A Potential Negative Regulatory Function of Myostatin in the Growth of the Pacific Abalone, Haliotis discus hannai

SIMPLE SUMMARY: The Haliotis discus hannai (H. discus hannai) is one of the most economically important species cultured in China. Currently, the problems of slow growth and small abalone sizes have become increasingly serious, causing economic losses to farmers. The most effective way to solve the problems of slow growth, miniaturization, and lack of large abalone is by molecular genetic manipulation to breed high-quality abalone that have rapid growth rates. Analyzing the genetic mechanism of abalone growth and discovering key functional genes are thus critical for this genetic improvement program. Many studies have confirmed that myostatin is an important regulator of muscle growth in animals. In this study, we investigated the molecular structure and function of hdh-myostatin in H. discus hannai. The results revealed that hdh-myostatin contained structural characteristics typical of the TGF-β superfamily and was involved in the regulation of growth. Our findings would help to clarify the role of hdh-myostatin in the regulation of abalone growth and provide a reference for the application of molecular markers of growth traits in mollusk breeding. ABSTRACT: Myostatin, also known as GDF8, is a member of the transforming growth factor-β (TGF-β) superfamily. In vertebrates, myostatin negatively regulates the growth of skeletal muscle. In invertebrates, it has been reported to be closely related to animal growth. However, knowledge concerning the molecular mechanisms involved in the myostatin regulation of molluscan growth is limited. In this study, we found that the hdh-myostatin open reading frame (ORF) comprised 1470 base pairs that encoded 489 amino acids and contained structural characteristics typical of the TGF-β superfamily, including a C-terminal signal peptide, a propeptide domain, and TGF-β region. Gene expression analysis revealed that hdh-myostatin mRNA was widely expressed at different levels in all of the examined tissues of Haliotis discus hannai. Nine single nucleotide polymorphisms (SNPs) were associated with the growth traits. RNA interference (RNAi) against hdh-myostatin mRNA significantly downregulated hdh-myostatin at days 1, 15, and 30 post injection, and the pattern was correlated with downregulation of the genes TGF-β receptor type-I (hdh-TβR I), activin receptor type-IIB (hdh-ActR IIB), and mothers against decapentaplegic 3 (hdh-Smad3). After one month of the RNAi experiment, the shell lengths and total weights increased in the abalone, Haliotis discus hannai. The results of qRT-PCR showed that the hdh-myostatin mRNA level was higher in the slow-growing group than in the fast-growing group. These results suggest that hdh-myostatin is involved in the regulation of growth, and that these SNPs would be informative for further studies on selective breeding in abalone.