Molecular Cloning and Copy Number Variation of a Ferritin Subunit (Fth1) and Its Association with Growth in Freshwater Pearl Mussel Hyriopsis cumingii

Zhiyi Bai,Genhua Yue,Yiming Yuan,Jiale Li,Dana Davis

doi:10.1371/journal.pone.0022886

Abstract

Iron is one of the most important minor elements in the shells of bivalves. This study was designed to investigate the involvement of ferritin, the principal protein for iron storage, in shell growth. A novel ferritin subunit (Fth1) cDNA from the freshwater pearl mussel (Hyriopsis cumingii) was isolated and characterized. The complete cDNA contained 822 bp, with an open reading frame (ORF) of 525 bp, a 153 bp 5′ untranslated region (UTR) and a 144 bp 3′ UTR. The complete genomic DNA was 4125 bp, containing four exons and three introns. The ORF encoded a protein of 174 amino acids without a signal sequence. The deduced ferritin contained a highly conserved motif for the ferroxidase center comprising seven residues of a typical vertebrate heavy-chain ferritin. It contained one conserved iron associated residue (Try27) and iron-binding region signature 1 residues. The mRNA contained a 27 bp iron-responsive element with a typical stem-loop structure in the 5′-UTR position. Copy number variants (CNVs) of Fth1 in two populations (PY and JH) were detected using quantitative real-time PCR. Associations between CNVs and growth were also analyzed. The results showed that the copy number of the ferritin gene of in the diploid genome ranged from two to 12 in PY, and from two to six in JH. The copy number variation in PY was higher than that in JH. In terms of shell length, mussels with four copies of the ferritin gene grew faster than those with three copies (P<0.05), suggesting that CNVs in the ferritin gene are associated with growth in shell length and might be a useful molecular marker in selective breeding of H. cumingii.

Highlights

As a cofactor in many biochemical reactions, the trace element iron is important to all living organisms through its role in regulating metabolism, electron transport, oxidative phosphorylation and DNA biosynthesis [1]
We investigated whether the copy number of the ferritin gene differed between a wild population and a cultured population, and whether a functional relationship existed between copy number and growth in H. cumingii
The genomic structure of the ferritin gene was determined by sequencing the genomic fragment amplified by PCR

Summary

Introduction

As a cofactor in many biochemical reactions, the trace element iron is important to all living organisms through its role in regulating metabolism, electron transport, oxidative phosphorylation and DNA biosynthesis [1]. Iron homeostasis is important in living cells [1,2]. A major iron storage protein in living cells, plays a crucial role in intracellular iron homeostasis. Ferritin has 24 subunits, which form a hollow shell and can store up to 4,500 iron (III) atoms [3]. There are two types of ferritin subunit: the heavy chain (H) and the light chain (L). H-ferritin subunits occur in multiple forms in animals, plants and bacteria, while L-ferritin subunits are usually restricted to vertebrates [4,5]. Ferritin has been shown to be involved in many physiological activities such as development [6,7,8], immunity [9,10] and other cellular mechanisms [11,12,13]

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Results

Conclusion