Isolation of H-SF substances, the high-molecular-weight precursors of egg envelope proteins, from the ascites accumulated in the oestrogen-treated fish, Oryzias latipes

Medaka, Oryzias latipes, egg envelopes are created by ovarian-expressed ZP proteins and liver-expressed choriogenins

The medaka (Oryzias latipes) egg envelope (chorion) is composed of three major glycoproteins, Zona Interna (ZI)-1, -2, and -3, that originate in the spawning female liver as the precursor proteins Choriogenin (Chg.)H, Chg.Hm, and Chg.L, respectively. These ZI and Chg. proteins contain a structural ZP protein domain that is conserved among the egg envelope proteins of all animals. While ovarian expression of ZP proteins (e.g., ZPCs and ZPB) has been reported in medakas, the functions of these proteins remain unknown. Thus, the present study aimed to determine whether the ovary-expressed medaka ZP protein, mZPC5, is involved in forming the chorion matrix.The mZPC5 gene (mzpc5) was expressed in the ovaries but not the livers of mature female medakas, as shown by reverse transcription-polymerase chain reaction assays with mzpc5-specific primers. In situ hybridization analysis revealed that ovarian mzpc5 expression was restricted to the ooplasm of early (stage I-III) previtellogenic oocytes, and its expression signal weakened with oocyte growth. Following sodium-dodecyl-sulfate polyacrylamide gel electrophoresis (SDS-PAGE) and Western blotting analysis with anti-mZPC5 antibodies, two immunoreactive proteins were detected in the ovary and chorion extracts. These proteins were approximately 50 and 74 kDa in size, like ZI-3 and ZI-2, respectively.Immunohistochemical assays using anti-mZPC5 and anti-Chg.H antibodies localized the mZPC5 protein in the ooplasm of early previtellogenic oocytes. With oocyte growth, mZPC5 tended to accumulate in the chorion, co-localizing with Chg.H.We previously showed that ovary-expressed ZP proteins could not compensate for Chg.L function loss in gene knock-out (chg.l -/-) medakas. As in our previous study, the chg.l-/- females produced oocytes with thin chorions, resulting in infertile soft eggs. However, in the present study, mZPC5 and Chg.H were co-localized in the chg.l-/- chorions. These results suggested that in the medaka previtellogenic oocyte, 1) mZPC5 is secreted from the ooplasm and deposited on the outer surface of its plasma membrane, creating the thin chorion layer; and 2) following the accumulation of liver-derived Chgs., the 3D structure of the chorion matrix is formed cooperatively with mZPC5 and Chgs. during oogenesis. More research is needed to confirm the functions of mZPC5 in chorion structure and physiology.

Targeted deletion of liver-expressed Choriogenin L results in the production of soft eggs and infertility in medaka, Oryzias latipes

Egg envelopes (chorions) in medaka, Oryzias latipes, are composed of three major glycoproteins: ZI-1, - 2, and - 3. These gene-encoded chorion glycoproteins are expressed in the liver and/or ovarian oocytes of sexually mature female fish. In medaka, the glycoproteins produced in the female liver are induced by estrogen as Choriogenin (Chg.) H and Chg. H minor (m), which correspond to the zona pellucida (ZP) B (ZPB) protein in mammals, and Chg. L, which corresponds to ZPC in mammals. Chg. H, Chg. Hm, and Chg. L, are then converted to ZI-1, - 2, and - 3, respectively, during oogenesis in medaka ovaries.In the present study, we established a medaka line in which the chg.l gene was inactivated using the transcription activator-like effector nuclease (TALEN) technique. Neither intact chg.l transcripts nor Chg. L proteins were detected in livers of sexually mature female homozygotes for the mutation (homozygous chg.l knockout: chg.l-/-). The chg.l-/- females spawned string-like materials containing "smashed eggs." Closer examination revealed the oocytes in the ovaries of chg.l-/- females had thin chorions, particularly at the inner layer, despite a normal growth rate. In comparing chorions from normal (chg.l+/+) and chg.l-/- oocytes, the latter exhibited abnormal architecture in the chorion pore canals through which the oocyte microvilli pass. These microvilli mediate the nutritional exchange between the oocyte and surrounding spaces and promote sperm-egg interactions during fertilization. Thus, following in vitro fertilization, no embryos developed in the artificially inseminated oocytes isolated from chg.l-/- ovaries. These results demonstrated that medaka ZI-3 (Chg.L) is the major component of the inner layer of the chorion, as it supports and maintains the oocyte's structural shape, enabling it to withstand the pressures exerted against the chorion during spawning, and is essential for successful fertilization. Therefore, gene products of oocyte-specific ZP genes that may be expressed in medaka oocytes cannot compensate for the loss Chg. L function to produce offspring for this species.

