Blastocyst Cell Number and Allocation Affect the Developmental Potential and Transcriptome of Bovine Somatic Cell...

Area of Science:

• Reproductive biology
• Developmental biology
• Genomics

Background:

• Somatic cell nuclear transfer (SCNT) is a key technology for cattle cloning but suffers from low efficiency.
• Most SCNT-derived embryos fail to develop into healthy calves despite in vitro development similar to fertilized embryos.

Purpose of the Study:

• To identify developmentally competent SCNT embryos based on blastocyst cell composition.
• To perform transcriptome analysis on single SCNT embryos to understand molecular differences related to developmental competence.

Main Methods:

• SCNT embryos expressing a nuclear-localized HcRed gene were analyzed for total cell and inner cell mass (ICM) counts using confocal microscopy.
• Embryos were individually transferred to recipient heifers, with pregnancy rates assessed by ultrasonography.
• Single-embryo RNA sequencing and weighted gene coexpression network analysis were performed.

Main Results:

• SCNT embryos that established pregnancy by day 35 had significantly fewer total cells (117 ± 6) compared to non-pregnant embryos (128 ± 5).
• A lower average ICM cell count (41 ± 3) was associated with successful pregnancies compared to higher counts (48 ± 2).
• Transcriptome analysis revealed gene expression clusters correlated with total cell and ICM cell numbers, enriched in processes like coenzyme metabolism and intracellular signaling.

Conclusions:

• SCNT embryos with reduced total cell and ICM numbers exhibit higher pregnancy establishment rates.
• These morphological differences are underpinned by distinct transcriptomic profiles in SCNT embryos.
• Identifying key molecular pathways can improve SCNT efficiency in cattle.