Nucleolar ultrastructure in bovine nuclear transfer embryos

Area of Science:

• Reproductive Biology
• Developmental Biology
• Cellular Reprogramming

Background:

• Nuclear transfer aims to reprogram donor nuclei to a zygotic state.
• Ribosomal RNA (rRNA) synthesis and nucleolus formation indicate successful reprogramming.
• Nucleolar ultrastructure changes reflect the initiation of rRNA synthesis.

Purpose of the Study:

• To examine nucleolar ultrastructure in bovine nuclear transfer embryos.
• To compare reprogramming efficiency based on cytoplast activation status.
• To correlate ultrastructural changes with RNA synthesis initiation.

Main Methods:

• Bovine embryos (in vitro produced and nuclear transfer) were analyzed.
• Nuclear transfer used MII (nonactivated) or S phase (activated) cytoplasts.
• Embryos were fixed at various time points post-fusion and developmental stages for ultrastructural analysis.

Main Results:

• Nonactivated cytoplasts led to nuclear envelope breakdown and abnormal nucleoli, with no embryos reaching the eight-cell stage.
• Activated cytoplasts resulted in intact nuclear envelopes and nucleolus remodeling.
• Nucleolus reorganisation and primary vacuole appearance occurred earlier in activated nuclear transfer embryos compared to controls.

Conclusions:

• Activated cytoplasts are essential for complete nucleolus remodeling and functional rRNA synthesis in bovine nuclear transfer embryos.
• Early nucleolar reorganisation in activated nuclear transfer embryos suggests successful reprogramming.
• Ultrastructural observations align with autoradiographic data on RNA synthesis initiation.