Generation of MuRF-GFP transgenic zebrafish models for investigating murf gene expression and protein localization in Smyd1b and Hsp90α1 knockdown embryos

Muscle peripheral circadian clock drives nocturnal protein degradation via raised Ror/Rev-erb balance and prevents premature sarcopenia

How central and peripheral circadian clocks regulate protein metabolism and affect tissue mass homeostasis has been unclear. Circadian shifts in the balance between anabolism and catabolism control muscle growth rate in young zebrafish independent of behavioral cycles. Here, we show that the ubiquitin-proteasome system (UPS) and autophagy, which mediate muscle protein degradation, are each upregulated at night under the control of the muscle peripheral clock. Perturbation of the muscle transcriptional molecular clock disrupts nocturnal proteolysis, increases muscle growth measured over 12 h, and compromises muscle function. Mechanistically, the shifting circadian balance of Ror and Rev-erb regulates nocturnal UPS, autophagy, and muscle growth through altered TORC1 activity. Although environmental zeitgebers initially mitigate defects, lifelong muscle clock inhibition reduces muscle size and growth rate, accelerating aging-related loss of muscle mass and function. Circadian misalignment such as shift work, sleep deprivation, or dementia may thus unsettle muscle proteostasis, contributing to muscle wasting and sarcopenia.

Integrated cellular response of the zebrafish (Danio rerio) heart to temperature change

A decrease in environmental temperature represents a challenge to the cardiovascular system of ectotherms. To gain insight into the cellular changes that occur during cold exposure and cold acclimation we characterized the cardiac phosphoproteome and proteome of zebrafish following 24 h or 1 week exposure to 20°C from 27°C; or at multiple points during 6 weeks of acclimation to 20°C from 27°C. Our results indicate that cold exposure causes an increase in mitogen-activated protein kinase signalling, the activation of stretch-sensitive pathways, cellular remodelling via ubiquitin-dependent pathways and changes to the phosphorylation state of proteins that regulate myofilament structure and function including desmin and troponin T. Cold acclimation (2-6 weeks) led to a decrease in multiple components of the electron transport chain through time, but an increase in proteins for lipid transport, lipid metabolism, the incorporation of polyunsaturated fatty acids into membranes and protein turnover. For example, there was an increase in the levels of apolipoprotein C, prostaglandin reductase-3 and surfeit locus protein 4, involved in lipid transport, lipid metabolism and lipid membrane remodelling. Gill opercular movements suggest that oxygen utilization during cold acclimation is reduced. Neither the amount of food consumed relative to body mass nor body condition was affected by acclimation. These results suggest that while oxygen uptake was reduced, energy homeostasis was maintained. This study highlights that the response of zebrafish to a decrease in temperature is dynamic through time and that investment in the proteomic response increases with the duration of exposure.

Molecular chaperone Hsp90 protects KCBP from degradation by proteasome in Dunaliella salina cells

Kinesin-like calmodulin-binding protein (KCBP) is a unique kinesin with half kinesin and half myosin, with kinesin motor domain at C-terminus and myosin tail homology region 4 (MyTH4) and band 4.1, ezrin, radixin, moesin (FERM) domains at N-terminus. The special structure endows KCBP multi-intracellular functions, including cell division, trichome morphogenesis in plants, and flagellar function in algae. However, little is known about the molecular mechanism underlying these functions. Here, we identified a molecular chaperone Hsp90 as a novel binding partner with KCBP in Dunaliella salina using a yeast two-hybrid screen. Further analysis showed that Hsp90 interacted with both the N-terminal and C-terminal of DsKCBP. Since Hsp90 was involved in the stability and proteolytic turnover of numerous proteins, whether Hsp90 regulated the degradation of DsKCBP was investigated. Our results showed that both Hsp90 and DsKCBP presented in the purified proteasome, and the interaction of DsKCBP-Hsp90 was inhibited upon Hsp90 inhibitor geldanamycin treatment. The level of DsKCBP proteins was diminished remarkably indicating that the disassociation of DsKCBP from Hsp90 accelerated the degradation of the former. Furthermore, immunofluorescence results showed that the localization of DsKCBP at basal body and flagella was disappeared by Hsp90 inhibition. The increased mRNA level of DsKCBP during flagellar assembly was not obvious by geldanamycin treatment. These data provided evidence that Hsp90 protected DsKCBP from degradation by proteasome and was involved in the role of DsKCBP in flagellar assembly.

