Abstract
We investigated the identity and quantitative variations of proteins extracted from human sperm heads using a label-free Gel-MS approach. Sperm samples were obtained from three men with high sperm counts at three different time points. This design allowed us to analyse intra-individual and inter-individual variations of the human sperm head proteome. Each time point was analyzed in triplicate to minimize any background artifactual effects of the methodology on the variation analyses. Intra-individual analysis using the spectral counting method revealed that the expression levels of 90% of the common proteins identified in three samples collected at various time-points, separated by several months, had a coefficient of variation of less than 0.5 for each man. Across individuals, the expression level of more than 80% of the proteins had a CV under 0.7. Interestingly, 83 common proteins were found within the core proteome as defined by the intra- and inter-variation analyses set criteria (CV<0.7). Some of these uniformly expressed proteins were chaperones, peroxiredoxins, isomerases, and cytoskeletal proteins. Although there is a significant level of inter-individual variation in the protein profiles of human sperm heads even in a well-defined group of men with high sperm counts, the consistent expression levels of a wide range of proteins points to their essential role during spermatogenesis.
Highlights
The delivery of a genetically intact sperm nucleus during fertilization is required for normal embryo development
The application of this cut-off significantly reduced the median coefficient of variation (CV) of the total proteins analyzed from 0.3 to 0.1. This strategy ensured that the artefactual variation in proteins with low levels of detection among triplicates was minimized in the analysis
The methodology used in proteomics is suitable to the study of spermatozoa because these cells are transcriptionally silent, i.e., the nature of the protein profile reflects the functional status of sperm
Summary
The delivery of a genetically intact sperm nucleus during fertilization is required for normal embryo development. There is still little known about the functions of the NM or its protein components, there is a growing interest in studying the composition of the sperm NM as some nuclear proteins have been shown to have a role in normal sperm function [1,5,6,7,8,9]. The nuclear isoform of GPX4, nGPX4, has been implicated in matrix instability and in paternal DNA decondensation [11]. Taken together, these data strongly advocate for the importance of identifying the structural components of the NM and defining the functional roles of sperm nuclear proteins
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