Understanding bovine embryo elongation: a transcriptomic study of trophoblastic vesicles

Area of Science:

• Reproductive biology
• Developmental biology
• Molecular genetics

Background:

• Embryonic development involves embryo and extra-embryonic tissue (EET) growth and differentiation for uterine implantation.
• Embryo elongation transforms the ovoid shape to tubular and then filamentous forms, regulated by gene expression.
• Developmental irregularities can alter gene expression during bovine embryo elongation.

Purpose of the Study:

• To investigate the molecular basis of elongation in bovine trophoblastic vesicles (TVs), which are EET pieces lacking an embryonic disc.
• To compare gene expression profiles of TVs with intact extra-embryonic tissues (EETs) during ovoid to filamentous stages.
• To understand the role of molecular signatures in TV elongation and differentiation.

Main Methods:

• Collected bovine conceptuses (D12-D18) and isolated pieces with/without embryonic discs (ED) for in vivo elongation assessment.
• Grew spherical blastocysts in vitro to D8 and applied similar treatments.
• Analyzed gene expression differences using a bovine array (10 K) and qPCR array (224 genes, 24 pathways).

Main Results:

• TVs exhibited variable elongation rates in vivo, sometimes resembling earlier-stage EET.
• Molecular signatures of TVs generally followed intact EET developmental trajectories (D12-D18).
• Distinct expression dynamics were observed between TVs and intact EET within each stage, with some similarities to other epithelial models.

Conclusions:

• Differences in TV and EET elongation stem from reduced TV length, signaling capacity, and altered uterine signaling.
• Modified crosstalk between conceptus and uterus influences elongation.
• Proper elongation requires close coordination between uterine, embryonic, and extra-embryonic tissues, with potential asynchronies in developmental cues.