Considering the method used in our original study [20] , the source of the proteins located in the light-density fractions could belong to more than one membrane. In addition to the aforementioned sperm compartments (e.g., head and tail), the subcellular structure of the sperm encompasses different membranes, including the plasma membrane, outer acrosomal and inner acrosomal membranes, and nuclear and mitochondrial membranes. Although results obtained from the proteomic analysis suggested the absence of mitochondria and nuclear membranes in the sperm light-density fractions, DRM proteins coming from the inner and outer acrosomal membranes were also found in these fractions. The results of this study are in agreement with this possibility and with the assorted origin of plasma membranes contributing to the light-density fractions. In the tail, localization of BSG, SLC2A3, and FLOT2 suggests that DRM can be found along the different sections comprising the sperm flagella. The results in this study provide some other insightful clues for the sperm head. IZUMO cannot be detected on live sperm and is only exposed when plasma membrane integrity is disrupted by freezing, permeabilization, or the acrosome reaction [50, 51] ; accordingly, it is hypothesized that this protein localizes to the inner acrosomal membrane. In this respect, the association of IZUMO with the light-density fraction provides evidence that the inner acrosomal membrane contributes to the total light buoyant DRM fractions. Even an ephemeral structure like the cytoplasmic droplet seems to preserve DRMs, as suggested by the highly restricted location of TEX101 in the light-density fractions and by the results of the immunofluorescence studies. These results confirm studies [37, 49] supporting the heterogeneity of DRMs with regard to their protein and lipid composition.