Insulin-like growth factor system components expressed at the conceptus-maternal interface during the establishment of equine pregnancy.
Authors: Gibson Charlotte, de Ruijter-Villani M, Stout Tom A E
Journal: Frontiers in veterinary science
Summary
# Editorial Summary The insulin-like growth factor (IGF) system—comprising IGF1 and IGF2, their receptors, and binding proteins—orchestrates embryo-maternal dialogue during early pregnancy in many species, yet its role in equine conceptus development remained poorly characterised. Gibson and colleagues examined mRNA and protein expression of IGF system components in endometrial and conceptus tissues collected on days 7, 14, 21 and 28 post-ovulation, alongside embryo transfer experiments using synchronous and asynchronous recipients, to map the temporal and spatial dynamics of this signalling system during the critical pre-implantation window. All major IGF components were present throughout early pregnancy, with endometrial IGF2, insulin receptor, and binding proteins showing progressive upregulation between days 7 and 28, whilst conceptus membrane expression of these factors increased proportionally with developmental advancement. Crucially, when embryos were transferred into asynchronous (day 3) rather than synchronous (day 8) recipients, IGF1, IGF2 and insulin receptor expression in the developing conceptus was significantly suppressed, whereas only insulin receptor expression changed in the out-of-phase endometrium—indicating the conceptus is acutely sensitive to uterine environment mismatch. These findings provide evidence that the IGF system mediates conceptus-maternal signalling during implantation preparation, with practical implications for understanding embryo transfer outcomes, pregnancy loss, and potentially for developing interventions to improve recipient mare synchronisation protocols and early pregnancy establishment rates.
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Practical Takeaways
- •Embryo transfer timing matters: asynchronous transfers (recipient uterus not synchronized with embryo stage) reduce growth factor signalling in the conceptus, which may explain reduced pregnancy success rates with mismatched timing
- •The IGF system appears critical for conceptus-maternal communication during early pregnancy establishment—understanding this mechanism could help optimize embryo transfer protocols and diagnose implantation failures
- •Future therapies targeting IGF system upregulation may improve pregnancy outcomes in mares with poor implantation responses or recurrent transfer failures
Key Findings
- •IGF system components (IGF1, IGF2, receptors, and binding proteins) are expressed in both endometrium and conceptus membranes during days 7-28 of equine pregnancy, with expression increasing with developmental stage
- •Endometrial IGF2, INSR, IGFBP1 and IGFBP2 expression significantly increased between days 7 and 28 of pregnancy
- •Asynchronous uterine environment (day 3 recipient for day 8 embryo) retarded IGF1, IGF2 and INSR expression in the conceptus, suggesting these factors mediate conceptus-maternal communication
- •IGF1R and IGF2 showed strong immunohistochemical expression in both endometrium and conceptus membranes, indicating active signalling pathways during implantation preparation