The egg jelly coat of sea urchins contains sulfated polysaccharide with an unusual structure, composed of linear chains of L-fucose or L-galactose, with well-defined repetitive units. The specific pattern of sulfation and the position of the glycosidic bond vary among sulfated fucans from different species of sea urchins. These polysaccharides show species specificity in inducing the acrosome reaction, which is a critical event for the fertilization. We already observed that spawned eggs from individual females of some species of sea urchins have one of two possible sulfated fucan isotypes. This polymorphism was observed in population from the Pacific but not from the Atlantic Ocean [1]. Females of the sea urchin L. variegatus, collected at Rio de Janeiro, spawn eggs containing a sulfated fucan with the following repeating units:[3-α-L-Fucp-2(OSO₃)-1à3-α-L-Fucp-4(OSO₃)-1à3-α-L-Fucp-2,4(OSO₃)-1à3-α-L-Fucp-2(OSO₃)-1]n, denominated as sulfated fucan I (SF I). Surprisingly, we observed that during the winter, a period of decrease fertility of the invertebrate, the females synthesis a different fucan, composed exclusively of 4-sulfated, 3-linked units, denominated as sulfated fucan II (SF II). Moreover, SF II has less potency to induction acrosome reaction when compared to SF I, the natural inductor. This result indicated a seasonal variation in the biosynthesis of sulfated fucan by the sea urchin L. variegatus. Possibly it involves an environmental regulation of the sulfotransferases expressed by the invertebrate. The seasonal variation in the biosynthesis of sulfated fucan may be related with a mechanism to regulated fertility of the invertebrate along the year.
[1]Vilela-Silva et al (2002) J. Biol. Chem, 277: 379-387
Financial support: CNPq, Faperj, IFS and CAPES.