Common and Distinct Roles of Juvenile Hormone Signaling Genes in Metamorphosis of Holometabolous and Hemimetabolous Insects

Insect larvae metamorphose to winged and reproductive adults either directly (hemimetaboly) or through an intermediary pupal stage (holometaboly). In either case juvenile hormone (JH) prevents metamorphosis until a larva has attained an appropriate phase of development. In holometabolous insects, JH acts through its putative receptor Methoprene-tolerant (Met) to regulate Krüppel-homolog 1 (Kr-h1) and Broad-Complex (BR-C) genes. While Met and Kr-h1 prevent precocious metamorphosis in pre-final larval instars, BR-C specifies the pupal stage. How JH signaling operates in hemimetabolous insects is poorly understood. Here, we compare the function of Met, Kr-h1 and BR-C genes in the two types of insects. Using systemic RNAi in the hemimetabolous true bug, Pyrrhocoris apterus, we show that Met conveys the JH signal to prevent premature metamorphosis by maintaining high expression of Kr-h1. Knockdown of either Met or Kr-h1 (but not of BR-C) in penultimate-instar Pyrrhocoris larvae causes precocious development of adult color pattern, wings and genitalia. A natural fall of Kr-h1 expression in the last larval instar normally permits adult development, and treatment with an exogenous JH mimic methoprene at this time requires both Met and Kr-h1 to block the adult program and induce an extra larval instar. Met and Kr-h1 therefore serve as JH-dependent repressors of deleterious precocious metamorphic changes in both hemimetabolous and holometabolous juveniles, whereas BR-C has been recruited for a new role in specifying the holometabolous pupa. These results show that despite considerable evolutionary distance, insects with diverse developmental strategies employ a common-core JH signaling pathway to commit to adult morphogenesis

Activation of c-Jun N-Terminal Kinase (JNK) during Mitosis in Retinal Progenitor Cells

Most studies of c-Jun N-terminal Kinase (JNK) activation in retinal tissue were done in the context of neurodegeneration. In this study, we investigated the behavior of JNK during mitosis of progenitor cells in the retina of newborn rats. Retinal explants from newborn rats were kept in vitro for 3 hours and under distinct treatments. Sections of retinal explants or freshly fixed retinal tissue were used to detect JNK phosphorylation by immunohistochemistry, and were examined through both fluorescence and confocal microscopy. Mitotic cells were identified by chromatin morphology, histone-H3 phosphorylation, and location in the retinal tissue. The subcellular localization of proteins was analyzed by double staining with both a DNA marker and an antibody to each protein. Phosphorylation of JNK was also examined by western blot. The results showed that in the retina of newborn rats (P1), JNK is phosphorylated during mitosis of progenitor cells, mainly during the early stages of mitosis. JNK1 and/or JNK2 were preferentially phosphorylated in mitotic cells. Inhibition of JNK induced cell cycle arrest, specifically in mitosis. Treatment with the JNK inhibitor decreased the number of cells in anaphase, but did not alter the number of cells in either prophase/prometaphase or metaphase. Moreover, cells with aberrant chromatin morphology were found after treatment with the JNK inhibitor. The data show, for the first time, that JNK is activated in mitotic progenitor cells of developing retinal tissue, suggesting a new role of JNK in the control of progenitor cell proliferation in the retina

A Drosophila Model for EGFR-Ras and PI3K-Dependent Human Glioma

Gliomas, the most common malignant tumors of the nervous system, frequently harbor mutations that activate the epidermal growth factor receptor (EGFR) and phosphatidylinositol-3 kinase (PI3K) signaling pathways. To investigate the genetic basis of this disease, we developed a glioma model in Drosophila. We found that constitutive coactivation of EGFR-Ras and PI3K pathways in Drosophila glia and glial precursors gives rise to neoplastic, invasive glial cells that create transplantable tumor-like growths, mimicking human glioma. Our model represents a robust organotypic and cell-type-specific Drosophila cancer model in which malignant cells are created by mutations in signature genes and pathways thought to be driving forces in a homologous human cancer. Genetic analyses demonstrated that EGFR and PI3K initiate malignant neoplastic transformation via a combinatorial genetic network composed primarily of other pathways commonly mutated or activated in human glioma, including the Tor, Myc, G1 Cyclins-Cdks, and Rb-E2F pathways. This network acts synergistically to coordinately stimulate cell cycle entry and progression, protein translation, and inappropriate cellular growth and migration. In particular, we found that the fly orthologs of CyclinE, Cdc25, and Myc are key rate-limiting genes required for glial neoplasia. Moreover, orthologs of Sin1, Rictor, and Cdk4 are genes required only for abnormal neoplastic glial proliferation but not for glial development. These and other genes within this network may represent important therapeutic targets in human glioma

Trichloroacetic acid in Norway spruce/soil-system. I. Biodegradation in soil.

Trichloroacetic acid (TCA) as a phytotoxic substance affects health status of coniferous trees. It is known as a secondary air pollutant (formed by photooxidation of tetrachloroethene and 1,1,1-trichloroethane) and as a product of chlorination of humic substances in soil. Its break-down in soil, however, influences considerably the TCA level, i.e. the extent of TCA uptake by spruce roots. In connection with our investigations of TCA effects on Norway spruce, microbial processes in soil were studied using 14C-labeling. It was shown that TCA degradation in soil is a fast process depending on TCA concentration, soil properties, humidity and temperature. As a result, the TCA level in soil is determined by a steady state between uptake from the atmosphere, formation in soil, leaching and degradation. The process of TCA degradation in soil thus participates significantly in the chlorine cycle in forest ecosystems

Biodegradation of trichloroacetic acid in Norway spruce/soil system.

Trichloroacetic acid (TCA) belongs to secondary atmospheric pollutants affecting the forest health. Distribution of [1,2-C-14]TCA-residues and TCA biodegradation were investigated in 4-year-old nursery-grown trees of Norway spruce [Picea abies (L.) Karat.] in the whole plant/soil system. Radioactivity was monitored in needles, wood, roots and soil as well as in the air. During two weeks of exposure TCA was continuously degraded, especially in the soil. Estimates of radioactivity balance showed loss of radioactivity into the atmosphere in the form of (CO2)-C-14; unincorporated [1,2-C-14]TCA, chloroform, carbon monoxide and methane were not detected at all. TCA degradation to CO2 was indicated also in the spruce needles. Moreover, it was found that soil litter contained [1,2-C-14]TCA unavailable to microorganisms