Co-localization and interaction at the molecular level of AKAP4 and QRICH2 in human sperm flagella. (A) AKAP4 and QRICH2 were observed co-localized in human sperm flagella by immunofluorescence staining (Red, AKAP4; Green, QRICH2; Blue, DAPI. Scale bars, 20 μm). (B) The interactions between AKAP4 and QRICH2 in human spermatozoa were detected by Co-IP in vivo. (C and D) The distribution of AKAP4 and QRICH2 by immunofluorescence staining in HEK-293T cells (Red, AKAP4; Green, QRICH2; Blue, DAPI).