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.
Project description:Totipotency is the ability of a single cell to give rise to all the differentiated cells that build the conceptus, yet how to capture this property in vitro remains incompletely understood. Defining totipotency relies upon a variety of assays of variable stringency. Here we describe criteria to define totipotency. We illustrate how distinct criteria of increasing stringency can be used to judge totipotency by evaluating candidate totipotent cell types in the mouse, including early blastomeres and expanded or extended pluripotent stem cells. Our data challenge the notion that expanded or extended pluripotent states harbor increased totipotent potential relative to conventional embryonic stem cells under in vivo conditions.
Project description:During early embryonic development, the transition from totipotency to pluripotency is a fundamental and critical process for proper development. However, the regulatory mechanisms governing this transition remain elusive. In this study, we conducted a comprehensive genome-wide CRISPR/Cas9 screen to investigate the 2-cell-like cells (2CLCs) phenotype in mouse embryonic stem cells (mESCs). This effort led to the identification of ten regulators that play a pivotal role in determining cell fate during this transition. Notably, our study revealed Mdm2 as a significant negative regulator of 2CLCs, as perturbation of Mdm2 resulted in a higher proportion of 2CLCs. Mdm2 appears to influence cell fate through its impact on cell cycle progression and H3K27me3 epigenetic modifications. In summary, the results of our CRISPR/Cas9 screen have uncovered several genes with distinct functions in regulating totipotency and pluripotency at various levels, offering a valuable resource for potential targets in future molecular studies.