Telomere regulation of mitochondria in porcine parthenogenetic embryos

Mitochondrial DNA copy number (mt-cn) and telomere length (TL) are considered secondary markers of embryonic quality. The present study investigated the relationship between mt-cn and TL in parthenogenetically activated porcine embryos. Oocytes collected from gilt ovaries were matured and subsequently activated. Presumptive zygotes were then cultured until blastocyst stage. In none treated embryos, the mt-cn increased consistently during embryonic development, whereas telomere elongation was observed between the oocyte and 4-cell stages. Mt-cn and TL showed significant correlations at both the 4-cell and blastocyst stages. In the second experiment, embryos were cultured in medium containing the telomerase inhibitor TMPyP4 or vehicle (water) until the blastocyst stage. TMPyP4 treatment shortened TL at both the 4-cell and blastocyst stages and reduced mt-cn in blastocysts. Immunostaining revealed that TMPyP4 treatment increased G-quadruplex (G4) expression at the 4-cell stage, increased p53 expression, and decreased the expression levels of PGC1 and TFAM at both 4-cell and blastocyst stage embryos. TMPyP4 treatment also increased mitochondrial membrane potential and ATP content in embryos. RNA-seq analysis of blastocysts indicated that mitochondria are a major target of TMPyP4 treatment. In addition, microinjection of a TERT plasmid elongated TL and increased mt-cn in blastocysts. In conclusion, these findings suggest that although TMPyP4 may directly affect mitochondrial function, TL plays a regulatory role in mitochondrial homeostasis during embryonic development.