Studies on the turtle tumor susceptibility gene TSG101: Full-length cDNA sequence, genomic structural analysis, and role in green turtle fibropapilloma

The tumor susceptibility gene TSG101 is a recently discovered gene whose fu nctional knockout in mouse fibroblasts leads to transformation and tumor fo rmation in nude mice. Human and mouse TSG101 cDNAs are 86% and 94% similar at the nucleotide and deduced amino acid levels, respectively. The highly c onserved protein sequences suggest that the mouse and human TSG101 are true gene homologs that share fundamental biological functions. Here, we report that the turtle TSG101 full-length cDNA sequence contained a 1,176-base-pa ir open translational reading frame predicted to encode a 392-amino-acid pr otein. Alignment of TSG101 sequences showed that the turtle cDNA sequence w as 82.3% and 84.4% similar to mouse and human TSG101 respectively, at the n ucleotide level and 89.3% and 91.9% similar to mouse and human TSG101 prote ins, respectively. A coiled-coil domain and a proline-rich region typical o f the activation domain of transcription factors were highly conserved amon g the turtle, mouse, and human TSG101. The leucine zipper motifs in the coi led-coil domains of turtle, mouse, and human TSG101 proteins were identical . Expression of TSG101 was observed in all turtle organs examined. The role of TSG101 in green turtle fibropapilloma (GTFP) was investigated by perfor ming reverse transcriptase-polymerase chain reaction (RT-PCR) on RNA derive d from various turtle tumor tissues and tumor cell lines. No transcript abn ormalities of turtle TSG101 were found in all examined GTFP samples (10 GTF P tumor tissues and 2 GTFP tumor cell lines) from RT-PCR products. Future s tudy will analyze the difference in turtle TSG101 expressions between GTFP and the corresponding normal tissue. In mammalian systems, TSG101 productio ns outside of a narrow range, either overexpression or deficiency, can lead to abnormal cell growth. It needs to be clarified whether turtle TSG101 in GTFP is up or down regulated.