Establishment of proprotein convertase, furinA knocked-out lines in medaka, Oryzias latipes, and unique form of medaka furin-like prorprotein convertase (mflPC)

Furin is a member of the subtilisin-like proprotein convertase family. Medaka furin-like proprotein convertase (mflPC), a unique form of medaka FurinA (mFurinA) (GenBank accession no. AB092685.1) was cloned from the ovary cDNA library. Compared to human furin (GenBank accession no. NM_002569.3) and mFurinA in the structural motif of mflPC, only the catalytic domain and the N-terminal region of the P domain are highly conserved, but more C-terminal domains are truncated. Based on our research, there three forms of furin, mFurinA, mflPC and mFurinB that exist in medaka. These three genes are expressed in the developing embryos and ubiquitously in adult tissues. To investigate the function of mFurinA and mflPC, as a first step, mFurinA KO lines were established. The mFurinA KO larvae with abnormal phenotypes exhibit edema, abnormal body fluid accumulation in the pericardial and yolk sacs, enlarged hearts, clogged blood vessels, structurally weak eyes, and a very short life. The data suggests that abnormal processing of TGF-β may be one of the causes of these disorders. FurinA KO medaka is a good model for the study of human diseases such as Fraser Syndrome and Marfan syndrome. The creation of human genomic disorder models using recently advanced genome editing procedures informs us of the function of key molecules and their role in causing equivalent human disorders and will be useful as a tool to identify the mechanisms involved.

Choriogenin and vitellogenin in red lip mullet (Chelon haematocheilus): purification, characterization, and evaluation as potential biomarkers for detecting estrogenic activity

Two vitelline envelope precursors (choriogenin H: Chg H; choriogenin L: Chg L) and an egg yolk precursor (vitellogenin B: VgB) were purified from red lip mullet. The mass of intact Chg H and Chg L were estimated to be approximately 215 kDa and approximately 69 kDa, respectively. In SDS-PAGE, Chg H and Chg L separated to positions corresponding to approximately 51 kDa and approximately 44 kDa, respectively. The mass of intact VgB was approximately 530 kDa and resolved into a polypeptide of approximately 185 kDa in SDS-PAGE. Specific antisera were raised against each purified protein and specific immunoassays were developed. When Chg H, Chg L and VgB were induced in the serum of immature mullet by injection with various doses of estradiol-17beta (E(2)), VgB exhibited the most sensitive response exhibiting high variation in its induced levels. The variation in induced levels of Chg H and L was relatively minimal although induction required higher doses of E(2) than with VgB. Serum samples obtained from immature mullet populations collected from their natural habitat exhibited similar profiles in the levels of these proteins. The present study suggests that the utilization of multiple biomarkers holds great importance for the reliable and accurate evaluation of estrogenic activity in aquatic environments.

Inoculation of female American black bears (Ursus americanus) with partially purified porcine zona pellucidae limits cub production

The present 2-year study investigated the feasibility of using porcine zona pellucidae (pZP) as antigen for immunocontraception in American black bears. Sows, 3–6 years of age, were administered either two doses of 250 µg pZP with Freund’s adjuvant (n = 10) or adjuvant alone (n = 5), one in April and one in May, and were kept away from the boars until June. Serum samples were collected before injections and before denning (November). The presence of sows with cubs at side was observed during premature emergence from denning. First-year results indicated that anti-pZP antibody titres in vaccinated sows were 2.5–9.0-fold (range) higher compared with non-vaccinated sows and that the vaccinated sows were threefold less likely to become pregnant (P = 0.167). Control and vaccinated bears produced 1.6 and 0.2 cubs per sow, respectively (P = 0.06). The second-year study investigated the feasibility of using pZP sequestered in a controlled-release pellet and a water-soluble adjuvant (QS-21) to avoid regulatory problems associated with Freund’s adjuvant. Sows in the treatment group (n = 22) were administered a single dose of an emulsion of 250 µg pZP and 150 μg QS-21 plus a pellet containing 70–90 µg pZP for delayed release as booster dose. Control sows (n = 5) received the QS-21 adjuvant in pellet alone. Serum samples were collected before inoculations (April) and before denning (November). Seven cubs were born to the five control sows, but none was born to the 22 vaccinated sows (P < 0.001). Anti-pZP antibody mean absorbance ratios in control sows remained at background levels, whereas vaccinated sows had ratios fourfold higher than controls. Two-dimensional polyacrylamide gel electrophoresis and immunohistochemical localisation confirmed immunoreactivity of sera from inoculated bears. We conclude that cub production in the American black bear can be effectively limited with either two injections of 250 μg pZP or a single inoculation of partially purified pZP sequestered in controlled-release pellets.

