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1.
The synthesis of vitellogenin (Vg) is induced by conspecific Vg (Vg1 and Vg2) and estradiol‐17β (E2) as demonstrated by the pattern of 3H‐serine incorporation in the liver and plasma proteins. The incorporation studies indicated that the label was first incorporated into the liver after which it appeared in the blood in both E2‐ and Vg‐treated male catfish. Since Vg was capable of inducing its own synthesis, experiments were conducted in females during preparatory–prespawning period (March–May) to make them gravid by implanting Vg pellets. Two implantations of 4 mg Vg1 pellets into female catfish with an interval of 15 days, followed by laboratory maintenance for 45 days of initial implantation showed a significant increment in ovarian weight with concomitant formation of yolky oocytes through synthesis and incorporation of Vg, whereas Vg2 implantation was not effective in this regard. Histological observation of yolky oocytes in Vg1‐treated group showed the peripheral migration of germinal vesicle (eccentric germinal vesicle), which indicates the onset of maturation. On 45th day, third implantation with 2 mg Vg pellets was performed and after 15 days, fish were hormonally induced with a single injection of hCG (2,000 IU/kg fish). Six groups were considered such as initial control, BSA‐implanted control, Vg1‐implanted, Vg2‐implanted, catfish collected from the field on the last day of the experiment and catfish collected during spawning period in this experiment with 3–7 fish in each group. Each of the experimental fish was sexually mature and the body weight was between 100 and 125 g. The percentage of ovulation and fertilization in the eggs of Vg1‐implanted group was 91% and 78%, respectively, which was almost similar to that of gravid female catfish collected during breeding period (July). The breeding performance in BSA‐ and Vg2‐treated females was very poor. The fertilized eggs were hatched in the laboratory conditions. Thus, in the female catfish, Vg1 not only induces vitellogenesis but also makes the oocytes viable for fertilization.  相似文献   

2.
Two forms of vitellogenin (Vg: Vg1 and Vg2) were purified from the plasma of estradiol-17β (E2)-treated Indian walking catfish, Clarias batrachus, by gel filtration and adsorption chromatography. Native Vg1 and Vg2 had apparent molecular masses of 375 and 450 kDa, respectively, and both Vgs resolved into two similar major bands (95 and 67 kDa) in SDS-PAGE under reducing condition. Polyclonal antisera raised against each form of Vg were absorbed with a combination of hypophysectomized male catfish serum proteins and alternate Vg to ensure specificity. Immunological analyses verified the presence of Vg1 and Vg2 in the plasma of female catfish. Homologous ELISAs were developed for Vg1 and Vg2 using their respective harvested antisera, which exhibited the detection limit of 100 ng ml?1 for Vg1 and 40 ng ml?1 for Vg2, and low level of cross-reactivity (not parallel to the standard) was found with alternate Vg in each assay. Treatment of male catfish with E2 induced both Vgs showing a proportionate ratio of Vg1 to Vg2 at 5.6:1. Plasma concentrations of both Vgs measured by ELISAs at different reproductive phases of field collected female catfish increased in accordance with the ovarian development, keeping the proportionate ratio of Vg1 to Vg2 at about 2:1 in fish undergoing vitellogenesis during prespawning period and 1:20 during spawning period, suggesting that Vg1 may be the major Vg to contribute in yolk formation, whereas Vg2, besides its role in yolk formation, may facilitate other physiological functions. The present study, thus, demonstrates the occurrence of two unequally synthesized Vgs in the catfish.  相似文献   

