EXPRESSION OF NEW KDN-GANGLIOSIDES IN RAINBOW-TROUT TESTIS DURING SPERMATOGENESIS AND THEIR STRUCTURAL IDENTIFICATION

The developmental expression of 2-keto-3-deoxy-D-glycero- D-galacto-no nonic acid-containing glycosphingolipids (KDN-gangliosides) in rainbow trout testis during spermatogenesis was studied using a monoclonal an tibody, mAb.kdn3G, which recognizes the KDN alpha 2-->3Gal beta 1--> e pitope. A major KDN-ganglioside found in mature sperm, (KDN)GM3, KDN a lpha 2-->3Gal beta 1-->4Glc beta 1-->Cer (where Cer is ceramide), was expressed in testis throughout all stages of its maturation, On the co ntrary, four new KDN-gangliosides which were reactive with mAb.kdn3G w ere not detected in mature sperm, although they were identified in imm ature testis and expressed during spermatogenesis. The structures of t hese KDN-gangliosides were established by chemical, enzymatic and immu nochemical methods as: (i) (KDN)GD1a, KDN alpha 2-->3Gal beta 1-->3Gal -NAc beta 1-->4(KDN alpha 2-->3)Gal beta 1-->4Glc beta 1-->Cer; (ii) ( KDN, Neu5Ac)GD1a, KDN alpha 2-->3Gal beta 1-->3GalNAc beta 1-->4(Neu5- Ac alpha 2-->3)Gal beta 1-->4Glc beta 1-->Cer and Neu5Ac alpha 2-->3Ga l beta 1-->3GalNAc beta 1-->4(KDN alpha 2-->3)Gal beta 1-->4Glc beta 1 -->Cer; (iii) (KDN) GD1 alpha, KDN alpha 2-->3Gal beta 1-->3(KDN alpha 2-->6)GalNAc beta 1-->4Gal beta 1-->4Glc beta 1-->Cer; and (iv) (KDN, Neu5Ac)GD1 alpha, KDN alpha 2-->3Gal beta 1-->3(Neu5Ac alpha 2-->6)Gal NAc beta 1-->4Gal beta 1-->4Glc beta 1-->Cer. (KDN)GD1a and (KDN,Neu5A c)GD1a first appeared at an early stage of spermatogenesis, but (KDN)G D1 alpha and (KDN,Neu5Ac)GD1 alpha were not expressed until 2 months p rior to spermiation. While (KDN)GM3 was previously shown to contain on ly 4-sphingenine (d18:1) acylated with a C16:0 fatty acid, the new KDN -gangliosides discovered in this study were composed of 4-hydroxysphin ganine (t18:0) or 4-sphingenine (d18:1), and were acylated with a C24: 1 or C16:0 fatty acid, A possible function of these KDN-gangliosides i s suggested.