Precursor-product relationship between chicken vitellogenin and the yolk proteins: the 40 kDa yolk plasma glycoprotein is derived from the C-terminal cysteine-rich domain of vitellogenin II

Vitellogenin-derived yolk proteins in a hybrid sturgeon, bester (Huso huso x Acipencer ruthenus): identification, characterization and course of proteolysis during embryogenesis

Vitellogenin (Vg) and its corresponding yolk protein (YP) products, YP1, YP2 and YP3, were isolated from serum of estrogen-treated hybrid sturgeon (bester; Huso huso X Acipencer ruthenus) and eggs from untreated fish, respectively. Vitellogenin had an apparent molecular mass of 580 kDa and appeared as two major bands corresponding to 180 kDa and 120 kDa after SDS-PAGE. Apparent molecular weights of YP1, YP2 and YP3 were 370 kDa, 88 kDa and 19 kDa, respectively. After SDS-PAGE, YP1 appeared as a main band of 110 kDa, while YP2 was resolved as a single band of 94 kDa and 29 kDa band under non-reducing and reducing conditions, respectively. Yolk protein 3 appeared as a diffuse band corresponding to 16 kDa and two faint bands below 14.4 kDa after SDS-PAGE. However, the 16 kDa band alone was observed after dephosphorylation with alkaline phosphatase. The course of cleavage of yolk proteins in bester embryos and alevins was observed by SDS-PAGE and Western blotting from fertilization onward. After hatching, the main 110 kDa band of YP1 was degraded into smaller peptides during development, while YP2 hardly showed any such structural changes. The amino acid compositions of purified yolk proteins indicated that YP1, YP2 and YP3 were bester lipovitellin, beta-component, and phosvitin, respectively.

Identification and characterization of proteases involved in specific proteolysis of vitellogenin and yolk proteins in salmonids

A pepstatin A-sensitive enzyme involved in yolk formation was purified from the masu salmon (Oncorhynchus masou) ovary using in vitro generation of yolk proteins from purified vitellogenin to assay enzymatic activity. Purification of the enzyme involved precipitation of ovarian extracts by water and ammonium sulfate followed by five steps of column chromatography. After SDS-PAGE and Western blotting, the purified enzyme appeared as a single approximately 42 kDa band that was immunoreactive to anti-human cathepsin D. The course of proteolytic cleavage of the three major yolk proteins (lipovitellin, beta'-component, and phosvitin) in fertilized masu salmon and Sakhalin taimen (Hucho perryi) eggs and embryos was visualized by SDS-PAGE and Western blotting using specific antisera. Major yolk protein bands appeared in positions corresponding to 92 kDa, 68 kDa, and 22 kDa (lipovitellin-derived peptides), as well as 17 kDa (beta'-component). During embryo development, the 92 kDa and 22 kDa bands gradually decreased in intensity, becoming undetectable in alevins. The 68 kDa band and a minor 24 kDa band became more intense after the eyed stage. Two additional peptides, corresponding to 40 and 28 kDa, newly appeared in alevins. During embryonic growth, the beta'-component band (17 kDa) persisted and phosvitin appeared to be progressively dephosphorylated. In vitro analysis of lipovitellin proteolysis indicated that the enzyme involved is a Pefabloc SC-sensitive serine protease. These results demonstrate, for the first time, that a cathepsin D-like protease and serine proteases play key roles in yolk formation and degradation, respectively, in salmonid fishes.

Subunit composition of the zinc proteins alpha- and beta-lipovitellin from chicken

Chicken alpha- and beta-lipovitellin are derived from parent vitellogenin proteins and contain four subunits (125, 80, 40, and 30 kDa) and two subunits (125 and 30 kDa), respectively. Metal analyses demonstrate both are zinc proteins containing 2.1 +/- 0.2 mol of zinc/275 kDa per alpha-lipovitellin and 1.4 +/- 0.2 mol of zinc/155 kDa per beta-lipovitellin, respectively. The subunits of beta-lipovitellin, Lv 1 (MW 125 kDa) and Lv 2 (MW 30 kDa), are separated by gel exclusion chromatography in the presence of zwittergent 3-16. Zinc elutes with Lv 1, suggesting that this subunit binds zinc in the absence of Lv 2. The subunits of alpha- and beta-lipovitellin were separated by SDS-PAGE, digested with trypsin, and mapped by reverse-phase HPLC. The peptide maps of the 125-kDa subunits from alpha- and beta-lipovitellin are essentially identical. Similar results are obtained for the 30-kDa subunits of both lipovitellins. The sequences of five and four peptides of the 125-kDa subunit of alpha- and beta-Lv, respectively, and two peptides of the 30-kDa subunit of alpha- and beta-lipovitellin were determined and match those predicted from the gene for vitellogenin II, Vtg II. Comparison of the amino acid composition of the 125- and 30-kDa subunits of alpha- and beta-lipovitellin support the conclusion that they originate from the same gene. The sequences of peptides from the 80- and 40-kDa subunits of alpha-lipovitellin have not been found in the NCBI nonredundant data bank. The 27-amino acid N-terminal sequence of the 40-kDa protein is 56% similar to the last third of the Lv 1-coding region of the Vtg II gene, suggesting it may come from an analogous region of the Vtg I gene. We propose a scheme for the precursor-product relationship of Vtg I.

