The presence of a pregnenolone-binding factor in the copulatory organ of the migratory locust, Locusta migratoria migratorioides R. & F

The presence of estradiol-17beta and its specific binding sites in posterior silk gland of Bombyx mori

Although estradiol-17beta (E2) is known to be a vertebrate sex steroid, its presence in insects, particularly in Bombyx mori, has recently created considerable sensation regarding its significance in insect life. The specificity of estradiol action on the posterior silk gland (PSG) of B. mori has been previously assessed by the use of ICI-182780 as a specific receptor antagonist for estradiol. The present study provides evidence for systematic changes in the titer of estradiol-17beta in B. mori and its specific binding sites in the posterior silk gland according to the physiological age of fifth instar larvae. The changes in the estradiol level in the PSG after E2 treatment have also been determined to assess whether the administered estradiol has been taken up by the silk gland cells and whether the effect of exogenously administered E2 on the PSG is direct. The correlation in the profile of E2 binding sites with the endogenous estradiol level of PSG on different days of fifth instar larvae suggests that the level of binding sites in the PSG is regulated by the estradiol titer and that E2 may have some biological function in B. mori. Scatchard analysis of E2 binding sites in the PSG on 9th day of fifth instar larvae reveals that it consists of only one type of binding component. The dissociation constant (Kd) and maximum binding capacity (Bmax) of this putative E2 receptor have been found to be 8.98 +/- 0.744 nM and 55.8 +/- 5.53 fmol/mg cytosolic protein, respectively. The study thus indicates an involvement of the putative receptor in E2-mediated action on the silk gland of B. mori and paves a pathway for further evaluation of the physiological relevance of the presence of vertebrate steroids in insects.

Action of estradiol-17beta on the synthetic activity of the silk gland in Bombyx mori L

The effects of estradiol-17beta (E(2)) were studied on several metabolic parameters in the silk gland of Bombyx mori L. race Nistari. Topical application of different doses (0.05-4.0&mgr;g/g body weight) of E(2) on the first and second day of the fifth instar larvae showed a dose dependent effect when studied on the fifth day. A significant increase in silk gland weight and fibroin content was observed between the doses 0.05 and 0.1, and 0.1 and 1.0&mgr;g/g of E(2). A similar pattern of dose-dependent rise in DNA and RNA content of posterior silk gland (PSG) was observed with the doses of E(2) when the contents were expressed per pair of PSG. Higher doses of E(2) (2.0 or 4.0&mgr;g/g) demonstrated relatively less increase, unchanged level or a decrease in the above parameters in comparison to the control values. The glutamate-pyruvate transaminase of PSG showed a significant increase from 0.1 to 2.0&mgr;g/g of E(2) doses in comparison to the control value. Simultaneous injection of ICI-182780 (1.0&mgr;g/g), a very pure and specific antiestrogenic compound, with E(2) (1.0&mgr;g/g) caused a significant counteraction of E(2)-induced increase in silk gland activity, which was reflected in DNA and RNA content of PSG, wet weight and fibroin content of silk gland, and on glutamate-pyruvate transaminase activity. Cycloheximide (0.5&mgr;g/g), a protein synthesis blocker, caused a significant inhibition of the E(2) (1.0&mgr;g/g)-induced silk gland activity when treated along with estradiol. From this study it appears that estradiol has a specific effect on silk gland function and that it may act in a nuclear mediated way.

Comparative developmental physiology and molecular cytology of the polytrophic ovarian follicles of the blowfly Sarcophaga bullata and the fruitfly Drosophila melanogaster

1. The ovarian follicles of Sarcophaga and Drosophila consist of one oocyte and 15 nurse cells, the whole being surrounded by follicle cells. Although oocyte and nurse cells are genetically identical sibling cells, and although they are interconnected by cytoplasmic bridges, their physiology is very different. 2. The DNA content of the oocyte nucleus (germinal vesicle) never exceeds 4C, while values of polyploidisation up to 1024C have been measured in the nurse cells, this being dependent on their position within a follicle. 3. The nurse cell nuclei very actively synthesize RNA, while the germinal vesicle is almost completely inactive in this respect. 4. It has been possible to visualise the major cytoskeletal elements in the different ovarian cell types. Cellular markers of polarity and dorsoventral asymmetry have been described. 5. Electrophysiological measurements have been performed to find out whether or not the self-electrophoresis principle may be involved in polarised transport between nurse cells and oocyte. 6. Most of the vitellogenin is synthesized by the fat body but some follicle cells also synthesize small amounts. 7. The role of 20-OH ecdysone in the induction of vitellogenin synthesis in the fat body, as well as the presence of met-enkephalin like immunoreactivity in the gonads is well established in both species. Not so clear is the exact role of juvenile hormones and the nature of brain factors controlling ovarian development. 8. Drosophila has the advantage of its well documented genetics while the larger species Sarcophaga is preferable for the study of (electro-) physiological and cell biological mechanisms.

Pregnenolone, testosterone, and estradiol in the migratory locust Locusta migratoria; a gas chromatographical-mass spectrometrical study

Homogenates of ovaria as well as testes from the locust Locusta migratoria were analyzed for the presence of pregnenolone, testosterone, and estradiol by gas chromatography followed by mass spectrometry. Selected ion monitoring analyses revealed that the molecular ion and two characteristic fragment ions of pregnenolone, the molecular ion with its isotopes and two characteristic mass fragments of testosterone, and the molecular ion, its isotopes and four characteristic fragment ions of estradiol, were present at the proper retention times and with the correct abundance ratios.