Current Research, Industrialization Status, and Future Perspective of Cultured Meat

Expectations for the industrialization of cultured meat are growing due to the increasing support from various sectors, such as the food industry, animal welfare organizations, and consumers, particularly vegetarians, but the progress of industrialization is slower than initially reported. This review analyzes the main issues concerning the industrialization of cultured meat, examines research and media reports on the development of cultured meat to date, and presents the current technology, industrialization level, and prospects for cultured meat. Currently, over 30 countries have companies industrializing cultured meat, and around 200 companies that are developing or industrializing cultured meat have been surveyed globally. By country, the United States has over 50 companies, accounting for more than 20% of the total. Acquiring animal cells, developing cell lines, improving cell proliferation, improving the efficiency of cell differentiation and muscle production, or developing cell culture media, including serum-free media, are the major research themes related to the development of cultured meat. In contrast, the development of devices, such as bioreactors, which are crucial in enabling large-scale production, is relatively understudied, and few of the many companies invested in the development of cultured meat have presented products for sale other than prototypes. In addition, because most information on key technologies is not publicly available, it is not possible to determine the level of technology in the companies, and it is surmised that the technology of cultured meat-related startups is not high. Therefore, further research and development are needed to promote the full-scale industrialization of cultured meat.

Life Course Impact of Glucocorticoids During Pregnancy on Muscle Development and Function

Maternal stress, such as maternal obesity, can induce severe gestational disease and hormonal disorder which may disrupt fetal organ maturation and further cause endangered early or future health in offspring. During fetal development, glucocorticoids are essential for the maturation of organ systems. For instance, in clinical applications, glucocorticoids are commonly utilized to pregnant women with the risk of preterm delivery to reduce mortality of the newborns. However, exposure of excessive glucocorticoids at embryonic and fetal developmental stages can cause diseases such as cardiovascular disease and muscle atrophy in adulthood. Effects of excessive glucocorticoids on human health are well-recognized and extensively studied. Nonetheless, effects of these hormones on farm animal growth and development, particularly on prenatal muscle development, and postnatal growth, did not attract much attention until the last decade. Here, we provided a short review of the recent progress relating to the effect of glucocorticoids on prenatal skeletal muscle development and postnatal muscle growth as well as heart muscle development and cardiovascular disease during life course.

Cortisol differentially affects the viability and myogenesis of mono- and co-cultured porcine gluteal muscles satellite cells and fibroblasts

Cortisol is a ubiquitously expressed stress hormone. In this study, we investigated the effects of exogenous cortisol on porcine gluteal muscles primary cultured satellite cells and fibroblasts. Satellite cells and fibroblasts were mono-or co-cultured, and cells in each type of culture were categorized into the control and cortisol-treated (treatment) groups. We selected 28 μmol mL^-1 cortisol for treatment based on their efficacy. Cortisol treatment reduced viability of monocultured satellite cells and fibroblasts. In both monocultured and co-cultured cells, the nucleus in the treatment group was damaged than that control group. Moreover, the total cell cycle duration was shorter in the treatment group than the control group. PAX-7 expression was upregulated in the control group of co-cultured satellite cells and fibroblasts than those remaining groups. Moreover, MyoD expression was downregulated in the cortisol treated group of both mono-and co-cultured satellite cells compared with that in the control group. In co-cultured fibroblasts, MyoD and MyoG expression was upregulated than those remaining groups. The Cyto-C expression was upregulated in the treatment group compared to the control mono-and co-cultured both cells. These results suggest that the selected experimental dose of cortisol reduced cell viability and myogenesis-related gene expression in the monoculture compared to that in the co-culture of satellite cells and fibroblasts.

Identification and Characterization of lncRNAs Related to the Muscle Growth and Development of Japanese Flounder (Paralichthys olivaceus)

