1. Introduction
The Jeryak is the result of crossbreeding between Gannan yak and Jersey cattle. Numerous studies have demonstrated that from Jersey cattle for crossbreeding with Gannan yak, the hybrid offspring of Jeryaks exhibit significantly increased body size and weight, robust physique, strong adaptability, rapid growth and development [
1], which provides support for herders’ living production and pastoral economy [
2]. In view of this, exploring the molecular regulatory mechanisms of skeletal muscle development may provide a direction to improve the production performance of Jeryaks.
The economic value of mammals is evaluated based on the meat production and its quality, which is influenced by the growth of skeletal muscles [
3]. The growth of skeletal muscle is an intricate and accurate process, including the creation of fetal muscle fibers prior to delivery and the enlargement of muscle fibers after delivery [
4]. Furthermore, the regulation of numerous transcription factors is imperative for the growth of skeletal muscles [
5]. Muscle derived regulatory factors (
MRFs) and muscle cell enhancer 2 (
MEF2) are widely recognized as crucial elements in the growth and development of skeletal muscle, as evidenced by previous studies [
6,
7,
8]. And
PAX3 and
PAX7 act as regulatory factors that control the development of skeletal muscle by interacting with MRFs [
9]. Muscle growth inhibitor (
MSTN) has been identified as a specific negative regulatory factor involved in skeletal muscle development, which interacts with certain signaling pathways to inhibit the expression of
MRFs or
PAX [
10,
11]. Furthermore, the Wnt, MAPK, and PI3K-Akt signaling pathways play a pivotal role in myogenesis, regeneration and differentiation across multiple species including mice, chicken and humans [
12,
13,
14,
15,
16,
17]. In recent years, the advancements in high-throughput sequencing technology have revealed that skeletal muscle growth is influenced not only by protein-coding RNAs but also by non-coding RNAs (ncRNAs), specifically microRNAs (miRNAs). These ncRNAs play a significant role in various biological processes and are regulated through multiple mechanisms.
MiRNAs, a class of small RNAs that are highly conserved across evolutionary species, exert post-transcriptional regulation on target genes by either degrading or inhibiting the translation of specific messenger RNAs (mRNAs) [
18,
19]. It has been demonstrated to play a role in vital biological processes, including cell proliferation and differentiation [
20,
21,
22].Currently, a plethora of research studies have indicated that the abundant expression of muscle-specific miRNAs, such as miR-1, miR-206, miR-133, and miR-499, within skeletal muscles significantly influences their development [
23,
24,
25]. Chen et al. [
26] reported an observed notable increase in the levels of miR-1 and miR-206 during satellite cells differentiation in skeletal muscle, while a decrease was observed during the process of skeletal muscle regeneration. Further investigation unveiled that miR-1/206 exerted inhibitory effects on the expression of
Pax7, thereby hindering the proliferation and differentiation of satellite cells. Nakasa et al.[
27] showed that the activation of
MyoD,
MyoG and
Pax7 occurred when miR-1, miR-133, and miR-206 were injected together at the site of muscle injury in rats and this activation subsequently facilitated muscle regeneration and suppressed muscle fibrosis. Meanwhile, MiR-499 has been demonstrated its significance in regulating the composition of muscle fibers [
28]. Additionally, miR-22-3p impedes the proliferation of skeletal muscle cells and promotes cellular differentiation by virtue of its interaction with
IGFBP3 [
29]. The identified interactions between oar-mir-655-3p and oar-mir-381-5p with
ACSM3 and
ABAT play a crucial role in the process of muscle organogenesis and myoblast migration in sheep [
30]. In recent years, transcriptome sequencing has been extensively explored to investigate the correlation between miRNAs and mRNAs in skeletal muscle development. However, the regulatory mechanisms governing miRNA-mRNA interaction in relation to Jeryaks muscle growth and development have yet to be investigated.