3.
Oocyte growth in most oviparous vertebrates including fish is due to the formation of yolk, and eggshell proteins (zona radiata proteins). Zonagenesis leads to the formation of zona radiata proteins in oocytes, which play an important role during oogenesis, whereas vitellogenesis leads to the formation of yolk in oocytes through a series of events during which the yolk precursor protein vitellogenin (Vg) is synthesized and secreted from liver into blood from where it is sequestered into the developing oocytes and thereafter proteolytically cleaved to form yolk proteins (YPs) and finally deposited in the ooplasm. Much research has been done in many fish species with respect to the number and nature of Vg and YPs and their probable functions during fish reproduction. Recent findings of multiplicity of Vg molecules in fishes reject the earlier view of a single-Vg model and have led scientists to explore the functions of individual Vg and their YP derivatives, lipovitellin, phosvitin, and β′-component. Two distinct types of Vg or Vg genes, containing or encoding the three YPs, have been detected in many teleosts. A third unusual, incomplete, phosvitin-poor Vg has been described recently in many fishes. In comparison to much of the information on vitellogenesis in many fishes very little is known for Indian fishes. In India research has been done in a few species such as the catfish, Heteropneustes fossilis and Clarias batrachus, the murrel, Channa punctatus and the Indian major carps, Labeo rohita and Cirrhinus mrigala. Immunological and biochemical analyses suggest the occurrence of multiple forms of Vg and their YP derivatives. The synthesis and incorporation of Vg are regulated by gonadotropin (GTH) and estradiol-17β (E2). A differential role between estrone (E1) and estriol (E3) has been demonstrated for Vg synthesis. Enzyme-linked immunosorbent assays (ELISAs) for Vg have been developed to measure plasma Vg. Finally the different roles of Vg1 (HAI) and Vg2 (HAII) on vitellogenesis have been demonstrated. However, more research remains to be carried out in other fish species with respect to the number and nature of Vg and YPs and their genes in order to describe their reproductive functions.  相似文献   

4.
We examined short-term changes in neuroendocrine function during the onset of vitellogenesis by introducing female mosquitofish into a warm environment. Activation of FSH cells occurred prior to vitellogenesis, which was characterized by the production of estradiol-17β (E2) by follicles and following vitellogenin (Vg) synthesis in hepatocytes. Incorporation of Vg into the oocytes was detected less than three days after fish were transferred into a warm aquarium.  相似文献   

5.
The egg yolk precursor, vitellogenin (VTG), was purified from blood plasma of striped bass by chromatography on hydroxylapatite or DEAE-agarose. The fish were first implanted with estradiol-17β (E2), which induced vitellogenesis. A rabbit antiserum (a-FSPP) raised against plasma from mature female striped bass, and then adsorbed with mature male plasma, was used to detect female-specific plasma protein (FSPP) in the chromatography fractions. Striped bass VTG (s-VTG) was collected from the peak fraction that was induced by E2, reacted with a-FSPP, and contained all detectable phosphoprotein. It appeared as a single band (Mr ≂ 170,000) in SDS-PAGE or Western blots using a-FSPP, and as a pair of closely-spaced phospholipoprotein bands in native gradient-PAGE, suggesting that there is more than one circulating form of s-VTG. The relationship of s-VTG to the yolk proteins was verified using a-FSPP. The antiserum reacted with the main peak from gel filtration of saline ovary extracts, and it specifically immunostained the two main bands in Western blots of the extracts and the yolk granules of mature oocytes. The amino acid composition of s-VTG was similar to that of VTG from other fish and Xenopus. A radial immunodiffusion assay for s-VTG was developed using a-FSPP and purified s-VTG as standard. The s-VTG was not detected in blood plasma of males, immature females, or regressed adult females, but plasma s-VTG levels were highly correlated with plasma E2 and testosterone levels, and oocyte growth, in maturing females. The results indicate that the maturational status of female striped bass can be identified by s-VTG immunoassay.  相似文献   

6.
The development of oocytes in association with changes in plasma concentrations of vitellogenin (Vtg), 17β-estradiol (E2) and testosterone (T) was investigated in maturing female greenback flounder Rhombosolea tapirina over the first part of a reproductive season. During vitellogenesis, increasing oocyte size was accompanied by the sustained elevation of plasma Vtg and E2. There was a marked increase in T towards the end of vitellogenesis.  相似文献   