Long noncoding RNAs (lncRNAs) play an important role in many life activities, but the expression pattern and function of lncRNAs in Japanese flounder skeletal muscle are unclear. In this study, 751 lncRNAs were selected from skeletal muscle in different development stages of the Japanese flounder [stage A: larval 7 days post hatching (dph); stage B: juvenile about 90 dph; stage C (female) and stage D (male): adult about 24 months] using coding potential analysis methods. In total, 232, 211, 194, 28, 29, and 14 differentially expressed lncRNAs and 9549, 8673, 9181, 1821, 1080, and 557 differentially expressed mRNAs were identified in comparisons of A versus B, A versus C, A versus D, B versus C, B versus D, and C versus D, respectively. We identified the cis- and trans-regulatory target genes of differentially expressed lncRNAs, and lncRNA-gene interaction networks were constructed using the Cytoscape program. In total, there were 200, 200, 200, 93, 47, and 11 cis-regulation relationships, and 29, 19, 24, 38, 8, and 47 trans-regulation relationships in the comparisons between A versus B, A versus C, A versus D, B versus C, B versus D, and C versus D, respectively. These results indicate that lncRNA may participate in the development of Japanese flounder skeletal muscle through cis- or trans-acting mechanisms, thus providing a scientific basis for further study of the biological function of lncRNA in Japanese flounder skeletal muscle. Based on these relationships, functional annotation of the related lncRNAs was performed by gene ontology and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis. Differentially expressed genes associated with muscle development were enriched in multiple pairs of comparisons (e.g., differentially expressed genes LOC109640370, LOC109634180, LOC109643555, rusc1, and LOC109626999 were enriched in the actin-binding term, and differentially expressed genes LOC109640370, was, LOC109644970, LOC109643555, and itga9 were enriched in the regulation of the actin cytoskeleton pathway in the KEGG pathway analysis in the comparison of stages C and D). We predicted lncRNA-mRNA, miRNA-mRNA, and lncRNA-miRNA regulatory relationships and constructed interactive networks using Cytoscape software. Co-expression networks show that most lncRNAs interact with one or two predicted miRNAs involved in muscle growth and development. These results provide a basis for further study of the function of lncRNAs on skeletal muscle in different developmental stages of Japanese flounder.

Gene expression of Hanwoo satellite cell differentiation in longissimus dorsi and semimembranosus

BACKGROUND

Korean Hanwoo cattle are known for their high meat quality, especially their high intramuscular fat compared to most other cattle breeds. Different muscles have very different meat quality traits and a study of the myogenic process in satellite cells can help us better understand the genes and pathways that regulate this process and how muscles differentiate.

RESULTS

Cell cultures of Longissimus dorsi muscle differentiated from myoblast into multinucleated myotubes faster than semimembranosus. Time-series RNA-seq identified a total of 13 differentially expressed genes between the two muscles during their development. These genes seem to be involved in determining muscle lineage development and appear to modulate the expression of myogenic regulatory factors (mainly MYOD and MYF5) during differentiation of satellite cells into multinucleate myotubes. Gene ontology enriched terms were consistent with the morphological changes observed in the histology. Most of the over-represented terms and genes expressed during myoblast differentiation were similar regardless of muscle type which indicates a highly conserved myogenic process albeit the rates of differentiation being different. There were more differences in the enriched GO terms during the end of proliferation compared to myoblast differentiation.

CONCLUSIONS

The use of satellite cells from newborn Hanwoo calves appears to be a good model to study embryonic myogenesis in muscle. Our findings provide evidence that the differential expression of HOXB2, HOXB4, HOXB9, HOXC8, FOXD1, IGFN1, ZIC2, ZIC4, HOXA11, HOXC11, PITX1, SIM2 and TBX4 genes could be involved in the differentiation of Longissimus dorsi and Semimembranosus muscles. These genes seem to modulate the muscle fate of the satellite cells during myogenesis through a differential expression profile that also controls the expression of some myogenic regulatory factors (MYOD and MYF5). The number of differentially expressed genes across time was unsurprisingly large. In relation to the baseline day 0, there were 631, 155, 175, 519 and 586 DE genes in LD, while in SM we found 204, 0, 615, 761 and 1154 DE genes at days 1, 2, 4, 7 and 14 respectively.

The novel 22 bp insertion mutation in a promoter region of the <i>PITX2</i> gene is associated with litter size and growth traits in goats

Abstract. The paired-like homeodomain 2 (PITX2) gene plays a critical role in regulating development, reproduction, and growth traits in ruminants. Hence, the objective of this study was to explore the polymorphisms of this gene and to evaluate their associations with quantitative traits. Herein, a novel insertion in the promoter region of the PITX2 gene was reported in Shaanbei white cashmere (SBWC) goats (n=1012). The genotype distributions between mothers of single-kid and multi-kid groups within SBWC goats were significantly different (P<0.01), implying that this indel mutation might affect the litter size. Furthermore, association analysis found that this indel mutation was significantly associated with litter size (P=0.001). Individuals with genotype DD had a significantly smaller litter size than those with other genotypes (P<0.01). Besides, this indel was significantly associated with the body length (P=0.042) and the chest width (P=0.031). Especially, the individuals with genotype DD had a significantly lower body length than those with genotype II (P<0.05), which was consistent with the trend in litter size. These findings suggested that the new 22 bp indel mutation within the PITX2 gene is significantly associated with litter size and growth traits; this can be utilized as a functional molecular marker in goat breeding.

