Chromosome stability differs in cloned mouse embryos and derivative ES cells

Area of Science:

• Reproductive biology
• Genetics
• Cell biology

Background:

• Somatic cell nuclear transfer (SCNT) challenges genome stability mechanisms during cell cycle progression within the ooplasm.
• Chromosomal spindle aberrations are observed in reconstructed oocytes shortly after transplantation, but their persistence into embryonic divisions is unclear.

Purpose of the Study:

• To analyze chromosomal spindles and karyotypes in cumulus cell-derived mouse clones during early mitoses.
• To investigate the persistence of chromosomal abnormalities and identify potential genetic or epigenetic factors contributing to cloning failure.

Main Methods:

• Analysis of chromosomal spindles and karyotypes in cloned mouse embryos derived from cumulus cells.
• Comparison of aneuploidy frequencies (trisomies, structural rearrangements) between cloned and fertilized embryos.
• Long-term observation of cloned mice for phenotypic mutations and inheritance patterns.

Main Results:

• Cloned embryos initially exhibit less aneuploidy than fertilized embryos, but this increases after ES cell derivation.
• A heritable phenotypic mutation, lacking a detectable karyotypic mark, was identified in a cloned mouse and its offspring.
• The study highlights both epigenetic contributions to cloning failure and the potential for undetected subchromosomal mutations.

Conclusions:

• Cloned embryo failure is largely attributed to epigenetic factors, but not all epigenetic conditions are reversible during gametogenesis.
• The cloning procedure is susceptible to pre-existing or induced subchromosomal mutations that escape cytogenetic detection.
• Genome stability in cloned embryos is compromised by factors beyond the scope of standard cytogenetic analysis, necessitating further investigation into subchromosomal alterations.