CKIP-1 regulates mammalian and zebrafish myoblast fusion

Genomic Scan for Runs of Homozygosity and Selective Signature Analysis to Identify Candidate Genes in Large White Pigs

Large White pigs are extensively utilized in China for their remarkable characteristics of rapid growth and the high proportion of lean meat. The economic traits of pigs, comprising reproductive and meat quality traits, play a vital role in swine production. In this study, 2295 individuals, representing three different genetic backgrounds Large White pig populations were used: 500 from the Canadian line, 295 from the Danish line, and 1500 from the American line. The GeneSeek 50K GGP porcine HD array was employed to genotype the three pig populations. Firstly, genomic selective signature regions were identified using the pairwise fixation index (FST) and locus-specific branch length (LSBL). By applying a top 1% threshold for both parameters, a total of 888 candidate selective windows were identified, harbouring 1571 genes. Secondly, the investigation of regions of homozygosity (ROH) was performed utilizing the PLINK software. In total, 25 genomic regions exhibiting a high frequency of ROHs were detected, leading to the identification of 1216 genes. Finally, the identified potential functional genes from candidate genomic regions were annotated, and several important candidate genes associated with reproductive traits (ADCYAP1, U2, U6, CETN1, Thoc1, Usp14, GREB1L, FGF12) and meat quality traits (MiR-133, PLEKHO1, LPIN2, SHANK2, FLVCR1, MYL4, SFRP1, miR-486, MYH3, STYX) were identified. The findings of this study provide valuable insights into the genetic basis of economic traits in Large White pigs and may have potential use in future pig breeding programs.

CKIP-1 mediates P. gingivalis-suppressed osteogenic/cementogenic differentiation of periodontal ligament cells partially via p38 signaling pathway

Objectives

Casein kinase 2 interacting protein-1 (CKIP-1) is a versatile player involved in various biological processes. However, whether CKIP-1 mediates the osteogenic/cementogenic differentiation of periodontal ligament cells (PDLCs) under Porphyromonas gingivalis (Pg) stimulation remains unknown.

Material and Methods

The effect of Pg on PDLC differentiation was first verified. CKIP-1 expression in Pg-infected PDLCs or in PDL of apical periodontitis (AP) mice was detected. The changes of CKIP-1 during PDLC differentiation was also determined. PDLC differentiation capacity in CKIP-1 knockout (KO) mice and CKIP-1-silenced PDLCs with or without Pg stimulation were further studied. Inhibitor was finally applied to verify the involvement of p38 signaling pathway in PDLC differentiation.

Results

The suppression effect of Pg on PDLC differentiation was demonstrated. CKIP-1 increased in the PDL of AP mice and Pg-induced PDLCs, and decreased gradually during PDLC differentiation. Increased OSX and RUNX2 expression in PDL were observed in CKIP-1 KO mice. Also, CKIP-1 silencing facilitated and rescued Pg-inhibited PDLC differentiation. Inhibitor for p38 signaling pathway blocked CKIP-1 silencing-facilitated PDLC differentiation.

Conclusions

CKIP-1 mediated the osteogenic/cementogenic differentiation of PDLCs partially through p38 signaling pathway, which may provide evidence for the regeneration of periodontal hard tissues damaged by Pg.

Casein kinase 2 interacting protein 1 positively regulates caudal-related homeobox 1 in intestinal-type gastric cancer

BACKGROUND

Gastric cancer (GC) is one of the most common malignancies, and intestinal-type GC is the main histopathologic type of GC in China. We previously reported that casein kinase 2 interacting protein 1 (CKIP-1) acts as a candidate tumor suppressor in intestinal-type GC. CKIP-1 participates in the regulation of multiple signaling pathways, including the Wnt/β-catenin pathway, of which caudal-related homeobox 1 (CDX1) may be a downstream target gene. The purpose of this study was to investigate the relationship between CKIP-1 and CDX1 in intestinal-type GC.