Induction of hepatic choriogenin mRNA expression in male marine medaka: a highly sensitive biomarker for environmental estrogens

Teleost choriogenins, precursors of the inner layer subunits of egg envelope, have been recently introduced as sensitive biomarkers for exposure to estrogenic compounds. In this study, two full-length cDNAs-ojChgH and ojChgL which encode the choriogenin H and L forms, respectively, were cloned from the marine medaka, Oryzias javanicus. The deduced protein sequences of ojChgH and ojChgL are highly similar to the corresponding homologues in the freshwater medaka (O. latipes) with identities of 77.2 and 87.6%, respectively. Phylogenetic analysis indicated that ojChgH and ojChgL are members of two different classes of liver-specific ZP-domain containing proteins (ZPB and ZPC, respectively). Computer analysis of ca. 2 kb of the 5'-flanking sequences of ojChgH and ojChgL revealed that both genes contain a number of putative estrogen response elements (EREs) and/or half-site EREs. In vivo mRNA expression patterns of the genes were examined by quantitative real-time RT-PCR. ojChgH is expressed exclusively in the liver while ojChgL is co-expressed in the liver (major) and ovary (minor). Exposure of fish to waterborne 17beta-estradiol (E2) at environmentally relevant concentrations (1, 5, 10 and 100 ng/L) resulted in dose-dependent induction of both genes in the liver, with higher sensitivity and magnitude of induction in males than in females. In the male liver, induction of ojChgH is more sensitive to E2 than that of ojChgL and two other estrogen-responsive genes, estrogen receptor alpha (ojERalpha) and vitellogenin (ojVTG). The lowest-observed-effect concentration (LOEC) of E2 on induction of hepatic ojChgH mRNA is 1 ng/L. In the ovary, expression of ojChgL is non-responsive to E2 treatment. In conclusion, the present study suggested that induction of hepatic ojChgH mRNA in male fish may be a highly sensitive biomarker for exposure to environmental estrogens.

Effect of porcine zonae pellucidae immunisation on ovarian follicular development and endocrine function in domestic ewes (Ovis aries)

Domestic ewes (Ovis aries) were immunised with porcine zonae pellucidae (pZP) or pZP conjugated to keyhole limpet haemocyanin (KLH) in adjuvant(s) to examine the feasibility of the species to serve as a model for further development of pZP-based vaccines in ungulates. Two immunisation groups were employed, with a third group receiving only adjuvant (n = 5 per group). Early in the study, oestrous activity was monitored by the use of a vasectomised ram fitted with a marking harness. Eventually, ewes were exposed to an intact ram for breeding. In addition, weekly serum and every-other-day faecal samples were collected to measure pZP antibodies and progesterone metabolite concentrations respectively. At the conclusion of the study, fecundity was established, and ovarian tissue was examined. Ewes immunised against pZP : KLH with adjuvant produced minimal antibody absorbance levels, displayed normal oestrous cycles, became pregnant upon introduction of the intact ram and exhibited normal ovarian histopathology. Ewes immunised against pZP with adjuvant produced high antibody absorbance levels, were acyclic following primary immunisation and were infertile. Examination of the ovarian tissue revealed atrophic changes that included: (1) the absence of growing follicles; (2) significant reduction in the number of primordial follicles; and (3) the presence of abnormal granulosa cell clusters lacking oocytes. Antisera displayed immunoreactivity to the major components of pZP, and immunohistochemical labelling of ovarian tissue showed specificity to the ZP. These data are the first generated in an ungulate species showing deleterious effects of pZP immunisation on folliculogenesis and oestrous cyclicity.

