Ultrastructural Characterization of Fresh and Vitrified In Vitro- and In Vivo-Produced Sheep Embryos

Area of Science:

• Embryology
• Reproductive Biology
• Cryobiology

Background:

• Cryopreservation of in vitro-produced (IVP) sheep embryos yields lower results compared to in vivo-derived embryos, limiting practical applications.
• Ultrastructural differences between IVP and in vivo-derived sheep embryos may explain variations in cryotolerance.

Purpose of the Study:

• To conduct the first ultrastructural evaluation of in vitro-produced (IVP) sheep blastocysts cryopreserved using open pulled straws (OPS).
• To compare the cryopreservation-induced ultrastructural damage in IVP blastocysts with that of in vivo-derived blastocysts.

Main Methods:

• Evaluation of four groups of sheep blastocysts: fresh IVP, fresh in vivo-derived, cryopreserved IVP (OPS), and cryopreserved in vivo-derived (OPS).
• Ultrastructural observation using semithin sectioning and scoring to assess cellular integrity and identify cryodamage.
• Analysis focused on microvilli, mitochondria, vesicles, cellular membranes, and overall intracellular preservation.

Main Results:

• Fresh IVP embryos exhibited fewer microvilli and mitochondria, suggesting metabolic deficiencies potentially impacting cryotolerance.
• Cryopreservation using OPS resulted in significant ultrastructural damage, particularly in IVP blastocysts (grade 3 scoring).
• Observed cryodamage included disrupted cellular membranes, loss of microvilli, and presence of cellular debris, with more severe effects in IVP embryos.

Conclusions:

• The ultrastructural integrity of IVP sheep blastocysts is compromised more severely by OPS cryopreservation compared to in vivo-derived embryos.
• Lower cryotolerance in IVP embryos may be linked to their lipid content and metabolic characteristics.
• Findings highlight the need for improved cryopreservation techniques for IVP sheep embryos to enhance their viability and utility.