René Lanot

Treatment of l(2)mbn Drosophila tumorous blood cells with the steroid hormone ecdysone amplifies the inducibility of antimicrobial peptide gene expression

Insects rely on both humoral and cellular mechanisms to defend themselves against microbial infections. The humoral response involves synthesis of a battery of potent antimicrobial peptides by the fat body and, to a lesser extent, by blood cells. The cellular response on the other hand consists of phagocytosis of small microorganisms and melanization and encapsulation of larger parasites. The l(2)mbn cell line, established from tumorous larval hemocytes, represents a system of choice to dissect the molecular events controlling cellular immunity. We report here that l(2)mbn cells can be efficiently induced to differentiate in adherent, macrophage-like cells by treatment with 20-hydroxyecdysone. Ecdysone treatment increases both the phagocytic capacity of l(2)mbn cells and their competence to express antimicrobial genes in response to immune challenge. We also report that expression of several regulatory molecules thought to be involved in the immune response is up-regulated by ecdysone in l(2)mbn cells.

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.

Conversion of a radiolabelled ecdysone precursor, 2,22,25-trideoxyecdysone, by embryonic and larval tissues of Locusta migratoria

A high specific activity tritiated ecdysone precursor, 2,22,25-trideoxyecdysone, was used to probe the capacity of various embryonic and larval tissues to perform the last 3 hydroxylation steps in ecdysone biosynthesis. Embryos at early stages of development, prior to the differentiation of their endocrine glands and embryonic heads, thoraces and abdomens of later stages, were found to have the capacity to hydroxylate the precursor to ecdysone. Larval epidermis and fat body are also able to transform 2,22,25-trideoxyecdysone into ecdysone; Malpighian tubules and midgut hydroxylate the precursor at C-2 but are apparently unable to hydroxylate both at C-22 and C-25. Larval prothoracic glands convert the precursor to ecdysone at a very efficient rate, which is 1-2 magnitudes higher than that of the other tissues investigated; several data argue for the existence of a privileged sequence of hydroxylations, C-25, C-22, C-2, in the larval prothoracic glands.

Further experimental evidence for the involvement of ecdysone in the control of meiotic reinitiation in oocytes of Locusta migratoria (Insecta, Orthoptera)

Ecdysone has recently been shown to be able to trigger meiotic reinitiation in vitro in submature oocytes of Locusta. In the present study we have experimentally depressed (by 60-70%) ecdysone biosynthesis in the ovaries of adult females by rearing them on a diet with a modified sterol profile. Mature oocytes from such females fail to undergo normal reinitiation, but when incubated in vitro, can be induced to break their meiotic arrest by the addition of exogenous ecdysone. These results lend further support to the hypothesis that in Locusta, ovarian ecdysone is involved in the control of meiotic reinitiation.

Ecdysteroids and meiotic reinitiation in Palaemon serratus (Crustacea Decapoda Natantia) and in Locusta migratoria (Insecta orthoptera). A comparative study

Summary Meiotic reinitiation has been studied in Locusta migratoria and Palaemon serratus in relation to the titre of free ecdysteroids present in the maturing oocyte. In both species meiotic reinitiation is characterized by two meiotic arrests, in prophase I and in metaphase I, and the first meiotic resumption which leads to germinal vesicle breakdown (GVBD) is correlated with increasing titres of ecdysteroids in the oocyte. Meiotic reinitiation has been successfully triggered in the oocytes of both species by incubation with physiological doses of ecdysteroids.

Ecdysteroids and meiotic reinitiation in oocytes of Periplaneta americana (Dictyoptera) and Gryllus bimaculatus (Orthoptera)

Summary The role of ecdysteroids in meiotic reinitiation has been studied in oocytes of Periplaneta americana and of Gryllus bimaculatus. In the oocyte of Periplaneta the concentration of free ecdysteroids increases markedly during the period which precedes chorionation, and meiosis resumes some hours later, germinal vesicle breakdown (GVBD) occurring at the time of ovulation. In the oocyte of Gryllus a similar accumulation of ecdysteroids has been observed prior to GVBD which occurs before ovulation. Meiotic reinitiation could be triggered in the vitellogenic oocyte of both species by in vitro application of exogenous ecdysone.