METHODS

Sixty-seven gastroscopy biopsy specimens and surgically resected gastric specimens were divided into four groups: gastric mucosa group, intestinal metaplasia (IM) group, dysplasia group, and intestinal-type GC group. The expression levels of CKIP-1 and CDX1 were detected in these groups and GC cell lines, and the correlations between these expression levels were analyzed. SGC7901 and BGC823 cells were divided into CKIP-1 shRNA groups and CKIP-1 over-expression groups, and CDX1 expression was detected. β-Catenin expression was detected in intestinal-type GC tissue samples and CKIP-1 shRNA and CKIP-1 over-expression SGC7901 cells, and its correlation with CKIP-1 expression in intestinal-type GC tissue was analyzed. The Wnt/β-catenin pathway inhibitor DKK-1 and activator LiCl were incubated with SGC7901 cells, BGC823 cells, and CKIP-1 shRNA and CKIP-1 over-expression SGC7901 and BGC823 cells, following which CDX1 and Ki-67 expression were detected.

RESULTS

The expression levels of CKIP-1 and CDX1 were lower in patients with intestinal-type GC than in patients with IM and dysplasia (both P < 0.05). CKIP-1 and CDX1 expression levels were positively correlated in IM, dysplasia, and intestinal-type GC tissue and cell lines (r = 0.771, P < 0.01; r = 0.597, P < 0.01; r = 0.654, P < 0.01; r = 0.811, P < 0.01, respectively). CDX1 expression was decreased in the CKIP-1 shRNA groups and increased in the CKIP-1 over-expression groups of SGC7901 and BGC823 cells compared to that in the corresponding control groups (both P < 0.05). CKIP-1 expression was negatively correlated with β-catenin expression in intestinal-type GC patients (r = -0.458, P < 0.01). Compared to the control group, β-catenin expression was increased in the CKIP-1 shRNA SGC7901 cell group and decreased in the CKIP-1 over-expression SGC7901 cell group (P < 0.05). CDX1 expression was increased in SGC7901 and BGC823 cells treated with DKK-1, DKK-1 increased CDX1 expression and decreased Ki-67 expression in the CKIP-1 shRNA group; the opposite result was observed in SGC7901 and BGC823 cells treated with LiCl, and LiCl decreased CDX1 expression and increased Ki-67 expression in the CKIP-1 over-expression group (both P < 0.05).

CONCLUSIONS

Through the Wnt/β-catenin signaling pathway, CKIP-1 may positively regulate CDX1 in intestinal-type GC.

Proteomic resolution of IGFN1 complexes reveals a functional interaction with the actin nucleating protein COBL

The Igfn1 gene produces multiple proteins by alternative splicing predominantly expressed in skeletal muscle. Igfn1 deficient clones derived from C2C12 myoblasts show reduced fusion index and morphological differences compared to control myotubes. Here, we first show that G:F actin ratios are significantly higher in differentiating IGFN1-deficient C2C12 myoblasts, suggesting that fusion and differentiation defects are underpinned by deficient actin remodelling. We obtained pull-downs from skeletal muscle with IGFN1 fragments and applied a proteomics approach. The proteomic composition of IGFN1 complexes identified the cytoskeleton and an association with the proteasome as the main networks. The actin nucleating protein COBL was selected for further validation. COBL is expressed in C2C12 myoblasts from the first stages of myoblast fusion but not in proliferating cells. COBL is also expressed in adult muscle and, as IGFN1, localizes to the Z-disc. We show that IGFN1 interacts, stabilizes and colocalizes with COBL and prevents the ability of COBL to form actin ruffles in COS7 cells. COBL loss of function C2C12-derived clones are able to fuse, therefore indicating that COBL or the IGFN1/COBL interaction are not essential for myoblast fusion.

Regulation of growth-related genes by nutrition in paralarvae of the common octopus (Octopus vulgaris)

The common octopus (Octopus vulgaris) is a species of great interest to the aquaculture industry. However, the high mortalities registered during different phases of the octopus lifecycle, particularly the paralarvae stage, present a challenge for commercial aquaculture. Improvement of diet formulation is seen as one way to reduce mortality and improve growth. Molecular growth-markers could help to improve rearing protocols and increase survival and growth performance; therefore, over a hundred orthologous genes related to protein balance and muscle growth in vertebrates were identified for the common octopus and their suitability as molecular markers for growth in octopus paralarvae explored. We successfully amplified 14 of those genes and studied their transcription in paralarvae either fed with artemia, artemia + zoea diets or submitted to a short fasting-refeeding procedure. Paralarvae fed with artemia + zoea had higher growth rates compared to those fed only with artemia, as well as a significant increase in octopus mtor (mtor-L) and hsp90 (hsp90-L) transcription, with both genes also up-regulated during refeeding. Our results suggest that at least mtor-L and hsp90-L are likely linked to somatic growth in octopus paralarvae. Conversely, ckip1-L, crk-L, src-L and srf-L had expression patterns that did not match to periods of growth as would be expected based on similar studies in vertebrates, indicating that further research is needed to understand their function during growth and in a muscle specific context.