7.
Immature eels positively responded to estradiol-17β (E2) injection in terms of vitellogenin (Vg) synthesis but not to growth hormone (GH) or 17α-methyltestosterone (MT) injection. However, injection of MT or GH combined with E2 strongly increased Vg synthesis. In in vitro experiments, eel hepatocytes treated with E2, GH, or MT alone did not produce detectable amount of Vg, whereas the combination of E2 with GH or MT, or both greatly increased Vg synthesis in the hepatocytes.  相似文献   

8.
Changes in the levels of plasma vitellogenin (Vg), estradiol (E2) and testosterone (T) were examined following gonadal development induced by carp gonadotropin treatment (cGTH) of freshwater female yellow and silver eels (Anguilla anguilla L.). The animals received injections of cGTH (250 μg kg−1 body weight) or saline vehicle three times a week, for 6 to 8 weeks. No effect of vehicle was observed. Steroidogenic activity of the ovary was stimulated by cGTH treatment as shown by the increase in circulating steroid levels in both stages. However, the responses of T, E2 and Vg differed according to the stage of development of eels. At the yellow stage, the initial steroid plasma levels were undetectable (< 0.01 ng ml−1) before treatment and ovarian steroidogenic activity was slightly stimulated following cGTH treatment; steroid levels reached their highest values after 3 weeks and 6 weeks of treatment for E2 (0.62 ± 0.13 ng ml−1 and T (0.33 ± 0.30 ng ml−1), respectively. The cGTH treatment slightly increased plasma Vg levels (0.2–0.7 μg ml−1 during the experiment compared with the initial values of the group. At the silver stage, the initial steroid levels were detectable (0.7 ng ml−1 for E2 and 0.1 ng ml−1 for T); cGTH treatment did not significantly increase plasma E2 level which remained at initial levels. Nevertheless, plasma T levels dramatically increased from 0.1 to 3 ng ml−1 and peaked after 1 or 2 weeks of cGTH treatment; a rapid increase in plasma Vg levels occurred, reaching its highest value at 5 mg ml−1 after 3 weeks of treatment. Thus, the steroid kinetic profiles in relation to the appearance of Vg in the plasma following cGTH treatment was closely related to androgen levels and there was a strong vitellogenic response induced by chronic cGTH treatment. In order to test if androgens could be implicated in the vitellogenic response, we evaluated the potencies of various androgens (testosterone and 5α-androstane-3β,17β-diol)in vivo andin vitro, associated with E2 to induce the production of Vg.In vitro experiments showed that Vg synthesis was induced by high doses (10−6 to 10−5 M) of androgen in the eel. Tamoxifen totally inhibited the action of androgens suggesting that androgens were acting through binding to the E2 receptor.In vivo, androgens given alone at 50 μg kg−1 3 times a week for 1 months had no significant effect on plasma Vg levels. In addition, E2-androgen cotreatment showed that the presence of androgen did not modify the vitellogenic response induced by E2.  相似文献   

9.
The relative efficacies of three natural estrogens viz., estrone (E1), estradiol-17β (E2) and estriol (E3) to induce synthesis of vitellogenin (Vg) and choriogenin (Chg) were assessed in primary hepatocyte cultures of the Indian freshwater spotted snakehead, Channa punctata. Hepatocytes were isolated from the spotted snakehead liver by a non-enzymatic protocol. Optimum culture conditions were standardized for ensuring their viability and functioning. Isolated hepatocytes were cultured for 48 h for monolayer formation and then exposed to various concentrations (0.001–10 μM) of the three estrogens. Competitive homologous ELISAs, developed and validated for spotted snakehead Vg and Chg were employed to determine the amounts of these two proteins secreted into the culture medium after 48 h of incubation. The results reveal that although all the three estrogens were effective in inducing the production of Vg and Chg in a dose-dependent manner, there were differences in their relative potencies. Of three estrogens, E1 was the least potent and could induce synthesis of Vg and Chg only at a minimum concentration of 0.5 μM; whereas significant levels of both the proteins were quantified in culture medium by exposing the hepatocytes to E2 or E3 even at a concentration of 0.001 μM. All three estrogens were effective in inducing synthesis of Vg and Chg in vivo also. These results suggest the possibility of employing the above in vitro experimental design to monitor the presence of estrogens/estrogen-like chemicals in natural waters, which could interfere with the estrogen receptor system of fish. This study further points to the possibility of using Chg, in addition to Vg, as a parameter for screening various chemicals for their estrogenic activity.  相似文献   

