Abstract
Myostatin (MSTN) negatively regulates muscle growth and development through inhibiting myoblast proliferation and differentiation. Five alternative splicing isoforms of MSTN (MSTN-A to MSTN-E) have been discovered in domestic avian species. MSTN-A has high expression in skeletal muscle and encodes the full-length peptide with anti-myogenic activity. Another isoform, MSTN-B, is also highly expressed in skeletal muscle and encodes a truncated peptide that has pro-myogenic capabilities in vitro, which include promoting the proliferation and differentiation of quail muscle precursor cells. The objective of this study was to investigate overexpression of MSTN-B in vivo by using two independent lines of transgenic Japanese quail with expression directed in the skeletal muscle. Unexpectedly, the chicken skeletal muscle alpha actin 1 (cACTA1) promoter resulted in restricted exogenous MSTN-B protein expression to certain skeletal muscles, such as the gastrocnemius and tibialis anterior, but not the pectoralis major muscle. Gastrocnemius weight as a percentage of body weight in transgenic quail was increased compared to non-transgenic quail at posthatch day 21 (D21) and posthatch D42. An increase in the size of the gastrocnemius in transgenic quail was attributed to an increase in fiber number but not fiber cross-sectional area (CSA). During embryonic development, paired box 7 (PAX7) expression was prolonged in the transgenic embryos, but other myogenic regulatory factors (MRFs) were unchanged after MSTN-B overexpression. Taken together, these data provide novel insights into the regulation of skeletal muscle development by alternative splicing mechanisms in avians.
Highlights
Poultry consumption in the United States has steadily increased throughout the years; discovering ways of improving muscle accretion is warranted
Of the five MSTN isoforms produced by alternative splicing in avians, two isoforms, MSTN-A and MSTN-B, are highly expressed in skeletal muscle [18,19]
In vitro studies revealed that MSTN-B, which encodes a truncated peptide containing a portion of the MSTN propeptide, enhanced proliferation and differentiation when overexpressed in quail muscle precursor cells [19], the pro-myogenic role of MSTN-B has not been studied in vivo
Summary
Poultry consumption in the United States has steadily increased throughout the years; discovering ways of improving muscle accretion is warranted. Genetic selection of domestic poultry species has greatly enhanced muscle growth [2], but further investigation of the cellular and molecular mechanisms involved in skeletal muscle development is required. The resulting peptide, known as pro-MSTN, undergoes three proteolytic processing events. Pro-MSTN dimerizes near the C-terminus and is systematically cleaved at the RXXR site by a calcium-dependent serine protease, known as furin, to generate the N-terminal propeptides and C-terminal receptor-binding domain [3]. The latent MSTN complex forms as the propeptides noncovalently bind the C-terminal region via a critical peptide sequence, which prevents MSTN from binding to its target receptor. Members of the bone morphogenetic protein-1/tolloid (BMP-1/TLD) family are metalloproteinases that can cleave the propeptides from the latent complex and release mature MSTN, which can bind activin receptor type 2B (ACVR2B) to induce the appropriate signaling cascade [4]
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