Cell fusion is differentially regulated in zebrafish post-embryonic slow and fast muscle

Skeletal muscle fusion occurs during development, growth, and regeneration. To investigate how muscle fusion compares among different muscle cell types and developmental stages, we studied muscle cell fusion over time in wild-type, myomaker (mymk), and jam2a mutant zebrafish. Using live imaging, we show that embryonic myoblast elongation and fusion correlate tightly with slow muscle cell migration. In wild-type embryos, only fast muscle fibers are multinucleate, consistent with previous work showing that the cell fusion regulator gene mymk is specifically expressed throughout the embryonic fast muscle domain. However, by 3 weeks post-fertilization, slow muscle fibers also become multinucleate. At this late-larval stage, mymk is not expressed in muscle fibers, but is expressed in small cells near muscle fibers. Although previous work showed that both mymk and jam2a are required for embryonic fast muscle cell fusion, we observe that muscle force and function is almost normal in mymk and jam2a mutant embryos, despite the lack of fast muscle multinucleation. We show that genetic requirements change post-embryonically, with jam2a becoming much less important by late-larval stages and mymk now required for muscle fusion and growth in both fast and slow muscle cell types. Correspondingly, adult mymk mutants perform poorly in sprint and endurance tests compared to wild-type and jam2a mutants. We show that adult mymk mutant muscle contains small mononucleate myofibers with average myonuclear domain size equivalent to that in wild type adults. The mymk mutant fibers have decreased Laminin expression and increased numbers of Pax7-positive cells, suggesting that impaired fiber growth and active regeneration contribute to the muscle phenotype. Our findings identify several aspects of muscle fusion that change with time in slow and fast fibers as zebrafish develop beyond embryonic stages.

The regulatory role of Myomaker and Myomixer-Myomerger-Minion in muscle development and regeneration

Skeletal muscle plays essential roles in motor function, energy, and glucose metabolism. Skeletal muscle formation occurs through a process called myogenesis, in which a crucial step is the fusion of mononucleated myoblasts to form multinucleated myofibers. The myoblast/myocyte fusion is triggered and coordinated in a muscle-specific way that is essential for muscle development and post-natal muscle regeneration. Many molecules and proteins have been found and demonstrated to have the capacity to regulate the fusion of myoblast/myocytes. Interestingly, two newly discovered muscle-specific membrane proteins, Myomaker and Myomixer (also called Myomerger and Minion), have been identified as fusogenic regulators in vertebrates. Both Myomaker and Myomixer-Myomerger-Minion have the capacity to directly control the myogenic fusion process. Here, we review and discuss the latest studies related to these two proteins, including the discovery, structure, expression pattern, functions, and regulation of Myomaker and Myomixer-Myomerger-Minion. We also emphasize and discuss the interaction between Myomaker and Myomixer-Myomerger-Minion, as well as their cooperative regulatory roles in cell-cell fusion. Moreover, we highlight the areas for exploration of Myomaker and Myomixer-Myomerger-Minion in future studies and consider their potential application to control cell fusion for cell-therapy purposes.

Triploidy in zebrafish larvae: Effects on gene expression, cell size and cell number, growth, development and swimming performance

There is renewed interest in the regulation and consequences of cell size adaptations in studies on understanding the ecophysiology of ectotherms. Here we test if induction of triploidy, which increases cell size in zebrafish (Danio rerio), makes for a good model system to study consequences of cell size. Ideally, diploid and triploid zebrafish should differ in cell size, but should otherwise be comparable in order to be suitable as a model. We induced triploidy by cold shock and compared diploid and triploid zebrafish larvae under standard rearing conditions for differences in genome size, cell size and cell number, development, growth and swimming performance and expression of housekeeping genes and hsp70.1. Triploid zebrafish have larger but fewer cells, and the increase in cell size matched the increase in genome size (+ 50%). Under standard conditions, patterns in gene expression, ontogenetic development and larval growth were near identical between triploids and diploids. However, under demanding conditions (i.e. the maximum swimming velocity during an escape response), triploid larvae performed poorer than their diploid counterparts, especially after repeated stimuli to induce swimming. This result is consistent with the idea that larger cells have less capacity to generate energy, which becomes manifest during repeated physical exertion resulting in increased fatigue. Triploidy induction in zebrafish appears a valid method to increase specifically cell size and this provides a model system to test for consequences of cell size adaptation for the energy budget and swimming performance of this ectothermic vertebrate.

