Defective chromatin structure in somatic cell cloned mouse embryos

Area of Science:

• Epigenetics
• Developmental Biology
• Reproductive Science

Background:

• Somatic cell nuclear transfer (SCNT) cloning often results in abnormal embryonic development due to failed epigenetic reprogramming.
• Trimethylation of histone H3 at lysine 27 (H3K27me3) is crucial for maintaining embryonic stem cell pluripotency by repressing differentiation genes.

Purpose of the Study:

• To investigate differential H3K27me3 modification patterns between normal and cloned blastocysts.
• To determine the relationship between H3K27me3 levels, gene expression, and the expression of Polycomb Repressive Complex 2 (PRC2) components in cloned embryos.

Main Methods:

• Comparative analysis of H3K27me3 modification in the inner cell mass (ICM) of normal and SCNT cloned blastocysts.
• Quantitative assessment of differentiation-related gene expression in normal versus cloned embryos.
• Analysis of the expression levels of PRC2 component genes (Eed, Ezh2, Suz12) in cloned and normal embryos.

Main Results:

• H3K27me3 modification was present in the ICM of normal blastocysts but absent in cloned blastocysts.
• Differentiation-related genes, normally marked by H3K27me3, showed significantly higher expression in cloned embryos.
• Expression of PRC2 component genes (Eed, Ezh2, Suz12) was significantly lower in cloned embryos compared to normal embryos.

Conclusions:

• Reduced expression of PRC2 components in cloned embryos leads to defective H3K27me3 modification.
• This epigenetic defect causes premature expression of developmental genes, leading to cloned embryo death.
• H3K27me3 modification status may serve as a critical epigenetic marker for assessing the developmental potential of cloned embryos.