Hematoxylin and eosin (H&E) staining was performed as previously described (15 (link),16 (link)). To deparaffinize the paraffin sections, slides were submerged for 5 min in a slide jar filled with xylene (Sinopharm Chemical Reagent Co., Ltd.), repeating this procedure twice and using fresh xylene each time. Subsequently, sections were rehydrated by running slides through a series of decreasing concentrations of EtOH (Sinopharm Chemical Reagent Co., Ltd.). Hematoxylin (Shanghai Jingke Chemical Technology Co., Ltd.) was used to stain the tissues for 5 min at room temperature, and after washing with tap water, differentiation in staining was visualized by submerging for 30 sec in 1% acetic acid. To visualize the blue staining, the sections were rinsed under running tap water for 5 min, after which the slices were dyed in eosin solution (Shanghai Jingke Chemical Technology Co., Ltd.) for 2 min at room temperature. After dehydration with EtOH and transparency with xylene, the slices were sealed with neutral balsam (G8590-100; Solarbio). Finally, tissues were imaged under an electron microscope (400x magnification; OLYMPUS CX-21; Shanghai Xinyu Biotechnology Co., Ltd.).