Physiological functions of CKIP-1: From molecular mechanisms to therapy implications

The casein kinase 2 interacting protein-1 (CKIP-1, also known as PLEKHO1) is initially identified as a specific CK2α subunit-interacting protein. Subsequently, various proteins, including CPα, PAK1, Arp2/3, HDAC1, c-Jun, ATM, Smurf1, Rpt6, Akt, IFP35, TRAF6, REGγ and CARMA1, were reported to interact with CKIP-1. Owing to the great diversity of interacted proteins, CKIP-1 exhibits multiple biologic functions in cell morphology, cell differentiation and cell apoptosis. Besides, these functions are subcellular localization, cell type, and regulatory signaling dependent. CKIP-1 is involved in biological processes consisting of bone formation, tumorigenesis and immune regulation. Importantly, deregulation of CKIP-1 results in osteoporosis, tumor, and atherosclerosis. In this review, we introduce the molecular functions, biological processes and promising of therapeutic strategies. Through summarizing the intrinsic mechanisms, we expect to open new therapeutic avenues for CKIP-1.

Effects of constrained dynamic loading, CKIP‑1 gene knockout and combination stimulations on bone loss caused by mechanical unloading

Mechanical stimulation plays an important role in maintaining the growth and normal function of the skeletal system. Mechanical unloading occurs, for example, in astronauts spending long periods of time in space or in patients on prolonged bed rest, and causes a rapid loss of bone mass. Casein kinase 2‑interacting protein‑1 (CKIP‑1) is a novel negative bone regulation factor that has been demonstrated to reduce bone loss and enhance bone formation. The aim of this study was to investigate the effect of constrained dynamic loading (Loading) in combination with CKIP‑1 gene knockout (KO) on unloading‑induced bone loss in tail‑suspension mice. The blood serum metabolism index [alkaline phosphatase (ALP) activity and osteocalcin (OCN) levels], tibia mechanical behavior (including bone trabecular microstructure parameters and tibia biomechanical properties), osteoblast‑related gene expression [ALP, OCN, collagen I and bone morphogenetic protein‑2 and osteoprotegerin (OPG)] and osteoclast‑related gene expression [receptor activators of NF‑kB ligand (RANKL)] were measured. The results demonstrated that mice experienced a loss of bone mass after four weeks of tail suspension compared with a wild type group. The mechanical properties, microarchitecture and mRNA expression were significantly increased in mice after Loading + KO treatment (P<0.05). Furthermore, compared with loading or KO alone, the ratio of OPG/RANKL was increased in the combined treatment group. The combined effect of Loading + KO was greater than that observed with loading or KO alone (P<0.05). The present study demonstrates that Loading + KO can counter unloading‑induced bone loss, and combining the two treatments has an additive effect. These results indicate that combined therapy could be a novel strategy for the clinical treatment of disuse osteoporosis associated with space travel or bed rest.

Association of CKIP-1 P21A polymorphism with risk of chronic heart failure in a Chinese population

Pathological cardiac hypertrophy is an independent risk factor for chronic heart failure. Casein kinase-2 interacting protein-1 (CKIP-1) can inhibit pathological cardiac hypertrophy. Therefore, we investigated whether CKIP-1 nonsynonymous polymorphism rs2306235 (Pro21Ala) contributes to risk and prognosis of chronic heart failure in a Chinese population.A total of 923 adult patients with chronic heart failure and 1020 age- and gender-matched healthy controls were recruited. CKIP-1 rs2306235 polymorphism was genotyped using PCR-restriction fragment length polymorphism. Additional follow-up data for 140 chronic heart failure patients was evaluated. The rs2306235 G allele was associated with an increased risk of chronic heart failure (OR = 1.38, 95% CI = 1.09-1.75, p = 0.007), especially in patients with hypertension (OR = 1.45, 95% CI = 1.09-1.75, p = 0.006) and coronary heart disease (OR = 1.41, 95% CI = 1.09-1.83, p = 0.010) after adjustment for multiple cardiovascular risk factors. However, rs2306235 polymorphism was not associated with cardiovascular mortality in chronic heart failure (p = 0.875). CKIP-1 rs2306235 polymorphism may be a risk factor for chronic heart failure in a Chinese Han population.

