Miiuy Croaker Transferrin Gene and Evidence for Positive Selection Events Reveal Different Evolutionary Patterns

Abstract

Transferrin (TF) is a protein that plays a central role in iron metabolism. This protein is associated with the innate immune system, which is responsible for disease defense responses after bacterial infection. The clear link between TF and the immune defense mechanism has led researchers to consider TF as a candidate gene for disease resistance. In this study, the Miichthys miiuy (miiuy croaker) TF gene (MIMI-TF) was cloned and characterized. The gene structure consisted of a coding region of 2070 nucleotides divided into 17 exons, as well as a non-coding region that included 16 introns and spans 6757 nucleotides. The deduced MIMI-TF protein consisted of 689 amino acids that comprised a signal peptide and two lobes (N- and C-lobes). MIMI-TF expression was significantly up-regulated after infection with Vibrio anguillarum. A series of model tests implemented in the CODEML program showed that TF underwent a complex evolutionary process. Branch-site models revealed that vertebrate TF was vastly different from that of invertebrates, and that the TF of the ancestors of aquatic and terrestrial organisms underwent different selection pressures. The site models detected 10 positively selected sites in extant TF genes. One site was located in the cleft between the N1 and N2 domains and was expected to affect the capability of TF to bind to or release iron indirectly. In addition, eight sites were found near the TF exterior. Two of these sites, which could have evolved from the competition for iron between pathogenic bacteria and TF, were located in potential pathogen-binding domains. Our results could be used to further investigate the function of TF and the selective mechanisms involved.

The Megalobrama amblycephala transferrin and transferrin receptor genes: Molecular cloning, characterization and expression during early development and after Aeromonas hydrophila infection

“…Iron-bound TF interacts with TFR, forms the TF-receptor complex, and iron is delivered into cells via the endocytosis process of TFR. Consistent with previous studies (Gao et al, 2013;Liu et al, 2010;Sun et al, 2012), the M. amblycephala Tf mRNA was the most abundant in the liver, the primary organ of TF synthesis (Beutler et al, 2000). In horse, the highest expression of TfR was detected in bone marrow, the primary hemopoietic tissue in mammals, consistent with its role of uptaking iron for hemoglobin synthesis (Webb et al, 2010).…”

“…According to previous studies, the up-regulation of TfR implies that the endocytosis of TF-bound iron increases to limit the iron availability for pathogen proliferation. In the present study, immunohistochemical analysis and iron staining verified the internalization of TF-receptor system with bound-iron in the liver of M. amblycephala, suggesting that the induced expression of TF/ TFR pathway signified their involvement in immune responses against pathogen invasion Neves et al, 2009Neves et al, , 2011Sun et al, 2012).…”

“…TF is mainly synthesized in the liver, but may also be expressed in other tissues, such as blood in Chinese black sleeper (Gao et al, 2013), brain in sea bass (Neves et al, 2009), and muscle in Miiuy croaker (Sun et al, 2012). TF contains two homologous globular domains: the N-lobe and the C-lobe, which are linked by an inter-domain bridge.…”

Transferrin in fishes: A review article

“…Generally, as an acute-phase protein in fish, the concentration of transferrin indicates the condition of infection or stress, though its rise or fall varies with the infective microorganisms or injury in different tissues [2,40]. Transferrin is also involved in many biological functions, such as DNA synthesis, oxygen and electron transport, growth, differentiation and cytoprotection processes [8,13,55,[59][60][61]. Relatively recent data uncovered an additional role of transferrin as an upstream regulator of hepcidin, a liver-derived peptide hormone that controls systemic iron traffic [62].…”

Genetic diversity and population genetic structure of the miiuy croaker, Miichthys miiuy, in the East China Sea by microsatellite markers

“…In recent years, most studies on the miiuy croaker were about morphological and physiological characteristics and molecular immunology (Liu et al, 2007;Cheng et al, 2011a,b;Xu et al, 2011a,b;Meng et al, 2012;Sun et al, 2005Sun et al, , 2012. However, little is known about the genetics of the miiuy croaker.…”