EXPRESSION OF THE STAR (STEROIDOGENIC ACUTE REGULATORY) PROTEIN IN TELEOST FISH

In vertebrates, the rate limiting step in steroidogenesis appears to be the movement of cholesterol across the mitochondrial membrane. In mammals this has been shown to be regulated by StAR; the Steroidogenic Acute Regulatory protein. The recent cloning of the fish homolog of StAR has provided the opportunity to study the role of this protein in steroidogenesis in fish. Based on sequence identity, it appears that StAR is well conserved within vertebrates and the initial characterization indicated that it is expressed in steroidogenic tissues including the ovaries, testes and head kidneys (Bauer et al., 2000; Kusakabe et al., 2002). However, more detailed investigations have now indicated some differences in the tissue expression of StAR in fish as compared to mammals. Methods Various tissues were obtained from sexually mature rainbow trout, brook trout, and zebrafish. The expression of StAR transcripts was investigated using Northern analysis and/or reverse transcriptase – polymerase chain reactions (RT-PCR). For brook trout and rainbow trout, Northern blots of mRNA were probed with the homologous trout StAR cDNA (BT-accession #AF232215; RT-accession #AB047032). For zebrafish and rainbow trout, complimentary DNA (cDNA) was prepared from tissue RNA and species-specific StAR primers were used for RT-PCR