Lipid dynamics in boar sperm studied by advanced fluorescence imaging techniques
The (re)organization of membrane components is of special importance to prepare mammalian sperm to fertilization. Establishing suitable methods to examine physico-chemical membrane parameters is of high interest. We characterized the behavior of fluorescent (NBD) analogs of sphingomyelin (SM), phosphatidylserine (PS), and cholesterol (Ch) in the acrosomal and postacrosomal macrodomain of boar sperm. Due to their specific transverse membrane distribution, a leaflet-specific investigation of membrane properties is possible. The behavior of lipid analogs in boar sperm was investigated by fluorescence lifetime imaging microscopy (FLIM), fluorescence recovery after photobleaching (FRAP), and fluorescence correlation spectroscopy (FCS). The results were compared with regard to the different temporal and spatial resolution of the methods. For the first time, fluorescence lifetimes of lipid analogs were determined in sperm cell membrane and found to be in a range characteristic for the liquid-disordered phase in artificial lipid membranes. FLIM analyses further indicate a more fluid microenvironment of NBD-Ch and NBD-PS in the postacrosomal compared to the acrosomal region. The concept of a more fluid cytoplasmic leaflet is supported by lower fluorescence lifetime and higher average D values (FCS) for NBD-PS in both head compartments. Whereas FLIM analyses did not indicate coexisting distinct liquid-ordered and -disordered domains in any of the head regions, comparisons between FRAP and FCS measurements suggest the incorporation of NBD-SM as well as NBD-PS in postacrosomal subpopulations with different diffusion velocity. The analog-specific results indicate that the lipid analogs used are suitable to report on the various physicochemical properties of different microenvironments.
KeywordsBoar sperm Acrosome Postacrosome Fluorescence lifetime imaging microscopy Fluorescence recovery after photobleaching Fluorescence correlation spectroscopy
This work was supported by the German Research Council (DFG MU1520/2-1) and by the German Ministry of Education and Research (BMBF Number 033 L046). The authors thank Andreas Herrmann and Thomas Korte (Humboldt-University Berlin) for helpful advice and discussion. The authors also appreciate the excellent technical assistance of Anita Retzlaff (Institute for Reproduction of Farm Animals Schönow e.V.) and Jenny Eichhorst (Leibniz Institute for Molecular Pharmacology).
- Adkins EM, Samuvel DJ, Fog JU, Eriksen J, Jayanthi LD, Vaegter CB, Ramamoorthy S, Gether U (2007) Membrane mobility and microdomain association of the dopamine transporter studied with fluorescence correlation spectroscopy and fluorescence recovery after photobleaching. Biochemistry 46:10484–10497CrossRefPubMedGoogle Scholar
- Bou Khalil M, Chakrabandhu K, Xu H, Weerachatyanukul W, Buhr M, Berger T, Carmona E, Vuong N, Kumarathasan P, Wong PT, Carrier D, Tanphaichitr N (2006) Sperm capacitation induces an increase in lipid rafts having zona pellucida binding ability and containing sulfogalactosylglycerolipid. Dev Biol 290:220–235CrossRefPubMedGoogle Scholar
- Haldar S, Chattopadhyay A (2013) Application of NBD-labeled lipids in membrane and cell biology. In: Mely Y, Duportail G (eds) Fluorescent methods to study biological membranes. Springer, Berlin, pp 37–50Google Scholar
- Müller P, Plazzo AP, Herrmann A (2011) Transbilayer movement and distribution of cholesterol. In: Devaux PF (ed) Membrane asymmetry and transmembrane motion of lipids. Wiley, Hoboken, pp 75–96Google Scholar
- Sezgin E, Levental I, Grzybek M, Schwarzmann G, Mueller V, Honigmann A, Belov VN, Eggeling C, Coskun U, Simons K, Schwille P (2012) Partitioning, diffusion, and ligand binding of raft lipid analogs in model and cellular plasma membranes. Biochim Biophys Acta 1818:1777–1784CrossRefPubMedGoogle Scholar
- Teichmann A, Gibert A, Lampe A, Grzesik P, Rutz C, Furkert J, Schmoranzer J, Krause G, Wiesner B, Schulein R (2014) The specific monomer/dimer equilibrium of the corticotropin-releasing factor receptor type 1 is established in the endoplasmic reticulum. J Biol Chem 289:24250–24262PubMedCentralCrossRefPubMedGoogle Scholar