Abstract:Iridovirus has a wide infection spectrum in aquatic animals, which is harmful to aquaculture. In spotted knifejaw (Oplegnathus punctatus), iridovirus is the major factor causing large-scale mortality. Iridovirus infection results in high mortality rate and thus limits the development of the spotted knifejaw industry. As an important immunoregulatory factor, TGF-β1 plays a vital role in viral immune response. In order to study its role in the process of iridovirus infection, we have cloned this gene and studied its spatiotemporal expression patterns. The total length of TGF-β1 gene is 3157 bp, including 5′-untranslated region (UTR) of 712 bp, 3′-UTR of 1278 bp. The open reading frame length is 1167 bp that encodes 388 amino acids, including 6 exons and 5 introns. Homologous alignment showed that the amino acid sequence of TGF-β1 in spotted knifejaw had a close identity to Cynoglossus semilaevis, of about 76.67%. TGF-β1 is widely distributed in tissues, and high expressed in the head kidney, intestine, liver, skin, but shows a relatively low expression in the spleen and kidney. To further illustrate the expression patterns of TGF-β1 during viral infection, we have analyzed the expression patterns of TGF-β1 in the spleen, liver, kidney, and head kidney at different time points after iridovirus infection. In head kidney, spleen and liver, the expression of TGF-β1 was increased post infection. The peak level in the spleen and liver appeared 4 days post infection (dpi), and in the head kidney the peak appeared at 10 dpi. In the kidney, viral infection seemed to downregulate TGF-β1 expression. The highest expression was observed at day 0, then decreased at 4 dpi and reach the lowest level at 7 dpi. At 10 dpi, the expression had recovered but still lower than level of day 0. These results suggest that TGF-β1 could respond to iridovirus infection and may play an important role in the process of viral immunity. However, the different expression pattern of TGF-β1 in different tissues after viral infection requires further study.
