Expression of two different sulfated fucans by females of Lytechinus variegatus may regulate the seasonal variation in the fertilization of the sea urchin

Abstract

The egg jellies of sea urchins contain sulfated polysaccharides with unusual structures, 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 polysaccharides from different species. These polysaccharides show species specificity in inducing the acrosome reaction, which is a critical event for fertilization. Females of the sea urchin Lytechinus variegatus spawn eggs containing a sulfated fucan with the repetitive sequence [3-alpha-L-Fucp-2(OSO(3))-1 --> 3-alpha-L-Fucp-4(OSO(3))-1 --> 3-alpha-L-Fucp-2,4(OSO(3))-1 --> 3-alpha-L-Fucp-2(OSO(3))-1](n). We now observe that, close to winter, a period of decreased fertility for the sea urchin, the females synthesize a distinct sulfated fucan with a simple structure, composed of 4-sulfated, 3-linked alpha-fucose residues. This sulfated fucan is inactive when tested in vitro for the acrosome reaction using homologous sperm. The amount of egg jellies spawned by females (and their constituent sulfated polysaccharides) varied greatly throughout the year. Apparently, there is a correlation between the temperature of the sea water and the expression of the 4-sulfated, 3-linked sulfated fucan. Overall, we described the occurrence of two isotypes of sulfated fucan in the egg jelly of the sea urchin L. variegatus, which differ in their biological activity and may be involved in the periodicity of the reproductive cycle of the invertebrate.

Sperm and Egg Jelly Coat from Sea Urchin Lytechinus variegatus Collected in Rio de Janeiro Contain Distinct Sialic Acid-Rich Polysaccharides

“…This conclusion was supported by the presence of polysaccharides composed by sulfated fucose units, as reported by previous studies (Vilela-Silva et al 2002;Cinelli et al 2007). Sulfated fucans and sialic acid-rich glycoconjugates are the only carbohydrate-rich molecules found around the egg jelly of sea urchins (Mikami-Takey et al 1991;Vilela-Silva et al 2008).…”

“…Mature specimens of the sea urchin L. variegatus were collected from the Guanabara Bay (Rio de Janeiro, Brazil) and given intracelomic injection of 0.5 M KCl (~2.0 mL per specimen) to obtain the gametes (Cinelli et al 2007). Eggs were recognized by an orange color and collected in a solution containing 450 mM NaCl, 9.0 mM KCl, 48 mM MgCl 2 , 10 mM CaCl 2 , and 6.0 mM NaHCO 3 (pH 8.0).…”

Drosophila sperm surface alpha-l-fucosidase interacts with the egg coats through its core fucose residues

“…5C, D). A similar effect with fucoidan and L-fucose was observed in several organisms, such as sea urchins (Cinelli et al, 2007), amphibians (Caputo et al, 2005), hamster (Moreno et al, 2001), rat (Shalgi et al, 1986), bovine (Tanghe et al, 2004), and human (Oehninger et al, 1992). In addition, when the enzyme was pre-incubated with Human IgG at concentration of 2 mg/ml or with bromelain at 1 mg/ml the binding was completely inhibited.…”

The structure of sulfated polysaccharides ensures a carbohydrate-based mechanism for species recognition during sea urchin fertilization

“…In contrast to the isoforms found in S. purpuratus and S. droebachiensis, those of L. variegatus differ dramatically in their capacity to induce AR in homologous sperm. Furthermore, in this species, expression of the fucan isotypes by females varies during different seasons of the year, and seems to be related to the periodicity of the reproductive cycle (Cinelli et al, 2007). The inactive isoform, which is composed of [3-α-L-Fuc-4(SO 4 )-1] units, is expressed mostly during periods of low reproduction.…”