Implantation in the baboon: endometrial responses

Area of Science:

• Reproductive Biology
• Endocrinology
• Developmental Biology

Background:

• Blastocyst implantation in baboons occurs 8-10 days post-ovulation, involving distinct phases of endometrial changes.
• Estrogen and progesterone regulate initial uterine receptivity, influencing epithelial and stromal cell preparation.
• Embryonic signals play a critical role in modulating steroid-induced changes and establishing functional receptivity.

Purpose of the Study:

• To investigate the role of embryonic signals, specifically chorionic gonadotropin, in primate uterine receptivity.
• To delineate the cellular and molecular mechanisms underlying blastocyst implantation in baboons.
• To understand the interplay between maternal hormonal regulation and embryonic signaling in establishing a receptive endometrium.

Main Methods:

• Infusion of chorionic gonadotropin into non-pregnant baboons during the window of uterine receptivity.
• Analysis of changes in luminal and glandular epithelial cells, including endoreplication and glycodelin modification.
• Assessment of stromal fibroblast differentiation into decidual cells, characterized by actin filament and IGFBP-1 expression.

Main Results:

• Chorionic gonadotropin infusion induced epithelial changes, including endoreplication and altered glycodelin expression, mimicking fertile cycles.
• Stromal fibroblasts initiated differentiation towards a decidual phenotype, expressing actin filaments.
• While chorionic gonadotropin initiated stromal differentiation, complete decidualization was dependent on a signal from the conceptus.

Conclusions:

• Uterine receptivity in primates is a dynamic process influenced by both maternal hormones and embryonic signals.
• Chorionic gonadotropin can mimic some embryonic effects, preparing the endometrium for implantation.
• Full decidualization and successful implantation require a direct signal from the developing embryo.