TRANSCRIPTIONAL MODULATION OF APOPTOSIS REGULATORY PROTEIN SIVA1 UNDER DIFFERENT IMMUNE CHALLENGES IN RED LIP MULLET Liza haematocheila

Apoptosis, or programmed cell death is an obligatory event occur in the cell to keep the proper functions and cellular homeostasis of all multicellular organisms. Conversely deregulation of apoptosis could lead to a wide variety of severe pathological conditions. Siva 1 is a p53- inducible gene and the gene product is considered as an extensive inducer of apoptosis which can function both in extrinsic and intrinsic apoptotic pathways. Studies have shown that Siva 1 is overexpressed in various pathological conditions such as viral or bacterial infections and acute ischemic injury, hypoxia conditions and following DNA damage signals. Siva 1 binds with the CD27 molecule and interacts with the cell surface receptors GITR (glucocorticoid-induced tumour necrosis factor receptor) as well, to mediate the appropriate apoptotic signalling pathways where necessary.

Current study has focused on identifying a Siva 1 homolog from the Mullet cDNA library and relevant in-silico analysis of the protein was carried out using suitable bioinformatics software. Quantitative real-time PCR was used in determining the tissue specific mRNA expression of twelve different tissues collected from healthy red-lip mullets. Healthy fish were immune challenged individually with lipopolysaccharide (LPS), poly I:C, Lactococcus garvieae and Phosphate buffered saline (PBS/control) and selected tissues were collected in certain time intervals from five fish from each challenge. The collected tissues were pooled, cDNA was synthesized and applied in qPCR to determine the transcriptional modulation of the Siva 1 gene under different immune challenges.

Complete ORF of the Siva 1 of red lip mullet consisted of 867 base pairs encoding 168 amino acids with a predicted molecular weight of 18.5 kDa. The Siva superfamily domain has been conserved among the fish species. Brain tissue has the highest expression of Siva 1according to the tissue-specific expression analysis.  A significant up-regulation of the gene could be observed after 24 hours of immune challenge with LPS in both spleen and blood followed by a significant down-regulation in 48 and 72 hours. This may happen because of the activation of caspase dependent mitochondrial pathway of the apoptosis of the lymphoid cells due to the pathological condition. However profound investigations are necessary to clarify the exact mechanism of apoptosis facilitated by Siva 1.