Epithelial autolysis during implantation of the mouse blastocyst: an ultrastructural study

Abstract

An ultrastructural investigation was made of cell death in the uterine epithelium during the implantation of the mouse blastocyst. Cell death occurs in two phases: (i) early individual cell death, and (ii) later general cell death. Individual dead epithelial cells are phagocytosed and digested by trophoblast cells. At 95 h post coitum (p.c.) there are 1–4 dead cells; at 105 h and 113 h, 6–8 dead cells, and at 116 h, 2–3 dead cells. No lysosomal involvement could be identified in the death of these cells. The general breakdown of the uterine epithelium around the implanting blastocyst is first recognizable at the ultrastructural level at 113 h p.c, and continues until the adjacent deteriorated epithelium has been phagocytosed by the trophoblast cells at 119 h p.c. Ultrastructurally, from 113 h p.c. cytoplasmic portions of epithelial cells are trapped within cytosegrosomes, and there is an increase in size of the dense lysosomal bodies found in viable epithelial cells at 105 h p.c. The dense bodies, which are positively stained for acid phosphatase enzyme at 105 h p.c, increase in diameter approximately 3–5 times between 105 h p.c. and 119 h p.c. These results provide evidence of intracellular digestion of small portions of the cytoplasm possibly through the formation of cytosegrosomes which then fuse with residual bodies already present. Thus the evidence favours a process of autolytic breakdown of the uterine epithelium around the implanting blastocyst.

Phagocytosis reveals a reversible differentiated state early in the development of the mouse embryo

“…As in the case of macrophages, phagocytosis could be part of an antimicrobial defense system. Other functions may include scavenging of dead cells and debris, possibly residual sperm cells (see Figure 2), but more likely trophectoderm cells engaged in programmed cell death (El‐Shershaby and Hinchcliffe, 1975; Coucouvanis and Martin, 1995; Rassoulzadegan et al ., 1998). Another likely function is a role in the invasion by the young parasite of the uterine wall.…”

Dynamic Changes of Gene Expression in Mouse Mural Trophectoderm Regulated by Cdx2 During Implantation

“…Since these processes are initiated from the mTE, the acquisition of adhesion and migration ability in the mTE is critical for the implantation progression ( Sutherland, 2003 ). Some characteristic changes of the mTE which allow it to adhere to and invade the endometrium have already been identified, such as the activation of integrin signaling, the phagocytosis-like mechanism and the vascular-like gene expression patterns ( El-Shershaby and Hinchliffe, 1975 ; Parr et al, 1987 ; Armant, 2005 ; Chaen et al, 2012 ; Li et al, 2015 ; Govindasamy et al, 2021 ). However, the overall picture and time-course of the characteristic changes of the mTE, and their regulatory mechanisms remain largely unclear.…”