Aggregating embryonic but not somatic nuclear transfer embryos increases cloning efficiency in cattle

Area of Science:

• Reproductive Biology
• Developmental Biology
• Genetics

Background:

• Cloning efficiency in cattle remains a challenge, with significant differences observed between embryonic cell nuclear transfer (ECNT) and somatic cell nuclear transfer (SCNT).
• Embryo aggregation is a technique explored to potentially enhance developmental potential and cloning outcomes.

Purpose of the Study:

• To compare cellular and molecular effects of aggregating ECNT versus SCNT bovine embryos.
• To determine if embryo aggregation can improve cattle cloning efficiency and developmental rates.

Main Methods:

• Reconstructed cloned embryos using morula-derived blastomeres (ECNT) and various somatic cell lines (SCNT).
• Cultured embryos individually (1X) or as aggregates of three (3X), with in vitro-fertilized (IVF) embryos as controls.
• Assessed in vitro development, cell numbers (ICM, TC), ICM:TC ratios, and relative POU5F1 (OCT4) transcript levels.

Main Results:

• Aggregation compromised in vitro development of ECNT embryos but not SCNT or IVF embryos.
• Aggregates showed increased inner cell mass (ICM) and total cell (TC) numbers, but POU5F1 levels varied; ECNT and IVF aggregates maintained levels, while SCNT aggregates showed a decrease.
• ECNT aggregates demonstrated a significant increase in development to weaning (20% vs. 8% for 1X), while SCNT and IVF controls showed no improvement; high POU5F1 correlated with in vivo survival.

Conclusions:

• Striking biological differences exist between ECNT and SCNT embryos in response to aggregation.
• Aggregation enhances cloning efficiency and survival in ECNT but not SCNT cattle embryos.
• POU5F1 levels are a better indicator of in vivo survival potential than ICM:TC ratios in cloned bovine embryos.