balanced during development to attain a final adult size with the appropriate proportions of internal organs to maximize fitness and reproduction. While multiple signaling pathways coordinate Drosophila development, it is unclear how multi-organ communication within and between tissues converge to regulate systemic growth. One such growth pathway, mediated by insulin-like peptides that bind to and activate the insulin receptor in multiple target tissues, is a primary mediator of organismal size. Here we uncover a signaling role for the NUAK serine/threonine kinase in muscle tissue that impinges upon insulin pathway activity to limit overall body size, including a reduction in the growth of individual organs. In skeletal muscle tissue, manipulation of NUAK or insulin pathway components influences sarcomere number concomitant with modulation of thin and thick filament lengths, possibly by modulating the localization of Lasp, a nebulin repeat protein known to set thin filament length. This mode of sarcomere remodeling does not occur in other mutants that also exhibit smaller muscles, suggesting that a sensing mechanism exists in muscle tissue to regulate sarcomere growth that is independent of tissue size control.

Protocol for affinity purification-mass spectrometry interactome profiling in larvae of Drosophila melanogaster.

Many techniques exist for the identification of protein interaction networks. We present a protocol that relies on an affinity purification-mass spectrometry (AP-MS) approach to detect proteins that co-purify with a tagged bait of interest from Drosophila melanogaster larval muscles using the GAL4/upstream activating sequence (UAS) expression system. We also describe steps for the isolation and identification of protein complexes, followed by streamlined bioinformatics analysis for rapid and reproducible results. This protocol can be extended to investigate protein interactions in other tissues. For complete details on the use and execution of this protocol, please refer to Guo et al.1.

Orchestration of autophagosome fusion by STRIPAK complex components in muscle tissue.

Autophagy is a central process responsible for the disposal of normal as well as damaged cellular proteins and organelles. Proper regulation of multiple steps - including initiation and the fusion between autophagosomes and lysosomes - is essential for the completion of cargo disposal. While the function of many proteins that mediate canonical autophagy has been characterized, the identification of new autophagy regulators may shed light on differences between tissues and/or responses to cellular stresses. In this punctum, we discuss our recent findings about how the Striatin-Interacting Phosphatase and Kinase (STRIPAK)-NUAK-Starvin (Stv) complex coordinately regulates autophagy in the muscle tissue of Drosophila melanogaster.

Identification of CryAB as a target of NUAK kinase activity in Drosophila muscle tissue.

Phosphorylation reactions performed by protein kinases are one of the most studied post-translational modifications within cells. Much is understood about conserved residues within protein kinase domains that perform catalysis of the phosphotransfer reaction, yet the identity of the target substrates and downstream biological effects vary widely among cells, tissues, and organisms. Here, we characterize key residues essential for NUAK kinase activity in Drosophila melanogaster myogenesis and homeostasis. Creation of a NUAK kinase-dead mutation using Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR)/Cas9 results in lethality at the embryo to larval transition, while loss of NUAK catalytic function later in development produces aggregation of the chaperone protein αB-crystallin/CryAB in muscle tissue. Yeast 2-hybrid assays demonstrate a physical interaction between NUAK and CryAB. We further show that a phospho-mimetic version of NUAK promotes the phosphorylation of CryAB and this post-translational modification occurs at 2 previously unidentified phosphosites that are conserved in the primary sequence of human CryAB. Mutation of these serine residues in D. melanogaster NUAK abolishes CryAB phosphorylation, thus, proving their necessity at the biochemical level. These studies together highlight the importance of kinase activity regulation and provide a platform to further explore muscle tissue proteostasis.

A conserved STRIPAK complex is required for autophagy in muscle tissue.

Autophagy is important for cellular homeostasis and to prevent the abnormal accumulation of proteins. While many proteins that comprise the canonical autophagy pathway have been characterized, the identification of new regulators may help understand tissue and/or stress-specific responses. Using an in-silico approach, we identified Striatin interacting protein (Strip), MOB kinase activator 4, and fibroblast growth factor receptor 1 oncogene partner 2 as conserved mediators of muscle tissue maintenance. We performed affinity purification-mass spectrometry (AP-MS) experiments with Drosophila melanogaster Strip as a bait protein and copurified additional Striatin-interacting phosphatase and kinase (STRIPAK) complex members from larval muscle tissue. NUAK family kinase 1 (NUAK) and Starvin (Stv) also emerged as Strip-binding proteins and these physical interactions were verified in vivo using proximity ligation assays. To understand the functional significance of the STRIPAK-NUAK-Stv complex, we employed a sensitized genetic assay combined with RNA interference (RNAi) to demonstrate that both NUAK and stv function in the same biological process with genes that encode for STRIPAK complex proteins. RNAi-directed knockdown of Strip in muscle tissue led to the accumulation of ubiquitinated cargo, p62, and Autophagy-related 8a, consistent with a block in autophagy. Indeed, autophagic flux was decreased in Strip RNAi muscles, while lysosome biogenesis and activity were unaffected. Our results support a model whereby the STRIPAK-NUAK-Stv complex coordinately regulates autophagy in muscle tissue.