10.
The effect of methyl farnesoate (MF) administration on the vitellogenesis of the penaeoidean shrimp, Sicyonia ingentis, was studied. The short‐ and long‐term treatment effects as well as the effect of two MF injection regimens (0.1 and 1.0 μg MF/injection) were evaluated. The studies were also carried out to understand the pattern of vitellogenesis in eyestalk ablated adult and juvenile shrimps. A combination of endpoints, haemolymph vitellogenin (Vg) levels, gonadosomatic index (GSI) and histology, was used to study the effect of these treatments. The GSI increased in all the MF‐treated shrimp compared with the control shrimps. Although haemolymph Vg levels declined over the experimental period in all the treatments, the Vg levels decreased significantly only in the short‐term treatment with 1.0 μg MF. Similarly, haemolymph protein level also declined over the experimental period in all the treatment groups. However, except in the long‐term treatment with 0.1 μg MF, all treatments showed a significant decrease in haemolymph protein level. Conversely, in all eyestalk ablated adults and juveniles, haemolymph Vg, total protein and GSI increased over the experimental period, all of which were higher than the concurrent control. The discrepancy in the vitellogenic pattern between MF‐treated and eyestalk ablated shrimp was possibly due to the difference in the ovarian phase of the initial control. Although unilateral eyestalk ablation failed to induce vitellogenesis in juveniles, bilateral ablation induced vitellogenesis, which indicates that juveniles are competent to undergo vitellogenesis.  相似文献   

11.
We evaluated the annual process of oocyte and ovarian development of the planktivorous Amazonian catfish, the mapará (Hypophthalmus marginatus), aiming to support captive reproduction for domestication. A total of 149 females were captured from the Tocantins River at the Tucuruí Dam (3°49'55"S, 49°39'9"W) in 13 sampling events. For each individual, we evaluated ovary histology and plasma steroid concentrations. Two annual reproductive cycles, with similar characteristics, including a long period of rest, a short vitellogenic stage and a well‐defined spawning season from November to March, were described. A 17β‐estradiol (E2) rise and a 17α,20β‐dihydroxy‐4‐pregnen‐3‐one (DHP) peak were associated with vitellogenesis and spawning season, respectively, in the first cycle but not in the second reproductive cycle. In conclusion, the studied species presents a reproductive cycle similar to that of other migratory total spawners; however, unusually for this group of fish, there were three (but not two) batches of vitellogenic oocytes in “in maturation” and “mature” stage ovaries, pointing to the possibility of more than one spawn during the spawning season.  相似文献   

12.
ABSTRACT:   The annual reproductive cycle, including the first maturity of ovarian development and plasma levels of testosterone (T) and estradiol-17β (E2), was examined in female Japanese catfish Silurus asotus reared under natural conditions. In addition, the possible period that final oocyte maturation and ovulation can be induced by human chorionic gonadotropin (hCG) injection were investigated. Results showed that female Japanese catfish matured 1 year after hatching under reared conditions. The beginning of vitellogenesis was in March and ovarian development and plasma T and E2 levels peaked in June. Thereafter, the gonadosomatic index gradually decreased to October and regression of oocytes at the tertiary yolk globule stage was observed. Female Japanese catfish could be induced to final oocyte maturation and ovulation by hCG treatment during the period from June to September. In addition, the fertilization rates were relatively high and stable during this period. These results suggest that yearling female Japanese catfish can be used as brood stock for seed production. This is the first study to investigate the annual reproductive cycle in Japanese catfish. These data will provide useful information regarding brood stock management and seed production.  相似文献   

