52 Equine embryo size does matter!

The study investigated the link between the size of equine embryos and their gene expression. Small, medium and large embryos were compared, revealing differences in the types of genes expressed. Small embryos were found to express more genes related to mitochondria and apoptosis regulation, while large embryos expressed genes associated with faster growth and early pregnancy recognition signals.

Objective of the Research

• The study aimed to analyze gene expression in equine blastocysts (embryos) and to see if it varies based on the size of the embryo. The work revolved around examining the variation of gene expression in small, medium, and large equine embryos.

Methodology

• Saddlebred mares were inseminated at experimental farms after inducing ovulation. At 8 days post-ovulation, embryos from different dams were retrieved.
• The diameter of each embryo was measured and then bisected into pure trophectoderm (TE) and inner cell mass enriched (TE-ICM) trophoblast samples.
• DNA expression was analyzed in both sample parts of nine small (<700 µm), 11 medium (700–1200 µm), and eight large (>1200 µm) embryos.
• Paired-end, non-oriented RNA-sequencing was used for the testing, and differential expression was analyzed with the inclusion of farm and embryo sex as cofactors.

Findings

• In small embryos, higher expression of Insulin-like growth factor (IGF1) was observed in both ICM and TE compared to medium embryos.
• In large embryos, IGF1 was up-regulated in ICM and down-regulated in TE, both compared with medium embryos.
• Several P450 cytochromes like cytochrome P450 Aromatase and hydroxysteroid dehydrogenase were up-regulated in the ICM of large embryos compared to medium ones.
• Moreover, the Nanog Homeobox gene and several “SRY-Box” Transcription Factors, including SOX2, were down-regulated in the ICM of large embryos compared with medium embryos.

Conclusions

• The study concluded that the size of the equine embryo does impact the gene expression. Small embryos express more genes associated with mitochondria and apoptosis regulation.
• Large embryos, on the other hand, are involved in cell lineage development, rapid growth, and express genes involved in oestrogen production. These, in conjunction with IGF1, may contribute to the early signals for maternal recognition of pregnancy.