Two forms of vitellogenin, yielding two distinct lipovitellins, play different roles during oocyte maturation and early development of barfin flounder, Verasper moseri, a marine teleost that spawns pelagic eggs

Two forms of vitellogenin (Vg), Vg A and Vg B, were identified in serum from estrogen-treated barfin flounder (Verasper moseri). Structural changes of lipovitellins (Lvs) derived from the two Vgs were examined during vitellogenesis and oocyte maturation. Two Lvs, vLv A and vLv B, were identified electrophoretically and immunologically in postvitellogenic oocytes. Each appeared to be composed of distinct heavy chains (vLvH A, M(r) 107,000, and vLvH B, M(r) 94,000) and light chains (vLvL A, M(r) 30,000, and vLvL B, M(r) 28,000) when analyzed by SDS-PAGE. Results from N-terminal amino acid sequencing and Western blotting using antisera to vLvH A and vLvH B verified that there are two Vg polypeptides in serum from estrogen-treated fish, Vg A (M(r) 168,000) and Vg B (M(r) 175,000), which give rise to vLvH A-vLvL A and vLvH B-vLvL B, respectively. N-terminal sequencing revealed two sequences for both phosvitin and beta'-component, supporting the concept of duality for all three classes of Vg-derived yolk proteins. During oocyte maturation, native dimeric vLv B was dissociated into a native M(r) 170,000 monomer (oLv B). Meanwhile, vLv A was extensively cleaved including complete degradation of vLvH A into free amino acids. We propose that the quantitative ratio of vLv A to vLv B in postvitellogenic oocytes regulates the buoyancy of the spawned pelagic eggs by controlling availability of free amino acids which function as osmotic effectors during oocyte hydration. The vLv A/vLv B ratio likely also controls the proportional availability of different types of nutrients, free amino acids versus Lv, for use during embryonic development.

Mechanisms of lipid-body formation

Most organisms transport or store neutral lipids as lipid bodies - lipid droplets that usually are bounded by specific proteins and (phospho)lipid. Neutral-lipid bodies vary considerably in their morphology and are associated with an extremely diverse range of proteins. However, the mechanisms by which they are generated in plants, animals and microorganisms appear to share many common features: lipid bodies probably arise from microdomains of the endoplasmic reticulum (or the plasma membrane in prokaryotes) that contain lipid-biosynthesis enzymes, and their synthesis and size appear to be controlled by specific protein components.

Yolk formation and degradation during oocyte maturation in seabream Sparus aurata: involvement of two lysosomal proteinases

Oocyte growth within the follicle is preponderantly due to the accumulation of hepatically derived yolk protein (vitellogenin, VTG) by receptor-mediated endocytosis; once in the oocyte, VTG is partially processed and stored in yolk globules. In some pelagic egg-laying marine teleosts, additional cleavages of yolk proteins followed by a pronounced water uptake occur concomitantly with final oocyte maturation. The aim of this study was to establish the lysosomal enzymes involved in these two proteolytic processes that characterize oocyte maturation of seabream Sparus aurata. The enzymatic activities of several cathepsins were assessed in the various classes of oocytes. Changes in cathepsin B, D, and L activity were found depending on the oocyte maturation stage; cathepsin B and D were found to be at maximum level in early-vitellogenesis oocytes, and cathepsin L in mid-vitellogenesis ones. Cathepsin D and L were purified from seabream ovary, and their roles in VTG and lipovitellin (LV) proteolysis, respectively, were analyzed. Here we demonstrate directly that one of the catalysts for the intraoocytic processing of VTG in yolk proteins is cathepsin D; however, we cannot exclude also a role of cathepsin B in the same process. On the other hand, cathepsin L is responsible for the second proteolytic cleavage of the LV components. We postulate that the acquisition of buoyancy by eggs through the hydration process may be regulated by enzymatic activation at the appropriate time of oocyte maturation, this process probably being the key event in the reproduction of this marine pelagic egg spawner.

Purification, partial characterization and peptide sequences of vitellogenin from a reptile, the tuatara (Sphenodon punctatus)

Vitellogenin (Vg), a major precursor to egg yolk proteins, was purified from plasma of an estradiol-treated female tuatara (Sphenodon punctatus) by MgCl2-EDTA precipitation and DEAE-cellulose chromatography. The amino acid composition of tuatara Vg is similar to that of other vertebtate Vgs and contains a large proportion of serine (13.7 mol/100 mol of total amino acid). The amino acid sequences of the N-terminus of mature Vg (33 residues) and of several trypsin- and CNBr-generated peptides were determined. Six peptide sequences obtained from tuatara Vg could be aligned with Vg sequences from other vertebrates. Reduced and non-reduced forms of tuatara Vg have the same apparent molecular mass (approximately 218 kDa) when resolved by SDS-PAGE, indicating that inter-chain disulfide bonds are not a feature of the molecule in this species. Western blot analysis with anti-tuatara Vg antiserum indicated that at least some epitopes are shared among Vgs of turtle, alligator and tuatara.

A proteinase inhibitor from egg yolk of hen is an ovoinhibitor analog

A proteinase inhibitor, tentatively termed vitelloinhibitor, was purified from yolk of hen's ovarian follicles. It resembled egg-white ovoinhibitor not only in inhibitory spectrum (active for bovine trypsin and bovine chymotrypsin) but also in thermal stability, pH stability, antiserum reactivity and amino-acid composition. However, vitelloinhibitor had different molecular weight from that of ovoinhibitor. An alpha 2-proteinase inhibitor preparation, isolated from laying hen's serum in the present study, was found to exhibit two bands, and the larger one of the latter corresponded to vitelloinhibitor in molecular weight. The partial N-terminal amino-acid sequence of vitelloinhibitor was the same as those of the two components of serum inhibitor and all three agreed with that of ovoinhibitor. Vitelloinhibitor is likely to be an ovoinhibitor analog derived from a serum precursor, which might be the larger component of alpha 2-proteinase inhibitor.