Implantation and decidualization in rodents

Abstract

This article reviews the main events of embryo-implantation and decidualization in rodents. In common laboratory rodents the embryo attaches to the uterine epithelial lining, usually on days 4 to 6 of pregnancy. A progressive degree of proximity between trophoblast and epithelium occurs until the epithelial cells undergo apoptosis and detach from the basement membrane. During the attachment stage, the spindle-shaped connective tissue cells that underlie the epithelium next to the embryos transform into polyhedral and closely packed decidual cells. Following the epithelial detachment and the breaching of the basement membrane the embryo is thus in direct contact with decidual cells. These cells accumulate organelles associated with synthesis of macro-molecules, intermediate filaments, and eventually lipid droplets and glycogen. Another remarkable feature of decidual cells is the establishment of gap and adherens intercellular junctions. Differentiation of fibroblasts into decidual cells advances antimesometrially and mesometrially, creating in the endometrium several regions of cells with different morphology. The whole phenomenon of decidualization which is normally triggered by the embryo can be artificially induced in pseudo-pregnant or hormonally-prepared animals with the use of diverse stimuli. The uterine epithelium is probably responsible for the transduction of the initial stimulus. Prostaglandins have been shown to be important in the induction of decidualization. More recently other substances such as leukotrienes, platelet-activating factor (PAF), and transforming growth factor (TGF) have been thought to play a role in induction. Much evidence points to prostaglandin production by the decidual cells. New proteins such as a luteotropic factor, desmin, and other molecules were shown to be produced after rat stromal cells undergo decidual transformation. The extracellular matrix of the mouse decidua contains very thick collagen fibrils. Mouse decidual cells are also very active in phagocytosing the thick fibrils, contributing to the remodeling and involution of the decidua that accompanies embryonic growth. Radioautographic data indicates that mouse decidual cells produce and secrete collagen and sulfated proteoglycans.

Variations of Serum Estradiol and Progesterone Levels during Consecutive Reproductive States in Mongolian Gerbils (Meriones unguiculatus)

“…Embryo implantation occurs from the night of day 6 through the morning of day 7 during gestation in Mongolian gerbils [5,18,33] and requires the joint action of E2 and P4. The decidualization, which also needs the actions of the E2 and P4 begins shortly after implantation, and the weight and size of the uterus subsequently increase [1]. In Mongolian gerbils, the maternal decidual reaction is at its height of development two days after implantation [5].…”

Inhibition of Stat3 activation in the endometrium prevents implantation: A nonsteroidal approach to contraception

“…Implantation begins with the apposition of trophoblast cells of the hatched blastocyst and the apical surface of the luminal epithelium (LE) of the endometrium. At the same time, stromal cells beneath the site of attachment proliferate and differentiate in the process of decidualization (2). This is essential to support subsequent development of the embryo and placenta.…”

Dual control of LIF expression and LIF receptor function regulate Stat3 activation at the onset of uterine receptivity and embryo implantation

“…The stromal cells underlying the epithelium and adjacent to the site of blastocyst attachment respond by proliferating and differentiating, a process referred to as decidualization. Decidualization serves to sustain the early postimplantation embryo and to restrict trophoblast invasion of the uterus (2).…”