13.
Plasma estradiol-17 (E2), testosterone (T), 17,20-dihydroxy-4-pregnen-3-one (DHP) and 17,20,21-tri-hydroxy-4-pregnen-3-one (20-S) levels were measured by radioimmunoassay (RIA) in white perch (Morone americana) and white bass (M. chrysops) that were induced to undergo final oocyte maturation (FOM) with human chorionic gonadotropin (hCG). Plasma DHP levels increased in females of both species in association with oocyte germinal vesicle migration (GVM) and germinal vesicle breakdown (GVBD) and decreased thereafter. Plasma 20-S levels also increased with oocyte GVM in white bass, but were several-fold lower than DHP levels. Circulating E2 and T levels were greatest during GVM and GVBD in both species and decreased to low levels during oocyte hydration and ovulation. Follicles from white perch and white bass which received a priming injection of hCG in vivo, produced both DHP and 20-S in vitro after exposure to hCG and their oocytes underwent GVBD. Ovarian incubates from unprimed fish of either species produced only E2 and T and their oocytes did not complete GVBD. Oocytes from unprimed bass, but not perch, matured when follicles were exposed to hCG in vitro. Both trilostane and cycloheximide blocked in vitro production of DHP and 20-S and oocyte GVBD by white perch follices. DHP and 20-S were equipotent inducers of FOM in the GVBD bioassay. None of several other structurally-related steroids tested were effective within a physiological range of concentrations. These results indicate a role for DHP and 20-S in the control of FOM in white perch and white bass.  相似文献   

14.
In the present study, thiourea-induced thyroid hormone depletion and thyroxine (T4) ‘overdose’ were used as a strategy to understand the influence of thyroid hormones on ovarian recrudescence of juvenile (3-months-old), immature (8-months-old) and adult (1-year-old) air-breathing catfish, Clarias gariepinus. Thiourea-induced thyroid hormone depletion in juvenile catfish impaired ovarian development, but no significant effect was observed in immature catfish and during late stage of ovarian recrudescence of mature catfish. T4 treatment in females undergoing late stages of ovarian recrudescence induced rapid oocyte growth by promoting its early entry into maturational phase as evident from the presence of more number of vitellogenic and post-vitellogenic follicles, decrease in aromatse immunoreactivity and reduced estradiol–17β levels. Hence, thyroid hormones have an important role to play during early stages of ovarian development and vitellogenesis of catfish and also indicating that thyroid has a stage dependent effect on ovary.  相似文献   

15.
Adult female African catfish, Clarias gariepinus, were manipulated to enter the phase of ovarian recrudescence by induced ovulation and stripping. These females were exposed to various conspecific stimuli for 33 days. At the end of the experimental period, gonadosomatic indexes (GSIs) were higher in females which had received holding water from a mixed-sex population than in comparable controls. The effect was abolished when recipient females had been rendered anosmic, indicating the presence of chemical substances perceptible through olfaction. Fecundity estimates and histological analysis suggest that the increase in GSI due to pheromonal stimulation is caused by both an increased recruitment of oocytes into the stage of exogenous vitellogenesis and by an enhanced deposition of yolk material in the oocytes. It is concluded that male C. gariepinus release pheromones with a stimulatory effect on vitellogenesis. Neither anosmia itself nor metabolites in holding water affected ovarian recrudescence or body weight increase. The biological significance of such pheromones is discussed in the context of observations on reproduction of C. gariepinus made in the natural environment.  相似文献   

16.
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17.
In the Ivory Coast, grass carp (Ctenopharyngodon idella) have been integrated in the tilapia-based polyculture in order to increase pond productivity. In the tropical conditions prevailing there, female cycles seemed disrupted. We describe oogenesis in these conditions using histological observations, monitoring of individual cycles with intraovarian biopsies, endocrinal monitoring (development of a specific enzyme-linked immunosorbent assay (ELISA) for vitellogenin (Vg), measurement of plasma oestradiol-17β (E2) and testosterone (T)) and comparison with grass carp raised in Poland. We noted that oogenesis was blocked in all females at the migrating germinal vesicle stage, precluding ovulation or spawning without artificial induction. High rates of atypical post-vitellogenic oocytes (translucent, not filled with yolk granules) were observed in many females. Female individual cycles also displayed atypical features: cycles were sometimes (10% of females) blocked at the beginning of vitellogenesis (BV), for females displaying abnormally low E2 (0.5 ng/ml) and Vg (30 μg/ml) levels compared to “normal” females (1.4 ng/ml and 223 μg/ml, respectively). The duration of the cycles was highly variable among females (a few days to several weeks). Sexual cycles were unsynchronised (all the ovarian stages could be found for all seasons) and the number of females at the end of vitellogenesis (EV) was low (<40% most of the year). These characteristics raise problems for artificial induction of spawning in small-scale hatcheries: a large stock of broodfish is required as is regular checking of female broodstock with intraovarian biopsies to select responsive females.  相似文献   

