161 MODULATION OF TELOMERASE ACTIVITY IN BOVINE EMBRYOS USING CYTOPLASMATIC PLASMID INJECTION

Abstract

Telomeres are repetitive, noncoding sequences at the ends of linear chromosomes that shorten with each cell division. They play an important role in aging and affect the regenerative capacity of cells. The holoenzyme telomerase rebuilds telomeres and is composed of 2 components, i.e. the catalytic protein component telomerase reverse transcriptase (TERT) and the telomerase RNA component (TERC). In mammals, telomerase is active during embryogenesis, in germ cells and a subset of stem and progenitor cells. In the present study, we set out to express the TERC component alone and then in combination with TERT, the human telomerase complex, in bovine embryos. The human telomerase components are highly homologous to bovine telomerase genes. Here, 3 different expression constructs encoding hTERC, hTERT, and a green fluorescent protein (GFP) reporter were co-injected into bovine zygotes cytoplasm, and three groups of 528, 1865, and 110 zygotes were constituted; hTERC/GFP (Group 1), hTERT/hTERC/GFP (Group 2), and GFP alone (Group 3), respectively. GFP fluorescence was used to identify successfully injected embryos. This method has recently been established in our laboratory. Injected and control embryos were cultured for 7 days to the blastocyst stage in vitro and the impact on early embryonic development and the physiological consequences of an ectopic overexpression of telomerase in early bovine embryos were assayed. We obtained 45 blastocysts with green fluorescence in the first, 192 in the second, and 28 in the third group. Embryos with GFP fluorescence were frozen for subsequent PCR analysis and telomerase activity measurement. Some blastocyts were analyzed using quantitative fluoresence in situ hybridization to monitor telomere length. Control groups were analyzed for the endogenous levels of TERC and TERT. Results indicate that endogenous TERC and TERT are up-regulated in morulae and blastocyts. In this study, we show that human TERC and TERT can be expressed in blastocysts by cytoplasmic plasmid injection in bovine zygotes. Statistical analyses were performed using the JMP 7.0.1 for Windows software (SAS Institute Inc., Cary, NC, USA). The Tukey-Kramer test was applied to compare the group means. The expression of hTERC alone resulted in a significant extension of telomere length of 280 telomere fluorescence units. Expression of both components also resulted in a significant extension of telomere length. In conclusion, TERC component alone is sufficient to elongate telomere length. The activity measurement showed that telomerase activity in the hTERT and hTERC injected group is 1.77 times higher than in the control group. Findings from this study will allow a comprehensive analysis of the functions of TERT and TERC in early embryogenesis. The ectopic expression of telomerase components in bovine embryos could pave new avenues for generating stem cells and for the development of novel regenerative therapies.

Funded by DFG.