Fig. 1

Identification and characterization of ULF-EVs. A Transmission electron micrographs of ULF-EVs isolated from days 9, 12 and 15 of pregnancy and day 9 of estrus showed cup-shaped structures with a diameter of approximately 30–150 nm. The scale bar indicates 100 nm. B The particle size of ULF-EVs mainly concentrated around 100 nm, which was measured by NTA analysis. C Western blotting analysis revealed that ULF-EVs expressed specifical EVs markers CD9, CD63, and TSG101. However, calnexin was extremely enriched in the endometrium compared with corresponding ULF-EV samples. D–G PAS staining and quantitative analysis of representative uterine sections. As pregnancy progresses, LE or GE could secrete more ULF-EVs. Scale bars = 100 µm. The data are shown as mean ± SD and different lowercase letters correspond to significant differences at the p < 0.05 threshold