Myostatin (MSTN) and its Applications in Animal Breeding

Dr Wani A Ahad

M.V.ScAnimal Biotechnology

SKUAST-K  

Recent advancements in sequencing and genotyping technologies have enabled a rapid evolution in methods for meat animal selection.

New tools will become available for meat producers to implement in the endeavor to efficiently produce high quality meat for today’s consumer.

The ultimate objective of improving meat quality either by breeding or rearing factors.

Introduction

Introduction For genetic purposes, polymorphisms in some key genes have been reported for their association with meat quality traits.

The sequencing of the bovine genome has dramatically increased the number of available gene polymorphisms.

The association of these new polymorphisms with the variability in meat quality (e.g. tenderness, marbling) for different breeds in different rearing systems will be a very important issue.

For rearing purposes, global gene expression profiling at the mRNA or protein level has already shown that previously unsuspected genes may be associated either with muscle development or growth, and may lead to the development of new molecular indicators of tenderness or marbling.

Some of these genes are specifically regulated by genetic and nutritional factors or differ between different meat cuts.

(Hocquette et al., 2007)

Introduction

Genes influencing Growth traitsS.No. GENE CHROMOSOME

1 MSTN: Myostatin (GDF-8) 2

2 CAST: Calpastatin 5

3 CLPG: Callipyge 18

4 LEP: Leptin gene 3

5 Casein: α casein 6

6 GH: Growth Hormone 19

7 GHR: Bovine Growth Hormone Receptor 20

8 IGF-I: Insulin Like Growth Factor I 5

9 POU1F1: Pituitary Specific Transcription Factor-1 1

An Example for meat trait, a visibly distinct muscular hypertrophy, commonly known as double muscling, occurs with high frequency in the Belgian Blue and Piedmontese cattle breeds.

Kambadur et al ., (1997) have evaluated this gene as a candidate gene for double-muscling condition by cloning the bovine myostatin cDNA and examining the expression pattern and sequence of the gene in normal and double-muscled cattle.

Moreover, sequence analysis reveals mutations in heavy-muscled cattle of both breeds.

Contd…

Myostatin is almost only expressed in skeletal muscle. Myostatin could first be detected at day 9.5 post-coitum. Myostatin knock-out mice muscles weigh 2-3 times more than those of wild type animals. Hyperplasia (more fibres) and hypertrophy (larger fibres); more DNA.

(McPherron et al., 1997)

Discovery of Myostatin Gene (GDF-8)

WILD TYPE

KNOCK OUT MICE

Myostatin (MSTN/GDF8) is a member of the transforming growth factor-β super family.

It is produced by skeletal muscle and acts as a negative regulator of muscle growth.

It has an essential role in the regulation of muscle growth and meat quality.

(Zhang et al., 2013)

Myostatin Gene

MSTN gene The myosatin prepropeptide is made

up of 3 subunits:1. C-terminal peptide2. Signal Sequence3. N-terminal peptide

For myostatin to be in its active form:

It needs to cleaved free from the propeptide complex:• Protease.

MSTN geneLocation 2q11-q12

Size 6.2 kbp

Exons 3

Introns 2

Physiological Action Myostatin and Activin interact and activate a heterodimeric receptor complex, comprising activin receptor 2 (ACVR2) and activin receptor-like kinase 4 (ALK4).

Myostatin/activin signaling in myofibers is mediated by phosphorylation and nuclear translocation of Smad2 or Smad3 (Small mothers against decapentaplegic) transcription factors, and formation of heterodimers with Smad4.

Smad4 complex binds to the promoters in the target genes & forms a transcription repressor complex.

(Rehfeldt et al., 2000)

Contd… Myostatin represses the levels of myogenic regulatory factors

(MyoD, Myf4, Myf5 and myogenin), leading to the inhibition of

myogenic differentiation.

Myostatin inhibits myogenic differentiation factor (MyoD)

activity and expression via Smad 3 resulting the failure of the

myoblasts to differentiate into myotubes (Mature Muscle Fibers).

(Rehfeldt et al., 2000)

Myostatin also inhibits Akt (Protein Kinase B

/ Serine/theronine specific protein kinase).

That is responsible to cause Muscle

hypertrophy.

Through activation of protein synthesis.

(Sartori et al., 2014)

How does myostatin inhibit growth?

Furthermore, MSTN has been shown to

directly prevent Cell Cycle G1 to S phase

transition by decreasing the levels of Cyclin

dependent kinase complex 2 ( CDK2).

(McKoy et al., 2007)

Contd…

Myostatin inhibitors Obviously, bodybuilders are very keen to inhibit myostatin in order to promote muscle growth further. Like: MYOSTAT MYO-ZAP MYO BLAST MYO-X

Super TGF

MSTN gene Polymorphism Mutations in the MSTN gene can inactivate its expression or produce a non-functional protein, which leads to dramatic muscularity and a “double-muscling” phenomenon in many species.

(Grisolia et al., 2009) It has been considered as an important candidate gene for growth and development of domestic animals .

MSTN has a key role in muscle growth and is believed to have potential applications in breeding and animal husbandry.

(Supakorn, 2009; Zhang et al., 2012)

Natural Myostatin mutations occur

Natural myostatin mutations can occur as well: McPherron et al. (1997) found in Belgian Blue and Piedmontese cattle a natural myostatin mutation resulting in non-functional myostatin and increased muscle size.

Figure: A fullblood Belgian Blue bull showing the double muscling phenotype

(McPherron et al., 1997)

Contd…

Missense mutation g.368A>C (p.Lys49Thr) in Exon-1 has effects on the MSTN protein structure and on the biological function of the MSTN protein.

(Grobet et al., 1998)

(Beaver, 2006)

The genetic improvement of animals is a fundamental, incessant, and complex process.

Conclusion

In recent years many methods have been developed and tested.

The genetic polymorphism at the DNA sequence level has provided a large number of markers and revealed potential utility of application in animal breeding.

The invention of polymerase chain reaction (PCR) in accordance with the constantly increasing accuracy in DNA sequencing methods also represents a milestone in this endeavor.

Conclusion

Identification of myostatin polymorphisms that can interrupt function.

Opens the door for widespread screening of possible carrier animals and breeding.

Strategies that can take advantage of the useful nature of a myostatin knockout while selecting against undesirable companion traits.

Plans already underway to screen large numbers of various livestock breeds and species will help producers to identify the mutation within their own herds and develop a breeding strategy to maximize its potential.

Conclusion

With these varied approaches to exploiting myostatin mutations may represent a significant gain for several livestock industries.

The two century-long drive to explore myostatin has been a study in tenacity for the livestock industry in particular, embodying the best outcome of perseverance and creative problem solving.

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