epigenetic programming in the zygotic pronuclei

Definition

Target type: biologicalprocess

The global programming of epigenetic modifications in the zygote following fertilization. The paternal genome undergoes active DNA demethylation before the first cell division, while the adjacent maternal genome is protected from this process. [GOC:sp, PMID:22868271]

Epigenetic programming in the zygotic pronuclei is a crucial process that establishes the foundation for development by reprogramming the parental genomes. It involves a series of intricate molecular events that re-establish totipotency, erase epigenetic marks inherited from the gametes, and lay the groundwork for lineage specification.

The process commences with the fusion of the sperm and egg, bringing together two haploid genomes. The pronuclei, the male and female nuclei within the fertilized egg, remain separate initially. During this period, active DNA replication occurs, and the parental genomes are prepared for the next crucial phase.

The primary focus of epigenetic programming is the erasure of pre-existing epigenetic marks. These marks, including DNA methylation and histone modifications, are inherited from the parental gametes and reflect their specific cellular identities. The erasure of these marks ensures a clean slate for embryonic development, allowing for totipotency and the potential to generate all cell types.

Several key enzymes and mechanisms are involved in epigenetic reprogramming. Ten-eleven translocation (TET) enzymes catalyze the oxidation of 5-methylcytosine (5mC) to 5-hydroxymethylcytosine (5hmC), which is an essential step in the demethylation process. Additionally, DNA methyltransferases (DNMTs) play a role in both establishing and erasing DNA methylation patterns.

Simultaneously with DNA methylation reprogramming, histone modifications also undergo substantial changes. Histone acetylation and methylation patterns are dynamically altered, contributing to the establishment of the appropriate chromatin structure and gene expression profile.

Furthermore, a unique class of non-coding RNAs, called piRNAs, play a crucial role in epigenetic programming. PiRNAs protect the integrity of the parental genomes from transposable elements, ensuring their proper silencing.

As the pronuclei migrate towards each other and fuse, the reprogramming process culminates in the formation of the zygotic nucleus. This nucleus now contains the complete diploid genome, which is poised for the first cell division and the initiation of embryogenesis.

The precise timing and sequence of these epigenetic events are tightly regulated, ensuring that the developing embryo acquires the necessary epigenetic landscape for proper development. The disruption of these processes can have profound consequences for embryonic development, leading to developmental abnormalities and disease.'
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Proteins (3)

Compounds (11)