Sperm Proteome Maturation in the Mouse Epididymis
November
Sperm Proteome Maturation in the Mouse Epididymis
Sheri Skerget 0 1 2
Matthew A. Rosenow 0 1 2
Konstantinos Petritis 0 1 2
Timothy L. Karr 0 1 2
0 Current address: Drosophila Genomics and Genetic Resources, Kyoto Institute of Technology , Saga Ippongi-cho, Ukyo-ku, Kyoto , Japan
1 1 Center for Infectious Diseases and Vaccinology, The Biodesign Institute, Arizona State University , Tempe , Arizona, United States of America, 2 Center for Proteomics, Translational Genomics Research Institute , Phoenix, Arizona , United States of America
2 Editor: Jay M. Baltz, Ottawa Hospital Research Institute and University of Ottawa , CANADA
In mammals, transit through the epididymis, which involves the acquisition, loss and modification of proteins, is required to confer motility and fertilization competency to sperm. The overall dynamics of maturation is poorly understood, and a systems level understanding of the complex maturation process will provide valuable new information about changes occurring during epididymal transport. We report the proteomes of sperm collected from the caput, corpus and cauda segments of the mouse epididymis, identifying 1536, 1720 and 1234 proteins respectively. This study identified 765 proteins that are present in sperm obtained from all three segments. We identified 1766 proteins that are potentially added (732) or removed (1034) from sperm during epididymal transit. Phenotypic analyses of the caput, corpus and cauda sperm proteomes identified 60 proteins that have known sperm phenotypes when mutated, or absent from sperm. Our analysis indicates that as much as one-third of proteins with known sperm phenotypes are added to sperm during epididymal transit. GO analyses revealed that cauda sperm are enriched for specific functions including sperm-egg recognition and motility, consistent with the observation that sperm acquire motility and fertilization competency during transit through the epididymis. In addition, GO analyses revealed that the immunity protein profile of sperm changes during sperm maturation. Finally, we identified components of the 26S proteasome, the immunoproteasome, and a proteasome activator in mature sperm.
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Competing Interests: The authors have declared
that no competing interests exist.
Advances in mass spectrometry and bioinformatics have greatly increased our understanding
of sperm composition and function. Sperm proteome data now exists for several mammalian
species, including the mouse, rat, human, macaque and bull [1–7]. While a better
understanding of the composition of mature sperm is emerging, our understanding of the complex
posttesticular sperm maturation process in mammals is considerably lacking. In this study, we use
proteomics to inform a systems-level understanding of the complex maturation process that
occurs in the mammalian epididymis.
In mammals, sperm mature and gain fertilization competency as they traverse a specialized
duct called the epididymis. This tissue can be generally separated into three distinct but
conserved morphological segments termed the caput (proximal), corpus (middle), and cauda
(distal) epididymis. When sperm leave the testis and enter the caput epididymis, they are
considered immature and are incapable of fertilization. During epididymal transit, sperm lose
or modify a number of their surface proteins and gain additional transient or permanent
surface proteins in a well-organized manner. To date, a small number of proteins including
CRISP1, ADAM7, GPX5 and SPAM1 have been identified as added to sperm during
epididymal transit [8–11].
Although it is well accepted that modification of sperm during epididymal transit ultimately
confers both motility and fertilization competency to sperm, the process remains poorly
understood [12]. One mechanism by which sperm are modified during epididmal transit is by
membranous vesicles called epididymosomes which are secreted by the epididymal epithelium
(reviewed in [13]). Epididymosomes collected from the epididymal lumen have been shown to
contain many proteins that have also been identified as components of sperm.
Epididymosomes are thought to interact with sperm during epididymal transit and play a role in
transferring proteins to sperm during epididymal transit [14]. The epididymis also contains a number
of distinct microenvironments that interact with sperm, although a detailed understanding of
the role of these microenvironments remains to be elucidated (reviewed in [15]).
Expressional profiling and principal component analysis identified 6 transcriptionally
distinct segments in the mouse epididymis [16]. However, because microarray data may not
necessarily directly reflect protein levels (reviewed in [17]), it is important to correlate
transcriptomic data with concomitant changes in sperm composition to provide a thorough
understanding of the sperm maturation process. An overall understanding of the process
would therefore benefit from a detailed analysis of these seg (...truncated)