Acting on identity: Myoblast fusion and the formation of the syncytial muscle fiber

The study of Drosophila muscle development dates back to the middle of the last century. Since that time, Drosophila has proved to be an ideal system for studying muscle development, differentiation, function, and disease. As in humans, Drosophila muscle forms via a series of conserved steps, starting with muscle specification, myoblast fusion, attachment to tendon cells, interactions with motorneurons, and sarcomere and myofibril formation. The genes and mechanisms required for these processes share striking similarities to those found in humans. The highly tractable genetic system and imaging approaches available in Drosophila allow for an efficient interrogation of muscle biology and for application of what we learn to other systems. In this article, we review our current understanding of muscle development in Drosophila, with a focus on myoblast fusion, the process responsible for the generation of syncytial muscle cells. We also compare and contrast those genes required for fusion in Drosophila and vertebrates.

Targeted Lipidomic Analysis of Myoblasts by GC-MS and LC-MS/MS

Lipids represent ∼10% of the cell dry mass and play essential roles in membrane composition and physical properties, energy storage, and signaling pathways. In the developing or the regenerating skeletal muscle, modifications in the content or the flipping between leaflets of membrane lipid components can modulate the fusion capacity of myoblasts, thus constituting one of the regulatory mechanisms underlying myofiber growth. Recently, few genes controlling these qualitative and quantitative modifications have started to be unraveled. The precise functional characterization of these genes requires both qualitative and quantitative evaluations of a global lipid profile. Here, we describe a lipidomic protocol using mass spectrometry, allowing assessing the content of fatty acids, glycerophospholipids, and cholesterol in the routinely used C2C12 mouse myoblast cell line, or in primary cultures of mouse myoblasts.

Noncanonical roles for Tropomyosin during myogenesis

For skeletal muscle to produce movement, individual myofibers must form stable contacts with tendon cells and then assemble sarcomeres. The myofiber precursor is the nascent myotube, and during myogenesis the myotube completes guided elongation to reach its target tendons. Unlike the well-studied events of myogenesis, such as myoblast specification and myoblast fusion, the molecules that regulate myotube elongation are largely unknown. In Drosophila, hoi polloi (hoip) encodes a highly conserved RNA-binding protein and hoip mutant embryos are largely paralytic due to defects in myotube elongation and sarcomeric protein expression. We used the hoip mutant background as a platform to identify novel regulators of myogenesis, and uncovered surprising developmental functions for the sarcomeric protein Tropomyosin 2 (Tm2). We have identified Hoip-responsive sequences in the coding region of the Tm2 mRNA that are essential for Tm2 protein expression in developing myotubes. Tm2 overexpression rescued the hoip myogenic phenotype by promoting F-actin assembly at the myotube leading edge, by restoring the expression of additional sarcomeric RNAs, and by promoting myoblast fusion. Embryos that lack Tm2 also showed reduced sarcomeric protein expression, and embryos that expressed a gain-of-function Tm2 allele showed both fusion and elongation defects. Tropomyosin therefore dictates fundamental steps of myogenesis prior to regulating contraction in the sarcomere.

The Role of the Pleckstrin Homology Domain-containing Protein CKIP-1 in Activation of p21-activated Kinase 1 (PAK1)

Upon growth factor stimulation, PAK1 is recruited to the plasma membrane and activated by a mechanism that requires its phosphorylation at Ser-223 by the protein kinase CK2. However, the upstream signaling molecules that regulate this phosphorylation event are not clearly defined. Here, we demonstrate a major role of the CK2α-interacting protein CKIP-1 in activation of PAK1. CK2α, CKIP-1, and PAK1 are translocated to membrane ruffles in response to the epidermal growth factor (EGF), where CKIP-1 mediates the interaction between CK2α and PAK1 in a PI3K-dependent manner. Consistently, PAK1 mediates phosphorylation and modulation of the activity of p41-Arc, one of its plasma membrane substrate, in a fashion that requires PI3K and CKIP-1. Moreover, CKIP-1 knockdown or PI3K inhibition suppresses PAK1-mediated cell migration and invasion, demonstrating the physiological significance of the PI3K-CKIP-1-CK2-PAK1 signaling pathway. Taken together, these findings identify a novel mechanism for the activation of PAK1 at the plasma membrane, which is critical for cell migration and invasion.