18.
Ovarian developmental stages and serum steroid hormone levels were examined at six different times of day (0100, 0600, 1000, 1300, 1600, 2000 h) in a marine teleost, the Japanese whiting Sillago japonica, which has an asynchronous-type ovary containing oocytes at various stages of development and spawns every day during a period ranging up to three months. The largest oocytes in the ovaries at the active vitellogenic or post-vitellogenic stages were found between 0100 and 1300 h. Oocyte maturation indicated by germinal vesicle breakdown (GVBD) occurred at 1600 h, and ovulated oocytes were observed in the ovaries collected at 2000 h. These processes were accompanied by a significant daily change in serum steroid hormone levels. The serum level of estradiol-17β showed a peak in fish with mature oocytes sampled at 1600 h. In these fish, the second-largest oocytes in the ovaries were at the initial stage of vigorous vitellogenesis, the secondary yolk stage. Therefore the highest level of serum estradiol-17β was considered to be due to the second-largest oocytes. Testosterone levels remained low and constant throughout the experimental period. The serum levels of 17α,20β-dihydroxy-4-pregnen-3-one (17α,20β-diOHprog) peaked at 1600 h at which time all fish had mature oocytes. These results indicate that the Japanese whiting possesses a diurnal rhythm of oocyte development including vitellogenesis, oocyte maturation and ovulation, and further suggest that daily cycles in oocyte growth and maturation which simultaneously take place in an ovary are regulated by diurnal secretions of estradiol-17β and the maturation-inducing steroid, 17α,20β-diOHprog.  相似文献   

19.
In vivo induction of vitellogenin (VTG) in response to the administration of 17-estradiol (E2) was achieved and the protein was isolated by gel filtration column chromatography of plasma samples. Adult female trout were injected with the vitellogenic fraction every ten days from July to November and levels were measured by RIA from September to December. The results showed a significant decrease (p<0.01) in plasma E2 levels in injected females compared with the controls. In December, after finishing the treatment, the plasma E2 concentration increased, in injected females to reach a level similar to that of control females at vitellogenesis. The in vitro study showed that in early vitellogenic oocyte (from September) the presence of the vitellogenic fraction in the incubation medium causes a significant decrease (p<0.01) in the synthesis of E2 by the oocytes. These data suggest that the concentration of the VTG into the oocyte can alter VTG production by the liver, moderating the production of E2 by the ovary.  相似文献   

20.
A series of sixteen environmental experiments, conducted under controlled laboratory conditions during the refractory period in the reproductive cycle of the grey mullet, determined the effect of photoperiod and temperature on the vitellogenesis of intraovarian oocytes. Fish subjected to the natural light cycle and ambient water temperatures (24–26°C) served as controls. A classification of stages of vitellogenesis (I–V) is used to determine the percentage composition of oocytes for each fish at intervals throughout the experiment following sampling in vivo.Onset of vitellogenesis is timed by the environmental conditions. A retarded photoperiod, irrespective of preconditioning photoperiod, plays a dominant role in stimulating oocyte growth. Temperature regulates vitellogenesis towards functional maturity. The combination of retarded photoperiod (6L/18D) and constant temperature of 21°C is the most effective for the completion of vitellogenesis of oocytes to functional maturity.Regular injections of pregnant mare's serum gonadotropin (PMSG) at 1 IU/g body weight are effective in initiating vitellogenesis.  相似文献   

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