Francine Goltzene

Ecdysone titre and metabolism in relation to cuticulogenesis in embryos of Locusta migratoria

Abstract Eggs of Locusta migratoria contain remarkably high concentrations of ecdysone and several other ecdysteroids. During the time-span of embryonic development (11 days) 4 distinct peaks of ecdysone concentration (up to 8 μM) are observed in the egg, demonstrating the ecdysiosynthetic capacity of the embryo. Only during postblastokinetic development, is ecdysone efficiently hydroxylated to 20-hydroxyachieved through conjugation. On the basis of optical and electron microscopic observations, we have been able to correlate precisely each of the four peaks of ecdysone concentration in the egg with the time of deposition of a cuticle by the embryonic tissues (peak 1: serosal cuticle; peak 2: first embryonic cuticle; peak 3: second embryonic cuticle; peak 4: third embryonic cuticle).

Involvement of ecdysone in the control of meiotic reinitiation in oocytes of Locusta migratoria (Insecta, orthoptera)

Abstract Following their biosynthesis in the follicle cells of vitellogenic ovaries, large amounts of ecdysteroids pass into the oocytes where they accumulate and persist during ovulation and egg-laying. The present paper shows that free ecdysone is unevenly distributed in the oocytes exhibiting the highest concentrations in the region of the posterior pole where the final sequences of nuclear maturation, including germinal vesicle breakdown (GVBD), occur. A correlative study indicates that the concentrations of free ecdysone in this region are particularly high (10 to 20 μ M ) during two periods of meiotic reinitiation observed in the oocytes: reinitiation I, leading from prophase I to metaphase I with GVBD; and reinitiation II, from metaphase I to the end of meiosis. In vitro incubations of oocytes in meiotic arrest (prophase I) in the presence of exogenous ecdysone demonstrate that complete reinitiation (including GVBD) can be triggered in a dose-dependent manner by this hormone.

Experimental evidence for a neuroendocrine control of ecdysone biosynthesis in adult females of Locusta migratoria

Abstract The considerable increase in ecdysteroid concentration which occurs in normal Locusta ovaries at the end of each cycle of oocyte maturation is prevented if the median neurosecretory cells of the pars intercerebralis are cauterized, or if the corpora cardiaca are excised 24 hr before the onset of ecdysone synthesis in normal females. Implantation of additional brain-corpora cardiaca complexes into young vitellogenic females advances the time of ecdysone synthesis by some 12 hr. Oocyte growth itself is not affected in these different types of experiments. It is inferred from the data of the present study that ecdysone synthesis in the follicle cell epithelium of maturing Locusta ovaries is stimulated by a neurohormone produced in the median neurosecretory cells of the pars intercerebralis and secreted into the blood via the corpora cardiaca.

Role of the follicle cells and the oocytes in ecdysone biosynthesis and esterification in vitellogenic females of Locusta migratoria

Summary Follicle cells have been dissected from vitellogenic ovaries and isolated by collagenase treatment and centrifugation. The cell pellets were incubated with high specific activity tritiated 2-deoxyecdysone and 2,22,25-trideoxyecdysone. Both molecules were readily converted to ecdysone. A privileged sequence of hydroxylations was evidenced for the trideoxyecdysteroid: C-25; C-22; C-2. A significant amount of 2-deoxyecdysone and ecdysone was esterified to Helix hydrolysable conjugates both by the isolated follicle cells and by ooplasm preparations. In the ooplasm, the C-2 hydroxylase, but not the C-22 and C-25 hydroxylation systems, was found to be active. A relatively low level of C-20 hydroxylation was observed in the follicle cells.

Immunocytochemical localization of Bombyx-PTTH-like molecules in neurosecretory cells of the brain of the migratory locust, Locusta migratoria

SummaryUsing a monoclonal antibody directed against a synthetic pentadecapeptide corresponding to the N-terminus of the prothoracicotropic hormone (PTTH) of Bombyx mori, we report the presence of immunoreactive molecules in a large number of median neurosecretory cells of the pars intercerebralis of the migratory locust, Locusta migratoria. These cells correspond to the A1 cell type which we show to contain also neuroparsins, a family of predominant neurohormones of the migratory locust. In contrast, PTTH-like molecules are absent from A2 cells of the pars intercerebralis which contain Locusta insulin-related peptide (LIRP). Developmental studies show the presence of PTTH-related substances in neurosecretory cells of Locusta migratoria from late embryogenesis to adult development, including ageing vitellogenic female adults.

