IDENTIFICATION OF A NOVEL GERM CELL-SPECIFIC mRNA-LIKE TRANSCRIPT (RtGST-1) PREDOMINANTLY EXPRESSED IN EARLY PREVITELLOGENIC OOCYTE IN RAINBOW TROUT (Oncorhynchus mykiss)

Abstract

Increasing evidences have shown that noncoding mRNA-like transcripts play important roles in a wide range of biological events such as cell differentiation and organogenesis. In this study, a novel germlinespecific transcript, termed RtGST-1, was identified by bioinformatics analysis of expressed sequence tags (ESTs) from a rainbow trout oocyte cDNA library. The novel transcript of 1146 bp has a polyadenylation signal and a poly (A) tail at the 3′ end but does not contain a significant open reading frame, suggesting that RtGST-1 is a noncoding mRNA-like transcript. Northern blot analysis detected a single form of ∼1.2 kb for the transcript in ovarian tissues. RT-PCR showed that the novel gene is specifically expressed in various stage ovaries as well as in immature testis, whereas no expression was detected in mature testis and somatic tissues. Quantitative real time RT-PCR analysis revealed that the expression of RtGST-1 is significantly high in early previtellogenic ovaries and early embryos of day 1 post fertilization. In situ hybridization analysis demonstrated that the novel transcript is localized exclusively in early previtellogenic oocytes and spermatocytes. These results indicate that the expression of RtGST-1 is developmentally regulated and it may play a crucial role in differentiation and/or development of germ cells and early embryos. The study represents the first report of a germline-specific mRNA-like transcript in fish, and provides a useful germ-cell marker for future studies on differentiation and/or development of germline cells in rainbow trout. (poster)