Project description:Fertilization transforms sperm and egg into a totipotent embryo but the underlying mechanisms are unknown. We here report that gene expression initiates during the gamete-to-embryo transition in mouse embryos. Meiotic exit induced by sperm entry enhances a transcriptionally-permissive epigenetic landscape. Time-course analysis of single embryos revealed a succession of genome-wide transcription 'ripples' initiating within 2 hours. Disrupting key pluripotency transcription factor levels prior to sperm entry had little immediate effect, indicating that different mechanisms engender pluripotent and totipotent states. These findings suggest that a hierarchical gene expression program characterizes the emergence of totipotency during the gamete-to-embryo transition, with broad mechanistic implications for the reprogramming of cellular potency.
Project description:Fertilization transforms sperm and egg into a totipotent embryo but the underlying mechanisms are unknown. We here report that gene expression initiates during the gamete-to-embryo transition in mouse embryos. Meiotic exit induced by sperm entry enhances a transcriptionally-permissive epigenetic landscape. Time-course analysis of single embryos revealed a succession of genome-wide transcription 'ripples' initiating within 2 hours. Disrupting key pluripotency transcription factor levels prior to sperm entry had little immediate effect, indicating that different mechanisms engender pluripotent and totipotent states. These findings suggest that a hierarchical gene expression program characterizes the emergence of totipotency during the gamete-to-embryo transition, with broad mechanistic implications for the reprogramming of cellular potency.
Project description:Chromosomes are not randomly packed and positioned into the nucleus but folded in higher-order chromatin structures with defined functions. However, the genome of a fertilized embryo undergoes a dramatic epigenetic reprogramming characterized by extensive chromatin relaxation and the lack of a defined three-dimensional structure. This reprogramming is followed by a slow genome refolding that gradually strengthens the chromatin architecture during preimplantation development. Interestingly, genome refolding during early development coincides with a progressive loss of developmental potential suggesting a link between chromatin organization and cell plasticity. In agreement, loss of chromatin architecture upon depletion of the insulator transcription factor CTCF in embryonic stem cells led to the upregulation of the transcriptional program found in totipotent cells of the embryo, those with the highest developmental potential. This essay will discuss the impact of genome folding in controlling the expression of transcriptional programs involved in early development and their plastic-associated features.