Yolk Incorporation Research Articles

Possible regulation of the reproduction of the honey bee mite Varroa jacobsoni (Mesostigmata: Acari) by a host's hormone: Juvenile hormone III

With its first haemolymph meal from honey bee larvae the parasitic mite Varroa jacobsoni obtains different amounts of juvenile hormone III depending on the species and sex of the larva. Drone larvae of both Apis mellifera and A. cerana contain more than 5 ng/ml juvenile hormone in the haemolymph during the first 60 h after brood cell capping. Worker brood of A. mellifera contains 3–7 ng/ml whereas A. cerana does not reach 1 ng/ml during the first day after sealing. Juvenile hormone concentrations lower than 4 ng/ml seem to be one factor to prevent reproduction of the mites. Varroa, having parasitized on winter bees (low juvenile hormone titre) show 8% reproduction after beeing transfered to suitable brood cells. Mites from old summer bees (high juvenile hormone titre) show 76% reproduction. Varroa from winter bees transfered to larvae which were treated with juvenile hormone show 18%, and mites parasitizing winter bees sprayed with juvenile hormone showed 39% reproduction. Juvenile hormone effects could be demonstrated down to the cellular level in oögenesis. Our results suggest a model for a 2-fold influence of host juvenile hormone on Varroa: The first influence on the adult bee which might be necessary for the cell-entering behaviour and preparation of the ovary. The second one on the bee larva obviously triggers yolk incorporation into the eggs of the mite and induces oviposition.

Effect of carp gonadotropin (cGTH) and a fraction unabsorbed on concanavalin A-Sepharose obtained from cGTH on vitellogenesis in the hypophysectomized marine teleost Gobius niger

To investigate whether a differential potency on vitellogenesis exists between the carp gonadotropin (cGTH) and fraction I-cGTH (proteins from cGTH unbound on concanavalin A-Sepharose, which represent 5% of cGTH in weight), hypophysectomized Gobius niger were treated with the two hormonal preparations at the same level. Vitellogenesis was checked for synthesis of vitellogenin and yolk incorporation in the ovary by means of immunological studies and histological techniques (light and electron microscopy). In addition, increased synthesis of vitellogenin was induced by injection of estradiol 17β together with each gonadotropin to assess the action of the two hormonal preparations on vitellogenin incorporation. Oogenesis was enhanced by cGTH and fraction I-cGTH, and at the same dose levels both treatments produced a similar pattern of stimulation of vitellogenesis. Vitellogenin was found in all the blood samples of animals treated by the hormones (cGTH and fraction I-cGTH) alone. Vesicles of pinocytosis were detected by electron microscopy up to Stage IIIa of oogenesis. When a high synthesis of vitellogenin was induced by exogeneous estradiol 17β injections, the two gonadotropic preparations had similar effects in yolk incorporation. cGTH was not less potent than fraction I-cGTH in these processes even though the cGTH preparation contains only 5% of fraction I-cGTH. The contamination of cGTH by a small amount of material unbound on concanavalin cannot be solely responsible for the vitellogenic activity of cGTH which consists of 95% glycoproteins.

Effect of fat body excision on vitellogenic growth of oocytes inRana tigerina

In R. tigerina ovaries and fat bodies undergo annual cyclical changes. The fat bodies, well developed between September-March, begin to reduce in size from April onwards reaching a nadir in July-August. The decline in fat body size is correlated with the vitellogenic growth of oocytes and subsequent breeding. Bilateral fat body excision (fatectomy) in the first week of April retarded the vitellogenic growth of oocytes and therefore the mean size of the largest oocytes was significantly lower than in the sham operated controls (p<0.001) after 30 days as the incorporation of yolk was less. In the controls the vitellogenesis was complete. The gonadosomatic index and the mean weights of ovaries and oviducts did not change following fatectomy. These findings suggest that the fat bodies in the frog have a supporting role in the vitellogenic processes.

Development of physogastry in the queen of the fungus-growing termite Macrotermes michaelseni (Isoptera: Macrotermitinae)

Female reproductives of the fungus-growing termite Macrotermes michaelseni never showed signs of physogastry if they were kept in petri dishes to establish an incipient colony. During the 200 days of observation, their corpora allata volume, juvenile hormone titre and number of active ovarioles remained on a more or less constant level, and their gut was filled with soil. In contrast, these parameters are enhanced in partially and especially in fully physogastric queens, and these females had only a transparent liquid in the gut. Application of the juvenile hormone mimic ZR 515 to young females accelerated yolk incorporation, increased the number of active ovarioles and brought about the release of the soil from the gut. The same changes were induced by adding workers to increase the population of incipient colonies from about 45 to 400. This also resulted in an increase of the corpus allatum volume and of the juvenile hormone titre in young females. Their intestine was in this case filled with transparent liquid associated with the increased population of workers. It was, therefore, concluded that the development of physogastry depends on a positive feedback: the more workers are with the young female, the more nutrients are available and the more juvenile hormone the female produces, the more eggs are laid and the more workers can again develop to nurture the queen.

