Identification of N-acetylgalactosamine in carbohydrates of Xenopus laevis testis.

Identification of glycans in amphibian testis has shown the existence of N-acetylgalactosamine (GalNAc)-containing carbohydrates. Labeling of the sperm acrosome with GalNAc-binding lectins has allowed the identification of GalNAc-containing glycans in this organelle. Futhermore, this specific labeling of the acrosome has allowed the study of acrosomal biogenesis by lectin histochemistry. However, the testis of Xenopus laevis has never been analyzed by lectin histochemistry to locate GalNAc-containing glycoconjugates. The aim of this work was to elucidate the expression of GalNAc in glycoconjugates of Xenopus testis using five specific lectins. The results showed that most of the lectins labeled the interstitium with variable intensity. However, labeling of the different spermatogenetic germ cell types showed different labeling patterns. Some lectins produced weak or very weak staining in germ cells, for example, horse gram Dolichos biflorus agglutinin, which labeled most of the germ cell types, and lima bean Phaseolus lunatus agglutinin, which weakly labeled only spermatogonia, but did not stain other germ cells. By contrast, Maclura pomifera lectin (MPL) moderately labeled all germ cell types, except mature sperm. Labeling with other lectins was seen only at later stages, suggesting variations involved in the spermatogenetic development. Thus, snail Helix pomatia agglutinin labeled spermatids, but neither spermatogonia nor spermatocytes, while soybean Glycine max agglutinin (SBA) labeled from preleptotene spermatocytes to later stages. The periphery of the acrosome was labeled with MPL and SBA, but no specific labeling of the acrosomal content was seen with any lectin. Thus, the GalNAc-binding lectins that have been used as acrosomal markers in some amphibians cannot be used in Xenopus testis, suggesting that acrosomal glycoconjugates in amphibians are species specific.