Endocrine control by neurosecretory cells of the pars intercerebralis and the corpora allata during the earlier phases of vitellogenesis in Locusta migratoria migratorioides R and F (Orthoptera)

Abstract In the adult female Locusta migratoria , the neurosecretory cells (A,B,C) of the pars intercerebralis and the corpora allata are essential for the onset of the second phase of vitellogenesis, which is characterized by the uptake of yolk proteins by the oocyte. Electrocoagulation of the neurosecretory cells inhibits vitellogenesis only if this operation is performed during the first five days of adult life (oocyte length from 0.4 to 1 mm). On the other hand, the presence of the corpora allata is essential for vitellogenesis until the beginning of the second phase of vitellogenesis (oocyte length from 0.4 to 4 mm). Implantation of one pair of corpora allata or an injection of juvenile hormone (JH) (10 μg per insect; JH 1 , C 18 ) in allatectomized females at first stimulates the differentiation of the follicular cells, which occurs normally during the first phase of vitellogenesis; the different structures observed in such oocytes are the same as in untreated insects.

L'action exercée par l'appareil endocrine sur les phases tardives de l'ovogenèse chez Locusta migratoria

Most studies dealing with the endocrine control of oogenesis are focused on vitellogenesis, but the later events of oogenesis: vitelline membrane formation and choriogenesis have received less atention. In Locusta migratoria, the corpora allata evidently control vitellogenesis, but seem to have no bearing upon the formation of the vitelline membrane or the chorion. If the insects are deprived of their CA at the time when the oocyte length is around 3.5 to 4 mm, (normal length at egg laying: 6.5 mm) vitelline membrane formation and the chorion production are unaffected. In the same species, the electrocoagulation of the pars intercerebralis or excision of corpora cardiaca disturb oogenesis; vitelline membrane material is synthesized and secreted, but the primary granules fail to join each other and to transform into vitelline membrane and the production of chorionic material is disturbed. The rER of the follicle cell seems quite active but the substance elaborated accumulates in the Golgi saccules, and therefore the cytoplasm contains only very few secretory granules. The implantation of supernumerary pars intercerebralis and corpora cardiaca into immature females induces precocious deposition of the vitelline membrane which is complete in 5.0 mm oocytes (instead of 5.6 to 6.0 mm) and chorion formation is completed in 5.5 mm oocytes (instead of 6.0 to 6.3 mm). Ecdysone is secreted in the ovaries at the end of oogenesis. We tested the result of injecting ecdysone to immature females. It results in hastening oocyte growth during 24 hr, but this accelerated growth is followed by degeneration.

Control of haemolymph protein synthesis and oocyte maturation by the corpora allata in female adults of Locusta migratoria (Orthoptera): Role of the blood-forming tissue

Abstract Oocyte growth in Locusta migratoria is divided into three major periods: previtellogenesis (oocyte length less than 0.8 mm; days 1–7 of adult life); subphase I of vitellogenesis (oocyte length between 0.8 and 2 mm; days 7–10 of adult life), and subphase II of vitellogenesis (oocyte length greater than 2 mm; day 10 of adult life till egg-laying). Subphase I of vitellogenesis is characterized by a marked increase in total hemolymph proteins. Both oocyte growth and hemolymph protein synthesis are known to be controlled by the corpora allata, the activity of which is very high only during subphase I of vitellogenesis. In addition, this subphase corresponds to a markedly increased activity of the hemocytopoietic tissue, resulting in a rise in the number of highly differentiated hemocytes in the blood. Selective X-irradiations of the hemocytopoietic tissue (pericardial region of the abdomen) affect both oocyte growth and hemolymph protein synthesis if they are performed during subphase I of vitellogenesis (time of highest activity of the corpora allata). The effects of these irradiations on both parameters are very similar to those of allatectomy. Sham-irradiations of other abdominal regions of equivalent surface affect neither oocyte growth nor hemolymph protein synthesis. It is therefore suggested that radiosensitive cells of the hemocytopoietic tissue elaborate one or several factors necessary for the transport and/or the mode of action of the corpora allata hormone.