Dynamic transcriptomic analysis in hircine longissimus dorsi muscle from fetal to neonatal development stages

Muscle growth and development from fetal to neonatal stages consist of a series of delicately regulated and orchestrated changes in expression of genes. In this study, we performed whole transcriptome profiling based on RNA-Seq of caprine longissimus dorsi muscle tissue obtained from prenatal stages (days 45, 60, and 105 of gestation) and neonatal stage (the 3-day-old newborn) to identify genes that are differentially expressed and investigate their temporal expression profiles. A total of 3276 differentially expressed genes (DEGs) were identified (Q value < 0.01). Time-series expression profile clustering analysis indicated that DEGs were significantly clustered into eight clusters which can be divided into two classes (Q value < 0.05), class I profiles with downregulated patterns and class II profiles with upregulated patterns. Based on cluster analysis, GO enrichment analysis found that 75, 25, and 8 terms to be significantly enriched in biological process (BP), cellular component (CC), and molecular function (MF) categories in class I profiles, while 35, 21, and 8 terms to be significantly enriched in BP, CC, and MF in class II profiles. KEGG pathway analysis revealed that DEGs from class I profiles were significantly enriched in 22 pathways and the most enriched pathway was Rap1 signaling pathway. DEGs from class II profiles were significantly enriched in 17 pathways and the mainly enriched pathway was AMPK signaling pathway. Finally, six selected DEGs from our sequencing results were confirmed by qPCR. Our study provides a comprehensive understanding of the molecular mechanisms during goat skeletal muscle development from fetal to neonatal stages and valuable information for future studies of muscle development in goats.

Genome-wide identification and characterization of long non-coding RNAs in developmental skeletal muscle of fetal goat

Background

Long non-coding RNAs (lncRNAs) have been studied extensively over the past few years. Large numbers of lncRNAs have been identified in mouse, rat, and human, and some of them have been shown to play important roles in muscle development and myogenesis. However, there are few reports on the characterization of lncRNAs covering all the development stages of skeletal muscle in livestock.

Results

RNA libraries constructed from developing longissimus dorsi muscle of fetal (45, 60, and 105 days of gestation) and postnatal (3 days after birth) goat (Capra hircus) were sequenced. A total of 1,034,049,894 clean reads were generated. Among them, 3981 lncRNA transcripts corresponding to 2739 lncRNA genes were identified, including 3515 intergenic lncRNAs and 466 anti-sense lncRNAs. Notably, in pairwise comparisons between the libraries of skeletal muscle at the different development stages, a total of 577 transcripts were differentially expressed (P < 0.05) which were validated by qPCR using randomly selected six lncRNA genes. The identified goat lncRNAs shared some characteristics, such as fewer exons and shorter length, with the lncRNAs in other mammals. We also found 1153 lncRNAs genes were neighbored 1455 protein-coding genes (<10 kb upstream and downstream) and functionally enriched in transcriptional regulation and development-related processes, indicating they may be in cis-regulatory relationships. Additionally, Pearson’s correlation coefficients of co-expression levels suggested 1737 lncRNAs and 19,422 mRNAs were possibly in trans-regulatory relationships (r > 0.95 or r < −0.95). These co-expressed mRNAs were enriched in development-related biological processes such as muscle system processes, regulation of cell growth, muscle cell development, regulation of transcription, and embryonic morphogenesis.

Conclusions

This study provides a catalog of goat muscle-related lncRNAs, and will contribute to a fuller understanding of the molecular mechanism underpinning muscle development in mammals.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-016-3009-3) contains supplementary material, which is available to authorized users.

The role of TORC1 in muscle development in Drosophila

Myogenesis is an important process during both development and muscle repair. Previous studies suggest that mTORC1 plays a role in the formation of mature muscle from immature muscle precursor cells. Here we show that gene expression for several myogenic transcription factors including Myf5, Myog and Mef2c but not MyoD and myosin heavy chain isoforms decrease when C2C12 cells are treated with rapamycin, supporting a role for mTORC1 pathway during muscle development. To investigate the possibility that mTORC1 can regulate muscle in vivo we ablated the essential dTORC1 subunit Raptor in Drosophila melanogaster and found that muscle-specific knockdown of Raptor causes flies to be too weak to emerge from their pupal cases during eclosion. Using a series of GAL4 drivers we also show that muscle-specific Raptor knockdown also causes shortened lifespan, even when eclosure is unaffected. Together these results highlight an important role for TORC1 in muscle development, integrity and function in both Drosophila and mammalian cells.