Telomere Elongation During Pre-Implantation Embryo Development

The primary mechanism of telomere elongation in mammals is reverse transcription by telomerase. An alternative (ALT) pathway elongates telomeres by homologous recombination in some cancer cells and during pre-implantation embryo development, when telomere length increases rapidly within a few cell cycles. The maternal and paternal telomeres in the zygote are genetically and epigenetically distinct, with differences in telomere length and in chromatin packaging. We discuss models for how these asymmetries may contribute to telomere regulation during the earliest embryonic cell cycles and suggest directions for future research.