Annual changes in serum levels of two choriogenins and vitellogenin in masu salmon, Oncorhynchus masou

Annual changes in serum levels of two chorion precursors, choriogenin H (Chg H) and choriogenin L (Chg L), vitellogenin (Vg) and estradiol-17beta (E2) were quantified in masu salmon, Oncorhynchus masou, using specific immunoassays. Serum Chg levels were higher than Vg during the previtellogenic growth phase when circulating E2 levels were low ( approximately 0.1 ng/mL), suggesting higher sensitivity of Chg to E2. When oocyte growth shifted to the vitellogenic phase, Vg levels increased and became the most abundant in serum coincident with elevations of E2 and GSI. Chg H, Chg L and Vg peaked 1 month prior to ovulation at 0.61+/-0.08, 0.98+/-0.18 and 10.93+/-3.24 mg/mL, respectively. These results suggest that chorion formation by Chgs occurs prior to vitellogenesis and that the sensitivity of Chgs to low circulating E2 is closely related to the sequential events of oocyte growth.

Persistence of anti-zonae pellucidae antibodies following a single inoculation of porcine zonae pellucidae in the domestic equine

In this study of equids, we investigated the antibody response and the effect on the estrous cycle following a single inoculation of porcine zonae pellucidae (pZP) employing controlled-release methodology. We also investigated the use of two different water-soluble adjuvants as an alternative to oil-based adjuvants. Twenty-seven domestic mares were inoculated with various formulations of pZP and adjuvant. We showed that the anti-pZP antibodies generated as a result of the inoculations persisted for at least 43 weeks (length of the study). Of the various formulations used in the study, pZP and QS-21 water-soluble adjuvant, administered in combination with an emulsified preparation of pZP and Freund’s Complete Adjuvant generated a significantly (P < 0.05) higher titer of anti-pZP antibodies when compared with other formulations employing the water-soluble adjuvant, Carbopol. Hormone analyses for cyclicity indicated a high incidence and extended duration of persistent corpora lutea among the treated mares. The positive control group of mares receiving two standard inoculations of pZP and Freund’s Complete and Incomplete Adjuvants, as well as the placebo group of mares injected with QS-21 only, also exhibited high incidences of persistent corpora lutea. However, all mares eventually returned to normal cyclicity. The basis for the high incidence and extended duration of persistent corpora lutea was unexplained. The results demonstrate for the first time the persistent generation of anti-pZP antibodies following a single inoculation of pZP incorporated into a controlled-released preparation in the horse. This study further suggests that a single inoculation of pZP sequestered in a controlled-release lactide-glycolide polymer may serve as an alternative to traditional two-inoculation protocols for contraception investigations in the equine.

Identification of the herbicide Surflan and its active ingredient oryzalin, a dinitrosulfonamide, as xenoestrogens

Numerous environmental contaminants have been identified as endocrine disruptors (EDs)--substances that alter endocrine homeostasis by interfering with the biological action, production, or pharmacokinetics of endogenous hormones. Xenoestrogens are those EDs whose biological activity is similar to endogenous estrogen. This report presents data that identified Surflan, a proprietary herbicide emulsion, and its active ingredient oryzalin as xenoestrogens. In vitro, Surflan and oryzalin activated an estrogen-inducible reporter gene, and oryzalin competitively displaced 17beta-estradiol from the estrogen receptor. In vivo, Surflan and oryzalin induced expression of estrogen-regulated high-molecular-weight choriogenin genes in medaka (Oryzias latipes). These results are consistent with the characteristics of previously identified xenoestrogens and indicate that Surflan and oryzalin have the potential to adversely affect numerous estrogen-regulated biological processes.

