Blastocyst-induced changes in the bovine endometrial transcriptome.

Area of Science:

• Reproductive Biology
• Embryology
• Genomics

Background:

• Understanding early embryo-maternal interactions is crucial for reproductive success.
• Endometrial receptivity is a key factor in establishing pregnancy.
• Blastocyst-stage embryos are known to influence the maternal environment.

Purpose of the Study:

• To determine if blastocyst co-culture induces detectable responses in endometrial explants.
• To investigate the requirement for direct embryo-endometrial contact in stimulating gene expression.
• To establish the blastocyst threshold for eliciting an endometrial response and its stage specificity.

Main Methods:

• Co-culture of bovine endometrial explants with varying numbers of Day 8 blastocysts for 6 or 24 hours.
• Analysis of gene expression, focusing on interferon-stimulated genes (ISGs) and other selected transcripts.
• Assessment of responses to blastocyst-conditioned medium and different embryonic stages (oocytes, 2-cell, morulae).

Main Results:

• Blastocyst co-culture induced upregulation of specific ISGs (MX1, MX2, OAS1, ISG15, RSAD2) in endometrial explants.
• A minimum of five blastocysts were required for a detectable ISG response, with maximal expression at 20 blastocysts.
• The response was specific to blastocysts; oocytes, 2-cell, or morula stages did not induce significant changes. Direct contact was not necessary, as conditioned medium alone stimulated ISG expression.

Conclusions:

• Bovine blastocysts can induce endometrial gene expression changes as early as Day 8 of gestation.
• Local embryo-maternal signaling occurs via soluble factors in blastocyst-conditioned medium.
• This study supports the concept of paracrine signaling mediating early pregnancy establishment in cattle.