Expression profile analyses of mettl8 in Oryzias latipes

Methyltransferase-like 8 (mettl8) is a protein-coding gene that may demonstrate nucleic acid or protein methyltransferase activity. Although several members of the METTL protein family have been reported, the expression and function of this family are still poorly understood, especially in fish. Medaka (Oryzias latipes) is an important model organism with relatively complete genome information, and more and more genetic toolkits are available for this fish. The popularity of medaka among developmental biologists has led to important insights into vertebrate development. Here, we report the DNA sequence and expression of mettl8 in medaka. The full-length cDNA of medaka mettl8 is 1266 bp, and its predicted open reading frame codes for a protein with 393 amino acids. The predicted molecular mass was 45.8 kDa, and the theoretical isoelectric point was 8.61. It had a conserved methyltransferase domain in METTL8 proteins. Homology analysis revealed that medaka METTL8 clustered in close proximity with the METTL8 of Austrofundulus limnaeus and Nothobranchius furzeri within the Cyprinodontiformes branch, and the protein structure of METTL8 was highly conserved. During embryogenesis, the mettl8 transcript was highly expressed in early stages, while it persisted at a detectable level until the larvae stage. In adult fish, the RT-PCR result indicated that mettl8 mRNA was expressed in the brain, eye, skin, liver, intestine, ovary, and testis. Slice in situ hybridization analysis showed that mettl8 was highly expressed in the eye, intestine, ovary, and testis. The expression and distribution of mettl8 during embryogenesis were also demonstrated by whole mount in situ hybridization. The results indicated that the mettl8 is expressed significantly in the eye, somite, and otic vesicles. Immunofluorescence and Western blot analyses showed that METTL8 protein was present in both the nuclei and cytoplasm. This study lays a foundation for further research on the function of fish mettl8.