PARENT SESSION
Spermatogenesis

THE MAMMALIAN MALE GERM CELL SPECIFIC SULFOGALACTOSYLGLYCEROLIPID IMPARTS RIGIDITY TO RAM TESTIS PHOSPHOLIPID BILAYERS.

Bou Khalil, Maroun^{1, 2}, Carmona, Euridice², Carrier, Danielle¹, Kates, Morris¹, Tanphaichitr, Nongnuj^{1, 2, 3}, ^{1 2 3}

ABSTRACT- The biophysical properties of ram testis lipids were investigated by Fourier transform infrared spectroscopy (FTIR) to provide a better understanding of the roles of the male germ cell specific sulfogalactosylglycerolipid (SGG) and polyunsaturated fatty acids (PUFAs)-containing phospholipids in the mammalian testicular germ cell. The composition of ram testes was dominated by phosphatidylcholine (PC) (30%) followed by phosphatidylethanolamine (PE) (20%), with sphingomyelin ranked next in distribution (10%). PC and PE possessed high levels of MUFAs and PUFAs (40-45 mol%), as detected by gas liquid chromatography. These testicular phospholipids did not display a phase transition in the temperature range 5-65^oC, corroborating the previous description of PUFAs' role in enhancing membrane fluidity. In contrast, sphingomyelin exhibited a relatively broad gel to liquid-crystalline phase transition with a peak near 35^oC, corresponding to its high content of saturated fatty acids (75 mol%). Interestingly, testicular total phospholipid bilayers exhibited a single T_m at 20^oC, indicating that the individual phospholipids did not segregate in the bilayer matrix, and that the observed T_m may be attributed to the higher rigidity of sphingomyelin. To assess the membranotropic properties of SGG in a testicular lipid bilayer environment, mixed phospholipid:SGG bilayers were reconstituted. SGG increased the rigidity of the testicular phospholipid bilayers at 10 and 20 mol%, shifting the T_m to 26 and 29^oC, respectively. Furthermore, reconstituted phospholipids:cholesterol:SGG bilayers, with the molar ratio existing in ram testis (6.8:2.2:1, mol/mol), exhibited a phase behavior comparable to that of ram testis total lipids (26^oC). Sphingomyelin and SGG exerted a rigidifying/stabilizing role in PUFAs-containing testicular phospholipid bilayers. This work was funded by NSERC (183958), CIHR (MT10366) and OGSST.

KEY WORDS: Spermatogenesis, Sulfogalactosylglycerolipid, Testicular Phospholipids, Thermotropic FTIR