Dietary sodium alginate administration enhances Mx gene expression of the tiger grouper, Epinephelus fuscoguttatus receiving poly I:C

The full-length complementary (c)DNA of the Mx gene was cloned from the spleen of the tiger grouper, Epinephelus fuscoguttatus, injected with poly I:C by reverse-transcription polymerase chain reaction (RT-PCR) and rapid amplification of cDNA ends (RACE) methods. The 2163-bp cDNA contained an open reading frame (ORF) of 1878 bp, a 42-bp 5′-untranslated region (UTR), and a 243-bp 3′-UTR including a stop codon (TAG), a poly A tail, and a putative polyadenylation signal (AATAAA) 14 bp upstream of the poly A tail. The ORF encoded a protein of 626 amino acids (aa) with a predicted molecular mass of 71.3 kDa and an estimated pI of 5.55. The grouper Mx sequence contained putative functional domains including a tripartite guanosine-5′-triphosphate (GTP)-binding motif (GDQSSGKS, DLPG, and TKPD), the signature of the dynamin family (LPRGSGIVTR), and a putative leucine zipper in the carboxyl-terminal end of the protein. Sequence comparison showed that the Mx gene of this grouper had overall respective identities of 70%–96%, 51%–56%, and 34% to those of teleosts, mammals, and the abalone (Haliotis discus discus), respectively. A phylogenetic analysis revealed that the cloned Mx (TGMx) from tiger grouper was more-correlated with orange-spotted grouper MxII (gMxII). TGMx was constitutively expressed in all tissues, and its expression was upregulated by poly I:C and lipopolysaccharide (LPS), especially after a poly I:C injection. The Mx expressions had significantly increased in the eyes, head kidney, spleen, intestines, liver and gills after the LPS injection, and in all tested tissues after the poly I:C injection as compared to the groupers injected with PBS. The quantitative real-time RT-PCR analysis showed that Mx mRNA expression in the spleen and head kidney of grouper fed a diet containing sodium alginate and then injected with poly I:C after 12 h significantly increased, compared to those of fish fed a control diet (without sodium alginate). We therefore recommend an LPS and poly I:C injection to induce TGMx expression which was further enhanced by dietary sodium alginate administration.

► Mx cDNA was cloned from Epinephelus fuscoguttatus.
► The Mx of E. fuscoguttatus has high identities with those of other teleost.
► Mx expression was observed in tested tissues, and was induced by LPS and poly I:C.
► The regulation of Mx in grouper was related to sodium alginate administration.