Review: Implantation and placentation in ruminants

Area of Science:

• Reproductive Biology
• Mammalian Placentation
• Ruminant Ungulates

Background:

• Ruminants exhibit a unique epitheliochorial placenta during early pregnancy.
• Binucleate cells (BNCs) in the trophoblast are crucial for placental development and function.
• These BNCs fuse with the uterine epithelium, forming specialized structures in sheep and cattle.

Purpose of the Study:

• To review historical and current knowledge of ruminant conceptus implantation and placental development.
• To highlight the unique cellular and molecular aspects of the ruminant placenta.
• To emphasize the need for advanced techniques like single-cell analysis for deeper insights.

Main Methods:

• Review of existing literature on ruminant placentation.
• Focus on cellular dynamics, including binucleate cell migration and fusion.
• Discussion of gene expression in placenta-specific cells.

Main Results:

• Ruminant placentas transition from epitheliochorial to synepitheliochorial.
• Binucleate cells form placental cotyledons and express key pregnancy-associated genes.
• Placentomes, formed by cotyledon-caruncle interaction, are vital for fetal nutrition.

Conclusions:

• The ruminant placenta's unique structure, driven by binucleate cells, is essential for successful gestation.
• Single-cell analysis offers a promising avenue to understand cellular heterogeneity and placental function.
• Improved understanding of ruminant placental development is critical for addressing pregnancy loss and enhancing reproductive efficiency.