Relationship between nuclear remodeling and development in nuclear transplant rabbit embryos

Area of Science:

• Reproductive biology
• Developmental biology
• Cell biology

Background:

• Nuclear remodeling is crucial for reprogramming donor nuclei in cloned embryos.
• Understanding nuclear remodeling in rabbit embryos is essential for improving cloning efficiency.

Purpose of the Study:

• To characterize nuclear remodeling in nuclear transplant rabbit embryos.
• To investigate the relationship between chromatin behavior and embryo development.
• To determine the impact of synchrony between fusion and activation on nuclear remodeling and development.

Main Methods:

• Nuclear transfer of donor nuclei from various rabbit embryo stages (cleavage, morula, blastocyst).
• Evaluation of nuclear remodeling, including premature chromosome condensation (PCC) and pronuclear (PN) formation.
• Assessment of embryo development to blastocysts.
• Comparison of nuclear remodeling and development in activated versus non-activated oocytes.

Main Results:

• Development to blastocysts was similar for 8- and 32-cell donor nuclei but reduced for inner cell mass (ICM) and trophectoderm (TE) transplants.
• Premature chromosome condensation (PCC) occurred synchronously in all donor nuclei stages upon fusion into non-activated oocytes.
• Pronuclear (PN) formation was synchronous with female pronuclei for 8- and 32-cell transplants but delayed for ICM and TE transplants.
• Fusion into activated oocytes prevented PCC and extensive nuclear swelling, leading to reduced development.
• Nuclear remodeling, particularly PCC and swelling, is beneficial but not essential for blastocyst development.

Conclusions:

• Nuclear remodeling of donor nuclei is beneficial for, but not essential to, blastocyst development in rabbit embryos.
• Complete reprogramming appears to require nuclear remodeling events, such as PCC and subsequent swelling upon oocyte activation.