Cloning, characterization, and transcriptional activity of β-actin promoter of African catfish (Clarias gariepinus)

Selection of suitable promoters is crucial for the efficient expression of exogenous genes in transgenic animals. Although one of the most effective promoters, the β-actin promoter, has been widely studied in fish species, it still remains unknown in the economical important African catfish (Clarias gariepinus). In this study, the β-actin promoter of African catfish (cgβ-actinP) was cloned and characterized. In addition, recombinant plasmid pcgβ-actinP-EGFP with enhanced green fluorescent protein (GFP) gene as the reporter gene was constructed to verify the transcriptional activity. We obtained a cgβ-actinP fragment length of 1405 bp, consisting 104 bp of the 5' proximal promoter, 96 bp of the first exon, and 1205 bp of the first intron. Similar to those of other fish species, cgβ-actinP contains three key transcription regulatory elements (CAAT box, CArG motif, and TATA box). GFP-specific fluorescent signals were detected in chicken embryonic fibroblasts cells (DF-1 cells) transfected with pcgβ-actinP-EGFP, which was approximately 1.11 times of the positive control. In addition, GFP was effectively expressed in zebrafish larvae microinjected with linearized cgβ-actinP-EGFP, with expression rate reaching approximately 49.84%. Our data indicate that cgβ-actinP could be a potential candidate promoter in the practice of constructing "all fish" transgenic fish.

Circadian regulation of muscle growth independent of locomotor activity

A long-standing question, particularly in physiotherapy and sports medicine, is whether time of day affects muscle metabolism and hence growth, either intrinsically or in response to exercise or nutrition. Answers would help to identify the best time of day to exercise, build muscle, and prevent aging- or disease-related sarcopenia. Here, we address this question in live zebrafish myotome in vivo, without interference from other circadian oscillations such as locomotor activity and food intake. We show that active muscle anabolizes more in the day and grows faster, while catabolizing more at night and growing slower. Such day/night differences remain in inactive muscle but disappear after clock disruption. We conclude that muscles display circadian differences in growth independent of activity and feeding.

Muscle tissue shows diurnal variations in function, physiology, and metabolism. Whether such variations are dependent on the circadian clock per se or are secondary to circadian differences in physical activity and feeding pattern is unclear. By measuring muscle growth over 12-h periods in live prefeeding larval zebrafish, we show that muscle grows more during day than night. Expression of dominant negative CLOCK (ΔCLK), which inhibits molecular clock function, ablates circadian differences and reduces muscle growth. Inhibition of muscle contraction reduces growth in both day and night, but does not ablate the day/night difference. The circadian clock and physical activity are both required to promote higher muscle protein synthesis during the day compared to night, whereas markers of protein degradation, murf messenger RNAs, are higher at night. Proteasomal inhibitors increase muscle growth at night, irrespective of physical activity, but have no effect during the day. Although physical activity enhances TORC1 activity, and the TORC1 inhibitor rapamycin inhibits clock-driven daytime growth, no effect on muscle growth at night was detected. Importantly, day/night differences in 1) muscle growth, 2) protein synthesis, and 3) murf expression all persist in entrained larvae under free-running constant conditions, indicating circadian drive. Removal of circadian input by exposure to either permanent darkness or light leads to suboptimal muscle growth. We conclude that diurnal variations in muscle growth and metabolism are a circadian property that is independent of, but augmented by, physical activity, at least during development.