How can sperm swim? The outer dense fiber of sperm tails 4 (gene: ODF4) is one of the proteins thought to be important for sperm tail movement that propels the sperm forward. Multiplex immunohistochemistry technique enabled us to examine the expression of this protein during sperm development (spermatogenesis) in more detail than ever before.

During the last phase of spermatogenesis, the round spermatids transform into mature sperm with unique morphological features and structures, such as an elongated tail (flagella) and acrosome, which are necessary for sperm motility and fertilization of the egg, respectively. This process is called spermiogenesis.

Outer dense fiber of sperm tails 4 (gene: ODF4) is one of the proteins thought to form the outer dense fibers, which are cytoskeletal structures found specifically in the sperm tail. Knowledge about its function in humans is mainly based on similarity to its mouse orthologue and human ODF4 is yet to be fully characterized. A mouse knock-out experiment showed that loss of ODF4 led to bent flagella that were unable to move normally and caused the sperm to swim backward (Ito et al 2023). Thus, ODF4 is probably also important for human sperm motility and male infertility.

To examine ODF4 protein expression during human spermiogenesis, ODF4 and five other proteins specific to different steps during the spermiogenesis were stained and visualized through fluorescently tagged antibodies using multiplex immunohistochemistry (mIHC/IF). The analysis shows that ODF4 (green) localizes to cells labeled as elongating (red) and elongated (white) spermatids - specifically in their cytoplasm and flagella. Thus, mIHC/IF provides more details about the ODF4 protein expression than conventional immunohistochemistry. More in-depth information about the mIHC/IF technique can be found here!