Mol Hum Reprod 2018 Apr 01;244:185-202. doi: 10.1093/molehr/gax071.

Raman micro-spectroscopy analysis of different sperm regions: a species comparison.

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STUDY QUESTION: Is Raman micro-spectroscopy a valid approach to assess the biochemical hallmarks of sperm regions (head, midpiece and tail) in four different species? SUMMARY ANSWER: Non-invasive Raman micro-spectroscopy provides spectral patterns enabling the biochemical characterization of the three sperm regions in the four species, revealing however high similarities for each region among species. WHAT IS KNOWN ALREADY: Raman micro-spectroscopy has been described as an innovative method to assess sperm features having the potential to be used as a non-invasive selection tool. However, except for nuclear DNA, the identification and assignment of spectral bands in Raman-profiles to the different sperm regions is scarce and controversial. STUDY DESIGN SIZE, DURATION: Raman spectra from head, midpiece and tail of four different species were obtained. Sperm samples were collected and smeared on microscope slides. Air dried samples were subjected to Raman analysis using previously standardized procedures. PARTICIPANTS/MATERIALS, SETTING, METHODS: Sperm samples from (i) two donors attending the infertility clinic at the Centre of Reproductive Medicine and Andrology; (ii) two C57BL/6 -TgN (ACTbEGFP) 1Osb adult mice; (iii) two adult Cynomolgus monkeys (Macaca fascicularis) and (iv) two sea urchins (Arbacia punctulata) were used to characterize and compare their spectral profiles. Differences and similarities were confirmed by principal component analysis (PCA). MAIN RESULTS AND THE ROLE OF CHANCE: Several novel region-specific peaks were identified. The three regions could be differentiated by distinctive Raman patterns irrespective of the species. However, regardless of the specie, their main spectral pattern remains mostly unchanged. These results were corroborated by the PCA analysis and suggest that the basic constituents of spermatozoa are biochemically similar among species. LIMITATIONS REASONS FOR CAUTION: Further research should be performed in live sperm to validate the detected spectral bands and their use as markers of distinctive regions. WIDER IMPLICATIONS OF THE FINDINGS: Raman peaks that have never been described in the sperm cell were detected. Particularly important are those that are unique to the midpiece as they might be a reference to the identification of sperm mitochondria, whose function is highly correlated with that of sperm. In the future, Raman micro-spectroscopy has the potential to be applied in assessment of male fertility. LARGE SCALE DATA: N/A. STUDY FUNDING AND COMPETING INTEREST(S): This work was supported by BMBF project ''Sperm Ident'' (FKZ:13N13024) and the DAAD-CRUP bilateral exchange program (AI A06/16-57213087). S.A. is a recipient of a fellowship from the Portuguese foundation for science and technology (FCT-SFRH/BPD/110160/2015) and R.DC. is a recipient of a DAAD PhD stipend (91590556). There is no competing interest.

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Genes referenced: LOC100887844 LOC115919910 LOC115925415