Fig 1: BMP4 relieved age-related ER stress and promoted steroidogenesis in SWFs. The tissue sections of the D580-SWFs were labeled with fluorescence, ER stress marker GRP78 (green), and cysteine apoptosis factor caspase3 (red), which were coexpressed ((a) A–F) in the GCs of the follicle and slightly distributed in the TCs. BrdU-positive ((a) G–L) cells (red) were distributed in the GL of D580-SWFs after treatment with BMP4. Red: CYP11a1 and CYP19a1; green: BMPR1A; CYP11a1 and BMPR1A and CYP19a1 and BMPR1 were coexpressed ((b) A–L) in the GL of D580-SWFs (treated by BMP4 or GCs). Scale bar: 50 µm. Western blot and grey analysis ((c) A) of CYP11a1, CYP19a1, BCL2, CALR, CHOP, caspase3, caspase12, PERK, and GRP78. qRT-PCR analyzed ATF4, caspase3, and GRP78 mRNAs ((c) B) content in D580-SWFs with different treatment methods. Values were the mean ± SEM of three experiments. Different lowercase letters indicated significant difference (p < 0.05).