Identification of choriogenin cis-regulatory elements and production of estrogen-inducible, liver-specific transgenic Medaka

Choriogenins (chg-H, chg-L) are precursor proteins of egg envelope of medaka and synthesized in the spawning female liver in response to estrogen. We linked a gene construct chg-L1.5 kb/GFP (a 1.5 kb 5'-upstream region of the chg-L gene fused with a green fluorescence protein (GFP) gene) to another construct emgb/RFP (a cis-regulatory region of embryonic globin gene fused with an RFP gene), injected the double fusion gene construct into 1- or 2-cell-stage embryos, and selected embryos expressing the RFP in erythroid cells. From the embryos, we established two lines of chg-L1.5 kb/GFP-emgb/RFP-transgenic medaka. The 3-month-old spawning females and estradiol-17beta (E2)-exposed males displayed the liver-specific GFP expression. The E2-dependent GFP expression was detected in the differentiating liver of the stage 37-38 embryos. In addition, RT-PCR and whole-mount in situ hybridization showed that the E2-dependent chg expression was found in the liver of the stage 34 embryos of wild medaka, suggesting that such E2-dependency is achieved shortly after differentiation of the liver. Analysis using serial deletion mutants fused with GFP showed that the region -426 to -284 of the chg-L gene or the region -364 to -265 of the chg-H gene had the ability to promote the E2-dependent liver-specific GFP expression of its downstream gene. Further analyses suggested that an estrogen response element (ERE) at -309, an ERE half-site at -330 and a binding site for C/EBP at -363 of the chg-L gene played important roles in its downstream chg-L gene expression. In addition, this transgenic medaka may be useful as one of the test animals for detecting environmental estrogenic steroids.

Choriogenin mRNA induction in male medaka, Oryzias latipes as a biomarker of endocrine disruption

The fish egg envelope has been known to consist of two distinct layers. The outer layer is thin and is formed around the oocytes during the later stage of previtellogenic development. The inner layer, called zona radiata, is thicker than outer layer and occupies most of the egg envelope. Zona radiata proteins of medaka (Oryzias latipes) consist of two major subunit groups, ZI-1,2 and ZI-3. The precursors of ZI-1,2 and ZI-3 have been named choriogenin H and choriogenin L, respectively. They are synthesized in the liver in response to estrogen, and then released into the blood stream and incorporated into the zona radiata in sexually matured female medaka. However, choriogenin is also induced in male medaka when the fish are exposed to estrogenic chemicals. Choriogenin can be suggested as a possible biomarker of endocrine disruption in fish, however, relatively little has been known about chorogenin gene expression by estrogenic chemicals. In this study, full sequence of choriogenin L DNA was identified, and measurement of choriogenin mRNA induction was established in medaka by use of RT-PCR technique. Also estrogenic effects of industrial chemicals were evaluated by this tool. When mature male medaka was treated with bisphenol A, nonylphenol, and 17alpha-ethinylestradiol for 6 days, respectively, the expression levels of choriogenin L and H mRNA were elevated in treated groups. The induction of choriogenin subunits expression by these chemicals showed a dose-dependent pattern and choriogenin L was found to be more sensitive than choriogenin H.

Purification of serum precursor proteins to vitelline envelope (choriogenins) in masu salmon, Oncorhynchus masou

Three vitelline envelope-related proteins (VERPs), very-high-molecular-weight VERP (vhVERP), high-molecular-weight VERP (hVERP) and low-molecular-weight VERP (lVERP) were purified from female masu salmon serum. The apparent molecular weights of vhVERP, hVERP and lVERP, in their native state, were 520, 88 and 54 kDa, respectively, by gel-filtration chromatography. Very-high-molecular-weight VERP comprises two subunits, corresponding to 175 and 126 kDa. On SDS-PAGE, hVERP and lVERP migrate at 53 and 47 kDa, respectively. Amino acid analysis of vhVERP and hVERP showed that they share a high content of glutamic acid and proline. By contrast, lVERP is rich in glutamic acid and asparatic acid. These features are in good agreement with the amino acid composition of the vitelline envelope. Immuno-biochemical analysis suggested that vhVERP is derived from hVERP by polymerization and/or aggregation. Antibodies against hVERP and lVERP specifically immunostained the vitelline envelope and liver of female masu salmon. In addition, both hVERP and lVERP were induced in the serum of estrogen-treated male fish. Taken together, it is suggested that hVERP and lVERP are homologous molecules with choriogenin H and choriogenin L in medaka, respectively. These results indicate that hVERP and lVERP are precursor proteins to the vitelline envelope (choriogenins) in masu salmon.

