The egg-jelly macromolecule, a fucose sulphate glycoconjugate, originates from the accessory cells of the ovary in the sea urchin Hemicentrotus pulcherrimus

Histological study on maturation, fertilization and the state of gonadal region following spawning in the model sea anemone, Nematostella vectensis

The starlet sea-anemone Nematostella vectensis has emerged as a model organism in developmental biology. Still, our understanding of various biological features, including reproductive biology of this model species are in its infancy. Consequently, through histological sections, we study here key stages of the oogenesis (oocyte maturation/fertilization), as the state of the gonad region immediately after natural spawning. Germ cells develop in a secluded mesenterial gastrodermal zone, where the developing oocytes are surrounded by mucoid glandular cells and trophocytes (accessory cells). During vitellogenesis, the germinal vesicle in oocytes migrates towards the animal pole and the large polarized oocytes begin to mature, characterized by karyosphere formation. Then, the karyosphere breaks down, the chromosomes form the metaphase plate I and the eggs are extruded from the animal enclosed in a sticky, jelly-like mucoid mass, along with numerous nematosomes. Fertilization occurs externally at metaphase II via swimming sperm extruded by males during natural spawning. The polar bodies are ejected from the eggs and are situated within a narrow space between the egg's vitelline membrane and the adjacent edge of the jelly coat. The cortical reaction occurs only at the polar bodies' ejection site. Several spermatozoa can penetrate the same egg. Fertilization is accompanied by a strong ooplasmatic segregation. Immediately after spawning, the gonad region holds many previtellogenic and vitellogenic oocytes, though no oocytes with karyosphere. Above are the first histological descriptions for egg maturation, meiotic chromosome's status at fertilization, fertilization and the gonadal region's state following spawning, also documenting for the first time the ejection of the polar body.

Primary structure of a 120 kDa protein associated with the fucose sulfate glycoconjugate constituting the acrosome reaction-inducing substance of the sea urchin, Hemicentrotus pulcherrimus

A fucose sulfate glycoconjugate (FSG), a natural acrosome reaction-inducer, was purified from the egg jelly of the sea urchin Hemicentrotus pulcherrimus. The FSG is composed primarily of four constituents: a 120 kDa protein, a 237 kDa protein, a 258 kDa protein, and a polysaccharide-containing protein. Among them, the 120 kDa protein was thought to play a critical role in the association of other FSG constituent proteins, and therefore was characterized from a structural point of view. The protein was isolated from the carboxymethylated FSG by preparative sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) under reducing conditions, and then digested with trypsin to obtain information regarding the primary structure. Based on the partial amino acid sequences of three internal peptides (FSG120KA: LHNNEYGYGDTAAGEPELAQEEID, FSG 120KG: AIDIPAETGHYGR, and FSG120KC: RPTFDLADAVDT) and the N-terminal peptide (LHNNEYGYGDTAAGEPELAQQEID) of the 120 kDa protein obtained from intact FSG, degenerate oligonucleotide primers were synthesized and used to amplify a 297 bp cDNA fragment. This fragment enabled us to obtain the full-length cDNA (3176 bp) by 5'- and 3'-rapid amplification of cDNA ends. The deduced amino acid sequence revealed that the 120 kDa protein is composed of 663 amino acid residues including 72 cysteine residues, and hence, about 40% is presumed to be carbohydrate by weight. The 120 kDa protein plays an important role in the association of FSG constituent proteins (258 and 237 kDa) through disulfide bonds.

Structure, function and biosynthesis of sperm-activating peptides and fucose sulfate glycoconjugate in the extracellular coat of sea urchin eggs

A decapeptide (GFDLNGGGVG) isolated from the solubilized jelly layer of the sea urchin Hemicentrotus pulcherrimus stimulates the respiration and motility of H. pulcherrimus spermatozoa and, in addition, produces a number of biological effects on H. pulcherrimus spermatozoa including increases in cAMP and cGMP levels, activation of a Na+/H+ exchange system, and increases in intracellular pH (pHi) and [Ca2+] ([Ca2+]i). The peptide activates the metabolism of endogenous phosphatidylcholine and promotes the acrosome reaction as a specific co-factor of a major acrosome reaction-inducing substance, fucose sulfate glycoconjugate. The peptide also induces an electrophoretic mobility change in the guanylate cyclase of the sperm plasma membrane with concomitant dephosphorylation and inactivation of the enzyme. Seventy-four peptides producing similar biological effects, named sperm-activating peptide (SAP), have since been purified from the solubilized jelly layer of seventeen species of sea urchins distributed over five taxonomic orders. These peptides show essentially the same biological effects on sea urchin spermatozoa although their activity and structures are specific at the ordinal level. Equilibrium binding experiments using a radioiodinated SAP-I analogue [GGGY(125I)GFDLNGGGVG] to H. pulcherrimus spermatozoa suggests the presence of two classes of receptors (high affinity and low affinity) specific for SAP-I binding. Based on the Kd values and EC50's for SAP-I's biological activity, we presume that the high affinity receptor is associated with respiration-stimulating activity and elevations in pHi, while the low affinity receptor is coupled to elevations in cGMP and [Ca2+]i. The radioiodinated SAP-I analogue crosslinks to a 71 kDa protein which contains a single membrane-spanning domain at almost near C-terminus. A SAP-I precursor which is synthesized in the accessory cells contains five SAP-I and seven SAP-I-like decapeptides, each separated by a single lysine residue.