Identification of zebrafish LPTS: a gene with similarities to human LPTS/PinX1 that inhibits telomerase activity.

Human LPTS/PinX1 is a newly identified telomerase inhibitory protein. Overexpression of the LPTS/PinX1 gene suppresses telomerase activity, results in shortened telomeres. To investigate the role of the LPTS gene in zebrafish, we cloned the homologous gene, zLPTS, which encodes a protein of 355 amino acids. Sequence analysis revealed that, like human LPTS/PinX1, the zLPTS protein has a conserved G-patch domain at its N-terminus and a lysine-rich domain at its C-terminus. Bioinformatics analysis showed the evolutionary conservation of zLPTS. Using RT-PCR and northern blot, we found that zLPTS was expressed in all zebrafish tissues with higher level in ovary, and in all embryonic developmental stages examined. Whole mount in situ hybridization revealed that zLPTS was expressed in all regions of early developmental embryos. The subcellular localization of zLPTS protein was showed in the nucleolus and telomeres. We also cloned the gene for zebrafish Telomerase Reverse Transcriptase (zTERT), a catalytic subunit of telomerase, and demonstrated that zLPTS protein can interact with zTERT through the TR-binding domain of zTERT. Further, we verified that zLPTS could inhibit telomerase activities in zebrafish embryos and human cancer cell line by TRAP assay. Our results clearly demonstrate that zLPTS is ubiquitously expressed in tissues and embryos and plays a function of inhibiting telomerase activity. This study may provide a useful system for further investigating the mechanism of telomere length regulation.