Telomere length and telomerase activity in bovine pre-implantation embryos in vitro.

Telomeres are specialized structures that cap the ends of chromosomes and help to maintain genomic integrity and stability. Telomeres undergo dynamic changes during embryo development, which also represents an important stage for telomere elongation through telomerase enzyme activity. The objectives of this study were to examine changes in telomere length and telomerase activity from the early oocyte, through to the blastocysts stage of development, and the expression of factors with the potential to directly regulate telomeres. In vitro-produced bovine embryos were lysed and analysed for either relative telomere length, or telomerase activity using quantitative real-time PCR protocols. Our results reveal that relative telomere length is the shortest in the presumptive zygote stage of development and gradually increases to the blastocyst stage. We also demonstrate that differences between the mean telomere lengths throughout these stages are statistically significant (p < 0.05). Telomerase activity in the stages examined appears relatively constant until the blastocyst, where the highest level of activity is detected, leading to a significant difference in telomerase activity across embryonic stages (p < 0.005). Bovine telomerase RNA component (bTERC) expression levels were highest in the blastocyst, TERF1 transcripts showed little change in expression, and TERF2 expression decreased in the blastocysts (p < 0.05). Our results suggest that a complex integration of telomere-related RNA and proteins influences the regulatory mechanisms involved in 'reprogramming' of telomeres during early embryonic stages.