Characterization of the promoter region of bovine SIX4 : Roles of E-box and MyoD in the regulation of basal transcription

Cloning, phylogenetic and expression analysis of two MyoDs in yellowtail kingfish (Seriola lalandi)

Yellowtail kingfish (Seriola lalandi) is a pelagic piscivore distributed circumglobally. Owing to its great market value, the growth mechanism of S. lalandi, including muscle development and growth, is a hot research topic. The myoblast determination protein (MyoD) gene has been shown to play an important role in formation of myoblasts and the function of somites in fish. The open reading frame (ORF) sequences of MyoD1 and MyoD2 in S. lalandi encoded 298 and 263 amino acids possessing three common characteristic domains, respectively, containing a myogenic basic domain, a bHLH domain, and a ser-rich region (helix III). S. lalandi MyoDs shared the highest identity with the MyoDs of S. dumerili. MyoDs are highly expressed in white muscle (P < 0.05) in S. lalandi. The expression level of MyoD1 mRNA was higher than that of MyoD2 mRNA during embryonic and early developmental stages, indicating that the two MyoD isoforms may have different roles in muscle formation. Moreover, the mRNA expression of MyoDs in the brain, pituitary, liver and muscle of endocrine growth axis were analyzed in the various sizes and ages stages. The expression levels of MyoDs in the different sizes and ages of S. lalandi showed that expression of both these genes was particularly high in 400-g fish and 2-year-old fish (P < 0.05). Moreover, the increases in the mRNA expression and plasma levels of growth hormone (GH) and insulin-like growth factor (IGF-I) were accompanied by an increase in mRNA expression of MyoDs, indicating the roles of GH and IGF-I in muscle development and growth of S. lalandi. Overall, the expression profiles of genes associated with muscle development are the first step taken towards deciphering fast growth mechanism in this important Seriola fish.

Roles of MEF2A and MyoG in the transcriptional regulation of bovine LATS2 gene

As an important downstream effector gene in the hippo signaling pathway, large tumor suppressor gene 2 (LATS2) is involved in cell proliferation and differentiation, organ size and tissue regeneration, and plays an important role in regulating the growth and development of animal muscles. The purpose of this study is to explore the temporal expression of bovine LATS2 gene, and determine the key transcription factors for regulating bovine LATS2 gene. The result showed that bovine LATS2 gene was highly expressed in liver and longissimus dorsi, and was up-regulated in infancy muscle. In addition, it was highly expressed on the 2th day during the differentiation stage of myoblast. The upstream 1.7 Kb sequence of the 5 'translation region of bovine LATS2 gene was cloned, and 7 different deletion fragments were amplified by the upstream primers. These fragments were constructed into double luciferase reporter vectors and transfected into myoblasts and myotubes cells, respectively to detect the core promoter regions. In addition, the key transcription factors of the core promoter sequence of the bovine LATS2 gene were analyzed and predicted by online software. Combining with site-directed mutations, siRNA interference and chromatin immunoprecipitation technology, it was identified that MEF2A and MyoG combined in core promoter region (-248/-56) to regulate the transcription activity of bovine LATS2 gene. The results have laid a theoretical foundation for exploring the molecular regulation mechanism of LATS2 gene in the process of muscle growth.

Tissue Expression Analysis, Cloning, and Characterization of the 5'-Regulatory Region of the Bovine LATS1 Gene

As a member of the large tumor suppressor (LATS) gene family, LATS1 plays an important role in regulating muscle growth and development. In this study, we determined the distinct exhibit patterns of tissue expression of bovine LATS1. Further, we determined the functional proximal minimal promoter of bovine LATS1 and identified the key transcription factors in the core promoter region to elucidate its molecular regulation mechanism. The results showed that bovine LATS1 was highly expressed in the longissimus thoracis and upregulation in infancy muscle. An electrophoretic mobility shift assay (EMSA) and chromatin immunoprecipitation (ChIP) assay in combination with site-directed mutation and small interfering RNA (siRNA) interference demonstrated that myogenic differentiation 1 (Myod1) and myocyte enhancer factor 2A (MEF2A) binding in the core promoter region (−298/−123 bp) play important roles in the transcriptional regulation of the bovine LATS1 promoter. Taken together, these interactions provide insight into the regulatory mechanisms of LATS1 transcription in mediating skeletal muscle growth in cattle.

Bovine CAPN3 core promoter initiates expression of foreign genes in skeletal muscle cells by MyoD transcriptional regulation

Activating foreign genes in bovine skeletal muscle is necessary in the study of the role of related genes in skeletal muscle development and the effects on skeletal muscle formation, especially in the study of transgenic cattle. At this time, a skeletal muscle-specific promoter should be selected to initiate a functional foreign gene. Here, calpain3 (CAPN3) was found to be highly expressed in skeletal muscle and skeletal muscle cells by real-time PCR. Next, 5' deletion analysis of the bovine CAPN3 promoter was performed and showed that Q5(-495/+40) region was the core promoter of the bovine CAPN3. A key regulatory site (-465/-453) in CAPN3 core promoter was associated with the transcription factor, MyoD, which is a skeletal muscle-specific transcription factor. Furthermore, the mRNA and protein expression levels of MyoD and CAPN3 were positively correlated during skeletal muscle cell differentiation. The overexpression of MyoD enhanced the activity of the bovine CAPN3 core promoter. The core promoter Q5(-495/+40) could drive the exogenous gene EGFP and the fat-specific expression gene PPARγ in skeletal muscle cells. In summary, our study obtained a bovine skeletal muscle-specific promoter and provided a basis for studying the role of functional genes in the growth and development of skeletal muscle. It also provides a basis for studying the transcriptional regulation mechanism of CAPN3.

Functional analysis of two MyoDs revealed their role in the activation of myomixer expression in yellowfin seabream (Acanthopagrus latus) (Hottuyn, 1782)

Myoblast determination protein (MyoD), a muscle-specific basic helix-loop-helix (bHLH) transcription factor, plays a pivotal role in regulating skeletal muscle growth and development. However, the regulation mechanism of MyoD has not been determined in marine fishes. In the present study, we isolated the MyoD1 (AlMyoD1) and MyoD2 (AlMyoD2) genomic sequences and analyzed the expression patterns in different tissues of yellowfin seabream (Acanthopagrus latus). The open reading frame (ORF) sequences of AlMyoD1 and AlMyoD2 encoded 297 and 271 amino acids possessing three common characteristic domains, respectively, containing a myogenic basic domain, a bHLH domain, and a ser-rich region (helix III). Phylogenetic and genome structure analyses exhibited classic phylogeny and highly conserved exon/intron architecture. Furthermore, the AlMyoD1 and AlMyoD2 transcription levels were higher in white muscle than in the other tissues. In order to further study AlMyoD function in muscle, promoter sequence analysis found that several E-box binding sites were present. Additionally, binding sites of Almyomixer involved in mammal myoblast fusion, which expression was also the highest in white muscle, were found in the promoter of AlMyoD. Pomoter activity assays further confirmed that both AlMyoD1 and AlMyoD2 can dramatically activate Almyomixer expression, and the AlMyoD1 M2 and AlMyoD2 M5 E-box binding sites were functionally important for Almyomixer transcription based on mutation analysis and electrophoretic mobile shift assays (EMSA). In summary, two MyoDs play a core role in Almyomixer regulation and may promote myofibre formation during muscle development and growth by regulating Almyomixer expression.