Glycogen content of preimplantation mouse embryos

Protein Expression Landscape Defines the Formation Potential of Mouse Blastoids From EPSCs

Preimplantation embryo development is a precisely regulated process organized by maternally inherited and newly synthesized proteins. Recently, some studies have reported that blastocyst-like structures, named blastoids, can be generated from mouse ESCs (embryonic stem cells) or EPSCs (extended pluripotent stem cells). In this study, to explore the dynamic expression characteristics of proteins and their PTMs in mouse EPS blastoids, we revealed the protein expression profile of EPS blastoids and metabolite characteristics by TMT-based quantitative mass spectrometry (MS) strategy. Furthermore, the protein phosphorylation sites were identified to show the phosphoproteomic analysis in blastoids compared with mouse early embryos. Above all, our study revealed the protein expression profile of EPS blastoids compared with mouse embryos during preimplantation development and indicated that glucose metabolism is key to blastoid formation.

Glycogen in the uterus and fallopian tubes is an important source of glucose during early pregnancy†

Pregnancy loss is common during the peri-implantation period in mammals when glucose is required for both embryonic development and decidualization of the endometrium. As the uterus cannot synthesize glucose, all glucose must come directly from maternal circulation as needed or transiently stored as the macromolecule glycogen. Glycogen acts as a glucose reservoir, storing up to 55 000 glucose moieties per molecule. Endometrial glycogen concentrations are correlated with fertility in humans, indicating that glycogen is an essential source of glucose during early pregnancy. In humans and primates, endometrial glycogen concentrations peak during the luteal phase due to progesterone. In contrast, in rats and mink, estradiol triggers an accumulation of uterine glycogen during proestrus and estrus. In mated rats, the glycogen content of the endometrium increases again after implantation due to high levels of glycogen stored in the decidua. In mink, endometrial glycogen reserves are localized in the uterine epithelia at estrus. These reserves are mobilized before implantation, suggesting they are used to support embryonic growth. Uterine glycogen concentrations continue to decrease after implantation in mink, probably due to a lack of decidualization. How ovarian steroids stimulate glycogenesis in the endometrium is unclear, but current evidence suggests that estradiol/progesterone interacts with insulin or insulin-like growth factor signaling. In summary, endometrial glycogen is an essential source of glucose during the peri-implantation period. More work is needed to characterize differences among species, elucidate the fate of the glucose liberated from glycogen, and understand how ovarian steroids regulate glycogen metabolism in the uterus.

Submicroscopic localization of glycogen in mouse blastocysts developed in vivo and in blastocysts developed in vitro from two-cell embryos

Ultrahistochemical method according to Thiéry (1967) was used to determine the occurrence and localization of glycogen in blastocysts developed in vivo and in blastocysts developed from 2-cell embryos of the mouse for 62 to 64 h in in vitro culture. The presence of glycogen was found in blastocysts of both experimental groups. Glycogen had a monoparticulate character, i.e. the form of beta-granules, localized above all in the ground cytoplasm of cells. Their size varied from 10 to 30 nm. In the blastocysts developed in the physiological uterine environment the glycogen content was relatively low, trophoblasts cells containing regularly a higher amount of glycogen particles than embryoblast cells. In the blastocysts developed in the culture medium in the presence of currently used energy sources the distribution and content of glycogen were clearly graded according to the cell types. Compared with the in vivo-blastocysts, an abnormally high amount of glycogen was observed in the cytoplasm of trophoblast cells, a medium amount in the prospective endoderm cells and the minimum amount in the prospective ectoderm cells. The authors are of the opinion that differences in the accumulation of glycogen and its occurrence in the individual cells are in connection with their position in the blastocyst and with their relation to the surrounding microenvironment. It can be judged from the findings of glycogen deposits inside autophagic vacuoles and multivesicular bodies as well as inside extracellular located sacs that simultaneously with glycogen accumulation there also proceeds its partial degradation in lysosomal structures of blastocyst cells.

Comparison of polysaccharide synthesis between preimplantation stage mouse embryos and F9 embryonal carcinoma cells

Polysaccharide synthesis was compared between preimplantation stage mouse embryos and F9 embryonal carcinoma cells. When cells were labelled with [3H]fucose, elution profiles of the pronase digest from a Sephacryl S-200 column were similar for the two cell types and both had characteristic large polysaccharides of the same size (Mr 20-500K), although embryos contained less large polysaccharide than F9 cells, and embryonic polysaccharides were less acidic, suggesting poor sialosylation. A significant proportion of [3H]mannose was incorporated into complex-type glycopeptides in F9 cells, whereas in the case of embryonic cells most glycopeptides remained as high mannose-type. The most striking difference was observed when cells were labelled with galactose. In the case of embryonic cells, 90% of the radioactivity was incorporated into glycogen, whereas only 0.1% of the incorporated galactose occurred in this molecule in F9 cells. These observations indicate that carbohydrate metabolism of morula-stage embryos is very different from that of F9 cells.