How Does Organizational Compassion Motivate Employee Innovative Behavior: A Cross-Level Mediation Model.

This study aims to explore the mediating mechanisms between organizational compassion and employee innovative behavior by introducing perceived insider status and felt responsibility for constructive change (FRCC) as mediating variables. Drawing on cognitive-affective personality system theory, a cross-level mediation model was established. Data were collected via the online-based questionnaire from 420 employees of 12 enterprises in China. Multilevel path modeling was leveraged to examine hypotheses proposed in this study. The results indicate that FRCC mediates the relationship between organizational compassion and employee innovative behavior. Moreover, perceived insider status and FRCC serially mediate the relationship between organizational compassion and employee innovative behavior. This study has significant theoretical and practical implications as it is the first study to investigate the value of organizational compassion to employee innovative behavior at the workplace.

How Does Transformational Leadership Relieve Teacher Burnout: The Role of Self-Efficacy and Emotional Intelligence.

This study explored the underlying mechanisms and boundary conditions of the relationship between transformational leadership and teacher burnout. Specifically, it investigated the mediating role of teacher self-efficacy and the moderating role of teacher emotional intelligence (EI) in this relationship. Data from 539 primary and secondary school teachers were analyzed using Structural Equation Model and hierarchical regression. The results indicate that transformational leadership predicted teacher burnout negatively, self-efficacy mediated the association of transformational leadership with burnout partially, and EI strengthened the association between transformational leadership and burnout. This study has important theoretical and managerial implications as it deepens the understanding of the association between transformational leadership and burnout in the educational field and provides practical suggestions on how to relieve teacher burnout in the school context.

Give a Man a Fish or Teach a Man to Fish: A Cross-Level Moderated Mediation Model of Cognitive and Performance Responses of Team Members to Help of Team Leaders.

Drawing upon theoretical lenses of social cognitive theory, this study explores whether, when, why, and how the helping behaviors of team leaders influence individual work role performance of team members (in terms of individual task proficiency, task adaptivity, and task proactivity) through self-efficacy of team members. The consequences of different types of help of leaders are uncovered in this study. By proposing a cross-level moderated mediation model and using multisource and multistage data from 303 team members in 39 work teams, autonomy-oriented help of leaders was found to have a differential effect on individual work role performance of members via the self-efficacy of the latter when controlling for dependency-oriented help of leaders. Moreover, the multilevel analysis of moderation uncovered that leader-member exchange relationship at the team level engendered a boundary condition for the mediating role of member self-efficacy in the relationship between autonomy-oriented help of leaders and individual work role performance of members in this model.

Are Empowered Employees More Proactive? The Contingency of How They Evaluate Their Leader.

Finding ways to enhance employee proactive behavior is a focal concern for academics and practitioners. Previous studies have found a positive association between empowering leadership and proactive behavior (Martin et al., 2013; Li et al., 2017). However, these studies lack elaboration on mechanisms and do not rule out the effect of employees' proactive personality during empirical testing. We investigate empowering leadership from individual perspective due to the variation of empowerment levels even in the same team. Our research proposes a more elaborated theoretical model that explains why, and when, empowering leadership might promote employee proactive behavior. Specifically, we examine mediating mechanisms based on social cognitive theory and propose trust in leader competency as boundary condition. Using a sample of 280 leader-follower dyads from a large state-owned Chinese company, our results revealed that (1) empowering leadership was positively related to proactive behavior, with role breadth self-efficacy acting as a mediator for this relationship; (2) employees' trust in leader competency moderated both the empowering leadership-subordinate proactive behavior relationship and the mediating effect of role breadth self-efficacy, such that the empowering leadership-subordinate proactive behavior relationship was weaker, and the mediating effect of role breadth self-efficacy was stronger, for employees with high levels of trust in leader competency.