Epididymal Proteins Facilitate Sperm Maturation and Structural Stabilization

Fertilization is a decisive moment that enables the combination of two gametes to form a new organism; however, the decreasing fertilization rate has become a global issue and concern in the past decades. One of the research focuses of the Laboratory of Reproductive Physiology and Cell Biology, chaired by Assistant Prof. Pei-Shiue Tsai (蔡沛學) from the NTU School of Veterinary Medicine, is to understand the roles and functions of the reproductive tract in the process of sperm-egg binding and sperm maturation.

The research article published in the world-famous international journal, Biology of Reproduction, was conducted by second-year doctoral student Tse-En Wang (汪澤恩) on the topic of “The Involvement of Epididymal Proteins in the Maturation Processes of Sperm Cells.” The study was supported by the Young Investigator Merit Award of the Ministry of Science and Technology (MOST) and the Strategic Partnership Grants of the NTU Office of International Affairs (with the University of Tokyo). With these funds, Dr. Tsai’s lab was able to connect and integrate resources from different laboratories around the world (e.g., Dr. S.H. Li from the Mackay Memorial Hospital, Taiwan; Prof. K.-I. Meada, Associate Prof. F. Matsuda, and Dr. S. Minabe from the University of Tokyo, Japan; and Profs. B. Nixon and M. Dunn from the University of Newcastle, Australia) to perform large-scale proteomic screening, whole tissue imaging, epididymosome isolation, and glycan analyses for an in-depth study on the regulation and function of the epididymal secretory protein Quiescin Q6 Sulfhydryl Oxidase (QSOX).

In this study, we demonstrated for the first time that the two subtypes QSOX1 and QSOX2 are abundantly distributed in the male reproductive tract and display a complementary distribution throughout the epididymis. We further confirmed by the qualitative and quantitative measurement of the isolated epididymosome that QSOX2 is regulated by the apical blebbing secretion mechanism of the epididymal epithelial cells, and thereafter attached to the sperm head-neck junction after secretion to stabilize the structure of the spermatozoa. By contrast, the other subtype, QSOX1, is distributed in the lumen. The protein specifically adheres to the sperm cap region (acrosome) and inhibits the non-specific and immature acrosome reaction before the sperm encounters the egg. By using the Kisspeptin gene-knockout mice in combination with in vitro cell-based assays, we revealed that QSOX2 gene and protein expression is regulated by testosterone, likely via the atypical androgen receptors on the principal cells of epithelial cells. We also confirmed through the QSOX1-eGFP and QSOX2-eGFP systems established in this study that, unlike QSOX2 protein, the secretion of QSOX1 is not regulated by the reproductive hormones, but rather by the presence of sperm cells in the lumen. This major discovery overturns the traditional concept of unidirectional communication from the epithelial cells to the sperm in current textbooks, and shows the potential mechanism of bidirectional communication and interactions between the male reproductive tract and gametes. These research findings were not only published in the prestigious international journal, Biology of Reproduction, but also selected as the cover story in the November 2018 issue.

Reference:
Tse-En Wang; Sheng-Hsiang Li; Shiori Minabe; Amanda Anderson; Matt Dun; Kei-Ichiro Maeda; Fuko Matsuda; Hui-Wen Chang; Brett Nixon; Pei-Shiue Jason Tsai. “Mouse Quiescin Sulfhydryl Oxidases Exhibit Distinct Epididymal Luminal Distribution with Segment-Specific Sperm Surface Associations.” Biology of Reproduction, 99 (5): 1022-1033, Nov. 2018.

(Source: Dr. Pei-Shiue Tsai, NTU School of Veterinary Medicine)