Therefore, in this study, we generated six small RNA libraries by collecting samples from the longissimus dorsi muscle of adult Gannan yaks and Jeryaks. By employing high-throughput sequencing and conducting comprehensive bioinformatics analysis, we elucidated the expression patterns of miRNA and mRNA, ultimately constructing intricate miRNA-mRNA regulatory networks between miRNA and mRNAs that are relevant to muscle growth. These findings help us to deepen our understanding of the hybrid dominance of Jeryaks and provide a theoretical basis for further research on the regulatory mechanisms of miRNAs associated with Jeryak muscle growth and development.
4. Discussion
Muscle growth is a multifaceted economic characteristic that not only impacts the quality of meat from livestock and poultry, but also plays a pivotal role in enhancing overall meat production performance[
36,
37]. Compared to conventional bovines, yaks exhibit a slower growth rate and have relatively modest production performance[
38]. Therefore, the quest for strategies to optimize yak productivity continues to be a pressing inquiry in need of resolution. Jeryak, a hybrid breed resulting from crossbreed of Gannan yak and Jersey cattle, have exhibited enhanced production capabilities in comparison to Gannan yak[
39]. Hence, investigating the molecular regulatory mechanism underlying this phenomenon will contribute to enhancing the economic advantages associated with yaks.
As widely acknowledged, the process of muscle growth is intricately governed by pivotal genes and their associated signaling pathways[
40,
41]. A total of 1819 DEMs were identified (FDR < 0.05) in this study. Despite the limited sample size of this study, a plethora of genes with different molecular functions were identified, thereby providing a valuable reference for investigating the signaling pathways associated with the longest dorsal muscle in Jeryak. In this study, a number of GO terms and KEGG pathways have been identified as closely associated with the process of muscle growth Examples include skeletal muscle cell differentiation, skeletal muscle tissue development and, MAPK and the signaling pathway. Notably, the background genes associated with these pathways have also been found to be involved in muscle growth and development of muscles, including
MEF2C,
SIX1,
CFL2, and
FGF6. It has been shown that the
MEF2C gene plays an active role in skeletal muscle differentiation and regeneration [
42,
43]. Yang et al. [
44]. demonstrated that knockdown of the
MEF2C gene inhibited myogenic differentiation of myoblasts, and conversely, overexpression of
MEF2C promoted their differentiation. In addition, the
Six1 gene, a potent regulator of skeletal muscle development [
45], activates myogenesis and enhances
Myf3 expression by specifically binding to the
MEF5 site in the promoter of the gene, thereby promoting skeletal muscle development [
46,
47]. Sun et al. [
48]. reported a significant upregulation of
CFL2 expression in skeletal muscle, which plays a crucial in regulating the activity of transcription factors involved in muscle formation within C2C12 cells and this, in turn, has an impact on the proliferation and differentiation of myofibroblasts. Another study revealed a correlation between the inactivation of
FGF6 and impaired muscle damage repair, as well as reduced expression of
MyoD and
MyoG in mutant mice and it was suggested that this could be attributed to the inhibition of satellite cell proliferation and differentiation caused by the inactivation of
FGF6 [
49]. Although these studies have contributed to prediction of key gene the function and accuracy, further investigation is required to explore the regulation mechanisms of other functional differentially expressed mRNAs (DEMs) associated with muscle growth and development in the longest dorsal muscle.
MiRNAs, crucial non-coding regulators in post-transcriptional regulation, exert their influence on a plethora of biological processes including cell proliferation, apoptosis, and the development of tumors [
50]. A total of 230 miRNAs exhibited differential expression in the present study. Among these, a total of 135 (DE)miRNAs displayed noteworthy down-regulation in the longestissimus dorsi muscle of Jeryak, whereas 95 (DE)miRNAs were exhibited significant up-regulated. Performing GO and KEGG pathway enrichment analysis on differentially expressed miRNA target genes to investigate their potential functional roles. The GO enrichment results demonstrate that (DE)miRNA primarily participates in the regulation of Wnt signaling and developmental processes. Additionally, KEGG pathway analysis revealed significantly enrichment of some (DE)miRNA in key pathways including Ras signaling, MAPK signaling, Wnt signaling, and FoxO signaling. As a prominent pathway for miRNA target genes in Jeryak, the Ras signaling cascade has been documented to exert inhibitory effects on skeletal muscle myogenesis [
51]. The MAPK signaling pathway has the capacity to regulate biological processes via multiple mechanisms of activating or inhibiting associated factors [
52]. It has been found that activation of the p38/MAPK signaling pathway can contribute to the thickening of muscle fiber cross-section and the increase of muscle length by regulating the protein content in adult muscle fibers after birth, thereby increasing total muscle mass [
53,
54]. A previous study demonstrated that the Wnt signaling exerts direct control over the expression of myogenic regulatory factors (
MRFs) during l embryonic development in animals, thereby influencing muscle production [
55]. Additionally, the FoXO signaling pathway is also involved in muscle growth and development, and it leads to skeletal muscle atrophy primarily through protein degradation [
56]. Sandri et al. [
57]. demonstrated that FoXO induces skeletal muscle atrophies by upregulating the ubiquitin ligase Atrogin-1.
