Yolk protein in leech

Abstract

Tlzeromyzon tessulatum vitellin was identified as a lipoglycoprotein of 490 kDa. The insolubility of this molecule in low-ionic-strength media was used to extract it from the ovaries. Antiserum prepared against vitellin was shown to react with a coelomic fluid component of 520 kDa. This vitellin precursor, or vitellogenin, was purified by gel permeation and ion-exchange column chromatography. These two lipoglycoproteins were characterized by amino acid, carbohydrate and lipid analysis and subunit composition. In spite of differences in terms of native molecular mass, solubility and isoelectric point, the lipoglycoproteins isolated from the coelomic fluid and the ovary were similar in their subunit components (a single polypeptide of 165 kDa) and in their amino acid and carbohydrate compositions. However, vitellogenin was found to be more highly lipidated (31.8% by mass) than vitellin (24% by mass) and lipid analysis indicated a higher amount of sterols and phospholipids in vitellogenin. From these data, we conclude that vitellogenin and vitellin are probably dimers of two identical subunit polypeptides plus lipid and that, after vitellogenin is sequestered in the oocyte, part of its lipid component is stripped from the molecule to give vitellin. Furthermore, electrophoretic analysis seems to indicate that vitellogenin synthesis and secretion is initiated following the third and last blood meal of the animal but that vitellogenin significantly accumulates in the coelomic fluid before being incorporated in the oocytes suggesting a complex mode of vitellogenesis regulation.The production of egg yolk involves a massive synthesis of specific proteins which is under hormonal control. These proteins, termed vitellogenins, are generally synthesized externally to the site of accumulation. Depending upon the species, vitellogenins are secreted in the bloodstream or in the hemolymph, taken up by the developing oocytes and deposited as vitellins, the major yolk proteins [l, 21. Thus, in addition to its physiological importance for reproduction, vitellogenesis also provides a good system for the study of molecular mechanisms and hormonal regulation of egg maturation.Yolk proteins have been extensively investigated in oviparous vertebrates [I] and in insects [3, 41. In annelids, oocyte vitellin has been purified from nereid polychaetes [5, 61 and it has been shown that oocyte differentiation depends upon the incorporation of vitellogenin [7, 81. On the other hand, little is known for the two groups of clitellates: oligochaetes [9, 101 and hirudinae [I I]. In clitellates, eggs are generally of a small size and laid within a cocoon secreted by the clitellum and abundantly provided with reserve substances from which the embryo will develop, therefore making an accumulation of

Receptor-Ligand Interaction between Vitellogenin Receptor (VtgR) and Vitellogenin (Vtg), Implications on Low Density Lipoprotein Receptor and Apolipoprotein B/E

“…In nature, Vtg exists as a dimer containing symmetric binding sites (40). In our study, the receptor-binding site was found to be located in the VtgSE region.…”

Extensive Sequence Conservation Among Insect, Nematode, and Vertebrate Vitellogenins Reveals Ancient Common Ancestry

“…It will be interesting to compare the serine content of Vgs from other blood/protein-feeding insects and arthropods without silk glands. Amino acid composition studies indicate that the serine content of shrimp (Crustacea) (Tom et al 1992) and leech (Annelida) (Baert et al 1991) yolk proteins is no greater than that of the average eukaryotic protein (Doolittle 1986), or of nematode Vg5 (Spieth et al 1985) and boll weevil Vg (Trewitt et al 1992) which lack polyserine domains.…”

Oogenesis in four species of Piscicola (Hirudinea, Rhynchobdellida)

“…Moreover, only glossiphoniid leeches produce many large yolky eggs (Baert et al, 1991;Fernán-dez et al, 1992); leeches in the remaining families lay small yolk-poor eggs, which give rise to albuminotrophic cryptolarvae (Fernández et al, 1992).…”