Epigenetic regulation limits competence of pluripotent stem cell-derived oocytes.

Recent studies have reported the differentiation of pluripotent cells into oocytes in vitro. However, the developmental competence of in vitro-generated oocytes remains low. Here, we perform a comprehensive comparison of mouse germ cell development in vitro over all culture steps versus in vivo with the goal to understand mechanisms underlying poor oocyte quality.

Nucleosomes in mammalian sperm: conveying paternal epigenetic inheritance or subject to reprogramming between generations?

The genome of mammalian sperm is largely packaged by sperm-specific proteins termed protamines. The presence of some residual nucleosomes has, however, emerged as a potential source of paternal epigenetic inheritance between generations. Sperm nucleosomes bear important regulatory histone marks and locate at gene-regulatory regions, functional elements, and intergenic regions.

HP1 proteins regulate nucleolar structure and function by secluding pericentromeric constitutive heterochromatin.

Nucleoli are nuclear compartments regulating ribosome biogenesis and cell growth. In embryonic stem cells (ESCs), nucleoli containing transcriptionally active ribosomal genes are spatially separated from pericentromeric satellite repeat sequences packaged in largely repressed constitutive heterochromatin (PCH). To date, mechanisms underlying such nuclear partitioning and the physiological relevance thereof are unknown.

Mechanisms of maternal intergenerational epigenetic inheritance.

Mammalian embryos are formed by fusion of eggs and sperm. Here we provide an integrated overview of the major dynamic changes in transcriptional processes, chromatin composition and 3D organization which the maternal and paternal genomes undergo during oocyte and early embryonic development in mice. We derive mechanistic insights into molecular hierarchies and crosstalk between the various chromatin-associated processes that define three distinct types of maternal epigenetic memory states in oocytes to support pre-implantation and post-implantation development.

SUMOylated PRC1 controls histone H3.3 deposition and genome integrity of embryonic heterochromatin.

Chromatin integrity is essential for cellular homeostasis. Polycomb group proteins modulate chromatin states and transcriptionally repress developmental genes to maintain cell identity. They also repress repetitive sequences such as major satellites and constitute an alternative state of pericentromeric constitutive heterochromatin at paternal chromosomes (pat-PCH) in mouse pre-implantation embryos.

Primed Track, high-fidelity lineage tracing in mouse pre-implantation embryos using primed conversion of photoconvertible proteins.

Accurate lineage reconstruction of mammalian pre-implantation development is essential for inferring the earliest cell fate decisions. Lineage tracing using global fluorescence labeling techniques is complicated by increasing cell density and rapid embryo rotation, which hampers automatic alignment and accurate cell tracking of obtained four-dimensional imaging data sets. Here, we exploit the advantageous properties of primed convertible fluorescent proteins (pr-pcFPs) to simultaneously visualize the global green and the photoconverted red population in order to minimize tracking uncertainties over prolonged time windows.

Initiating meiosis in a dish.

Embryonic germ cells are formed from embryonic progenitors through a highly complex differentiation process, recapitulation of which has proved challenging. Two new studies in report culture conditions for embryonic stem cell‐derived primordial germ cell‐like cells (PGCLCs) that enable global DNA demethylation (Ohta , 2017), and subsequent initiation of meiosis (Miyauchi , 2017), allowing future manipulations to elucidate mechanisms driving germ line differentiation.