Mechanisms of myoblast fusion during muscle development

The development and regeneration of skeletal muscle require the fusion of mononucleated muscle cells to form multinucleated, contractile muscle fibers. Studies using a simple genetic model, Drosophila melanogaster, have discovered many evolutionarily conserved fusion-promoting factors in vivo. Recent work in zebrafish and mouse also identified several vertebrate-specific factors required for myoblast fusion. Here, we integrate progress in multiple in vivo systems and highlight conceptual advance in understanding how muscle cell membranes are brought together for fusion. We focus on the molecular machinery at the fusogenic synapse and present a three-step model to describe the molecular and cellular events leading to fusion pore formation.

CKIP-1 suppresses the adipogenesis of mesenchymal stem cells by enhancing HDAC1-associated repression of C/EBPα

Mesenchymal stem cells (MSCs) are considered as the developmental origin of multiple lineage cells including osteocytes, adipocytes, and muscle cells. Previous studies demonstrated that the PH domain-containing protein CKIP-1 plays an important role in the development of osteoblasts and cardiomyocytes. However, whether CKIP-1 is involved in the generation of adipocytes as well as the MSC differentiation remains unknown. Here we show that CKIP-1 is a novel regulator of MSCs differentiating into adipocytes. MSCs derived from CKIP-1-deficient mice display enhanced adipogenesis upon induction. Further analysis showed that CKIP-1 interacts with the histone deacetylase HDAC1 in the nucleus and inhibits the transcription of CCAAT/enhancer-binding protein α (C/EBPα), which is a crucial adipogenic transcription factor. Ectopic expression of CKIP-1 in a MSC-like cell line C3H/10T1/2 reduced the generation of adipocytes due to suppression of adipogenic factors, including C/EBPα. Moreover, CKIP-1-deficient mice showed an increase in body weight and white adipose tissue gains when fed on a high-fat diet. Collectively, these results suggest that CKIP-1 is a novel inhibitor of MSC-originated adipogenesis by enhancing HDAC1-associated repression of C/EBPα.

Capping protein regulators fine-tune actin assembly dynamics

Capping protein (CP) binds the fast growing barbed end of the actin filament and regulates actin assembly by blocking the addition and loss of actin subunits. Recent studies provide new insights into how CP and barbed-end capping are regulated. Filament elongation factors, such as formins and ENA/VASP (enabled/vasodilator-stimulated phosphoprotein), indirectly regulate CP by competing with CP for binding to the barbed end, whereas other molecules, including V-1 and phospholipids, directly bind to CP and sterically block its interaction with the filament. In addition, a diverse and unrelated group of proteins interact with CP through a conserved 'capping protein interaction' (CPI) motif. These proteins, including CARMIL (capping protein, ARP2/3 and myosin I linker), CD2AP (CD2-associated protein) and the WASH (WASP and SCAR homologue) complex subunit FAM21, recruit CP to specific subcellular locations and modulate its actin-capping activity via allosteric effects.

Control of muscle fibre-type diversity during embryonic development: the zebrafish paradigm

Vertebrate skeletal muscle is composed of distinct types of fibre that are functionally adapted through differences in their physiological and metabolic properties. An understanding of the molecular basis of fibre-type specification is of relevance to human health and fitness. The zebrafish provides an attractive model for investigating fibre type specification; not only are their rapidly developing embryos optically transparent, but in contrast to amniotes, the embryonic myotome shows a discrete temporal and spatial separation of fibre type ontogeny that simplifies its analysis. Here we review the current state of understanding of muscle fibre type specification and differentiation during embryonic development of the zebrafish, with a particular focus on the roles of the Prdm1a and Sox6 transcription factors, and consider the relevance of these findings to higher vertebrate muscle biology.