The third egg envelope subunit in fish: cDNA cloning and analysis, and gene expression

The inner layer of the egg envelope of a teleost fish, the medaka, Oryzias latipes, consists of two major subunit groups, ZI-1,2 and ZI-3. On SDS-PAGE, the ZI-1,2 group presents three glycoprotein bands that were considered to be composed of a common polypeptide moiety derived from their precursor, choriogenin H (Chg H). ZI-3 is a single glycoprotein derived from the precursor, choriogenin L (Chg L). In the present study, a fraction of a novel subunit protein was found in the V8 protease digest of ZI-1.2 that was partially purified from oocyte envelopes. This protein fraction was not present in the purified precursor, Chg H. By RT-PCR employing the primers based on the amino acid sequence of this fraction, a cDNA for the novel subunit was amplified, and a full-length clone of the cDNA was obtained by screening a cDNA library constructed from the spawning female liver. The clone consisted of 2025 b.p. and contained an open reading frame encoding the novel protein of 634 amino acids. This protein included Pro-X-Y repeat sequences in two-fifths of the whole length from its N-terminus. Northern blot analysis revealed that the gene expression for this protein occurred in the liver but not in the ovary of spawning female fish. This protein is considered as the third major subunit of the inner layer of the egg envelope of medaka.

Cloning of cDNA and estrogen-induced hepatic gene expression for choriogenin H, a precursor protein of the fish egg envelope (chorion)

A cDNA for choriogenin H (Chg H; formerly high-molecular weight spawning female-specific substances, or H-SF), a precursor protein of the inner layer subunits of egg envelope (chorion) of the teleost fish, Oryzias latipes, was cloned and analyzed. The clone consisted of 1913 bp and contained an open reading frame encoding a signal peptide of 22 aa and Chg H protein of 569 aa. The Chg protein possessed three potential N-glycosylation sites and Pro-X-Y repeat sequences in the first two-fifths of the N terminus. There were amino acid sequence similarities between Chg H and a gene product expressed in the liver of female winter flounder during vitellogenesis. Moreover, the amino acid sequence of Chg H is similar to that of ZP2 rather than ZP3 of zona pellucida of some mammals. Northern blot analysis indicated that gene expression for Chg H occurred only in the livers of spawning female fish and 17beta-estradiol-treated male fish, but not in the ovary of the spawning female fish. Gene expression for Chg H and Chg L (formerly low-molecular weight spawning female-specific substance, or L-SF) was induced and increased in parallel in the male fish liver after 17beta-estradiol treatment.

Studies on the hatching enzyme (choriolysin) and its substrate, egg envelope, constructed of the precursors (choriogenins) in Oryzias latipes: a sequel to the information in 1991/1992

Enzymatic hatching of fish embryos is caused by a sequential occurrence of many elementary processes from the commitment of the hatching gland cells to the emergence of the embryos. Molecular biological approaches to the formation, properties and function of the hatching enzyme should be required for elucidation of the enzymatic hatching, since this enzyme is a key molecule to analyze these processes. Besides them, there are some other processes indirectly related to hatching, e.g., formation and hardening of the egg envelope. The present article describes the results of our studies on some of the above-mentioned problems in the fish, Oryzias latipes, which have been obtained mostly in the early 1990s.

Evaluation of solubilizing methods of the egg envelope of the fish, Oryzias latipes, and partial determination of amino acid sequence of its subunit protein, ZI-3

The inner layer of most teleostean egg envelopes, especially those after hardening, is almost insoluble in ordinary solvent, and therefore the inner layer of only the unhardened egg envelope has been subjected to solubilization with some potent solvents. We comparatively evaluated the methods of solubilization of the inner layer of egg envelope of medaka, Oryzias latipes, with SDS, urea and guanidium chloride (GuHCI). Analysis of the solubilized samples by SDS-polyacrylamide gel electrophoresis, comparison of their amino acid compositions or peptide maps using high-performance liquid chromatography and partial determination of their amino acid sequences showed that SDS and GuHCI were appropriate for solubilization and characterization of the envelope. Urea solubilization resulted in some artificial modifications of lysine and/or cysteine residues of envelope proteins. Partial determination of amino acid sequence of a subunit, ZI-3, isolated from the SDS-or GuHCI-solubilized envelope strongly suggested the identity of the envelope subunit, ZI-3, and its precursor, L-SF.