Antibody inhibition of vitellogenesis and oocyte maturation in salmon and flounder

Antisera to the two gonadotropic fractions from chum salmon pituitaries were injected into intact landlocked Atlantic salmon with yolky oocytes. Fish treated with antiserum to the maturational fraction had lower plasma levels of estradiol and vitellogenin than fish which received normal rabbit serum or an antiserum to the vitellogenic fraction. Fish injected with either antiserum showed lower incorporation of yolk into the ovary. Close to the spawning period antisera to the two gonadotropic fractions from chum salmon and winter flounder pituitaries were injected into intact landlocked salmon and winter flounder, respectively. Controls treated with normal rabbit serum, and fish injected with antisera to the vitellogenic fractions initiated germinal vesicle breakdown. Oocytes of fish treated with antisera to the maturational fractions did not begin the process of oocyte maturation. Incorporation of [ 3H]leucine and 33P into the water-insoluble yolk fraction of the oocytes was negligible in ovulated fish. The level of incorporation was lower in oocytes which had undergone germinal vesicle breakdown than in oocytes with germinal vesicles, although there were no changes detected in the plasma vitellogenin concentration.

Hormonal control of vitellogenesis in hypophysectomized winter flounder ( Pseudopleuronectes americanus Walbaum)

A surgical method of hypophysectomy employing a lateral approach to the brain is described; this technique results in total hypophysectomy and 90% survival. Hypophysectomy decreased the incorporation of 33PO 4 or [ 3H]leucine into yolk by the liver and abolished the accumulation of labeled yolk by the gonad. Estradiol treatment of hypophysectomized fish stimulates growth of the liver and hepatic synthesis of yolk proteins. No incorporation of yolk into the gonads was seen after estradiol treatment, and yolk protein accumulated in serum to higher levels than those seen in sham-operated fish. A glycoprotein preparation from teleost pituitaries, which should contain any classical gonadotropin, failed to stimulate gonadal incorporation of the yolk which accumulated in the serum. In contrast, the nonglycoprotein fraction of these pituitaries stimulated yolk incorporation into the ovary.

Haemolymph vitellogenin, juvenile hormone, and oöcyte growth in the adult cockroach Nauphoeta cinerea during first pre-oviposition period

In the cockroach Nauphoeta cinerea the incorporation of a protein of low solubility into the oöcytes begins at day 5 of its adult life. An immunologically identical protein appears in the haemolymph two days earlier. The concentration of this protein, i.e. ‘vitellogenin’ in the haemolymph increases up to the onset of yolk incorporation into the oöcytes. During ovarian development no correlation could be detected between vitellogenin titre and several other parameters (ovary dry weight, length of the basal oöcytes, haemolymph protein concentration, body weight and age when ovulation occurred). In young females vitellogenin titre depends on the age, i.e. the volume of the corpora allata and hence on the presence and the titre of JH. During the period of egg maturation the total haemolymph protein concentration generally tends to drop while materials not precipitable by trichloracetic acid circulate at higher concentration after ecdysis and before ovulation. Early decapitation prevents vitellogenin synthesis and oöcyte growth, but when JH is applied to decapitated females, the normal vitellogenin titre is re-established, ovarian development, however, cannot be fully resumed. A dose-response curve shows that serial application of the hormone is much more effective than single large doses. Farnesylmethylester, a JH mimic, is about a hundred times less active, but more persistent than JH. Copulation seems to enhance the synthesis and release of endogenous JH, while food and water uptake are necessary to guarantee and optimal ovarian development. JH and high vitellogenin titre never restore ovarian development in females deprived of food and/or water or in those decapitated shortly after ecdysis.

The influence of the endocrine system on reproductive behavior and development in grasshoppers

Whereas in the female of Gomphocerus rufus L. allatectomy and/or coagulation of the pars intercerebralis prevent sexual receptivity, sexual behavior in the male is unaffected by these operations. Removal of the corpora allata and coagulation of the pars intercerebralis at the same time, followed by reimplantation of corpora allata 6–12 days later, caused renewed incorporation of yolk in the terminal oocytes. It is suggested that the corpora allata act directly on the ovaries. The A′-cells of the ventral ganglionic chain in the female supply the flat neurohemal organs with neurosecretory material. Cauterization of the A′-cells results in a 50% decrease of egg production. Implantation of homogenates of flat neurohemal organs into pars-cauterized females can induce partial development of the terminal oocytes. It is suggested that the A′-cells produce part of the neurosecretory material necessary for egg development. Double operations in the male, in which the corpora allata were removed and the pars intercerebralis destroyed, followed by reimplantation of corpora allata 6–10 days later, reinitiated secretion in the hitherto inactivated accessory sex glands, and spermatophores were produced. It is suggested that the corpora allata affect the activity of the accessory sex glands in a direct way.

Oöcyte protection—A function of a corpus cardiacum hormone in the cockroach, Nauphoeta cinerea

In decapitated females of the cockroach Nauphoeta cinerea the oöcytes degenerate after 6 to 8 days. If corpora cardiaca are implanted into the body cavity, the oöcytes remain in good condition for at least 4 days longer, so that they can still react to implanted corpora allata with yolk incorporation. A hormone of the corpora cardiaca which may be stored neurosecretory material has a protective function for oöcytes. This resembles a protecting action of the corpora cardiaca on the prothoracic glands in the absence of corpora allata, which was demonstrated by Bodenstein.