To further scrutinize the candidate miRNAs governing muscle growth and development in Jeryak, we successfully constructed a miRNA-mRNA interaction network based on the results of our comprehensive analysis of mRNAs and miRNAs. Significantly, the two newly identified miRNAs exhibited differential expression in both species. The function of their target genes may mediate the effects of these miRNAs on muscle growth and development. Within the intricate network of interactions, novel-m0036-3p and novel-m0037-3p were found to specifically target both
SIX2,
SIX1,
NDRG4,
STX4, and
CTCF genes.
SIX1 has been reported as a constituent of the vertebrate
SIX gene family. During vertebrate skeletal myogenesis and development, the
Six1 transcription factor exerts a transcriptional regulatory effect on the myogenic determinant gene family, thereby indirectly modulating downstream muscle development-related genes through its regulation of individual members of
MRFs [
58]. Recent investigation reveals that excessive expression of the transcription factor
SIX2 stimulates satellite cell growth in bovine skeletal muscles [
59]. Zhu et al. [
60]. reported that
NDRG2 treatment of C12C4 myoblasts activated the Akt/CREB signaling pathway and a significantly upregulated
MyoD and
MyoG gene expression, thereby promoting myoblast differentiation.
STX4, also known as Syntaxin 4, exhibits significant expression levels in the skeletal muscle tissue. Yoo et al. [
60] found that
STX4 enhanced the proliferation and differentiation of myoblasts by interacting with
CDO.
CTCF is critical for early embryonic development [
61].
CTCF has been found to be a factor involved in the regulation of myogenesis, which promotes muscle differentiation mainly by coordinating with
MRFs [
62]. Interestingly, we also identified
SIX2,
SIX1,
NDRG4,
STX4, and
CTCF as down-regulated DEMs. As a result, we speculated that these miRNAs might influence the growth and development of muscles by inhibiting the expression of DEMs associated with muscles.
In addition, related studies have shown that not only one miRNA can act on multiple mRNAs, but also multiple miRNAs can act on the same Mrna [
63]. Notably, our interaction network diagram showed that miR-339-x, miR-339-z, and miR-10926-z acted concurrently with
MICAL2, and miR-421-y and miR-450-x acted concurrently with
MEF2A. Therefore, we hypothesize that these miRNAs may bind specifically to target mRNAs and have an effect on Jeryak skeletal muscle growth and development. Future studies should involve validation of possible miRNA-mRNA targeting relationship pairs in subsequent studies to explore their mechanisms of action in skeletal muscle growth and development.
Author Contributions
Conceptualization, GDS and ZZD; Methodology, BYB, CZC, SBG,LXP and LJS; Validation, GDS, WYL, LZX, BYB, and LJS; Formal analysis, ZFF, GDS and WYL; Investigation, GDS, LJS, WYL, LZX and CZC; Sources, ZZD, HJ and HXM; Writing-original manuscript preparation, GDS; Writing-review and editing, GDS and ZZD; Supervision, WJQ and ZZD; Project Management, LX, LSB and ZZD; Funding Acquisition, HJ and ZZD. All authors have read and agree to the published version of the manuscript. The authors have read and agree to the published version of the manuscript.