Horse conceptuses secrete insulin-like growth factor-binding protein 3

Area of Science:

• Reproductive Biology
• Developmental Biology
• Endocrinology

Background:

• Insulin-like growth factor-I (IGF-I) is crucial for early embryonic development across species.
• In rabbits, IGF-I binds to embryonic coats via insulin-like growth factor-binding protein 3 (IGFBP3).
• The role and origin of IGFBP3 in equine embryonic development were previously unclear.

Purpose of the Study:

• To investigate the presence and origin of IGF-I-binding activity and IGFBP3 in horse conceptuses.
• To determine if horse conceptuses secrete IGFBP3.
• To elucidate the role of conceptus-derived IGFBP3 in early equine embryonic development.

Main Methods:

• Ligand blot, Western blot, and Northern blot analyses were employed.
• Immunoprecipitation of radiolabeled proteins was performed on cultured conceptuses.
• Endometrial samples were also analyzed for IGFBP3 mRNA and protein.

Main Results:

• Horse conceptuses showed significant IGF-I-binding activity and immunoreactive IGFBP3, particularly within the conceptus capsule.
• Cultured horse conceptuses secreted IGFBP3 into the medium.
• While mare endometrium contained IGFBP3, minimal secretion into the uterine lumen was detected.

Conclusions:

• Horse conceptuses secrete substantial amounts of IGFBP3 into the conceptus capsule from Day 10 post-ovulation.
• The majority of IGFBP3 in the conceptus capsule is of embryonic origin.
• Conceptus-derived IGFBP3 likely enhances or modulates IGF action on the developing equine embryo.