RESUMO
The GAL4/UAS system has been extensively employed in Drosophila to control gene expression in defined spatial patterns. More recently this system has been successfully applied to express genes involved in neurodegeneration to model various diseases in the fruit fly. We used transgenic lines expressing different levels of GAL4 in a particular subset of neurons involved in the control of rhythmic behaviour, so that its impact on neuronal physiology would result in altered locomotor activity, which could be readily assessed. We observed a striking correlation between gal4 dosage and behavioural defects associated with apoptotic neuronal loss in the specific GAL4-expressing neurons. Increased gal4 dosage correlated with accumulation of insoluble GAL4, suggesting that the cascade of events leading to apoptosis might be triggered by protein deposits of either GAL4 or protein intermediates. Behavioural defects were rescued by expression of hsp70, a classic chaperone that also interferes with cell death pathways. In agreement with the latter, the viral caspase inhibitor p35 also rescued GAL4-induced behavioural defects. Our observations demonstrate the intrinsic effects of GAL4 deregulation on neuronal viability and suggest that an excess of GAL4 might enhance neuronal deficits observed in models of neurodegeneration.
Assuntos
Apoptose/fisiologia , Degeneração Neural/fisiopatologia , Neurônios/patologia , Proteínas de Saccharomyces cerevisiae/metabolismo , Fatores de Transcrição/metabolismo , Transgenes/fisiologia , Animais , Animais Geneticamente Modificados , Sobrevivência Celular/fisiologia , Proteínas de Ligação a DNA , Drosophila , Dosagem de Genes/fisiologia , Regulação da Expressão Gênica , Marcação In Situ das Extremidades Cortadas , Larva/fisiologia , Masculino , Microscopia Eletrônica de Varredura , Atividade Motora/fisiologia , Degeneração Neural/metabolismo , Degeneração Neural/patologia , Neurônios/fisiologia , Fenótipo , Células Fotorreceptoras de Invertebrados/fisiologia , Células Fotorreceptoras de Invertebrados/ultraestrutura , Proteínas de Saccharomyces cerevisiae/genética , Fatores de Transcrição/genéticaRESUMO
To further understand the function of morphogenetic hormones in honeybee eye differentiation, the alterations in ommatidial patterning induced by pyriproxyfen, a juvenile hormone (JH) analogue, were studied by scanning and transmission electron microscopy. Prepupae of prospective honeybee workers were treated with pyriproxyfen and the effects on ommatidial differentiation were described at the end of the pupal development. The results show that the entire ommatidia, i.e., the dioptric as well as the receptor systems, were affected by the JH analogue. The wave of ommatidial differentiation, which progresses from the posterior to the anterior region of the pupal eyes, was arrested. In treated pupae, the rhabdomeres only differentiated at the apical axis of the retinula, the secondary and tertiary pigment cells did not develop their cytoplasm protrusions, and the cone cell quartet did not pattern correctly. Simultaneously, an intense vacuolization was observed in cells forming ommatidia. In a previous study we showed that pyriproxyfen exerts an inhibition on pupal ecdysteroid secretion. In this sense, the arrested ommatidial differentiation in pyriproxyfen-treated pupae could be due to a secondary effect resulting from an alteration in pupal ecdysteroid titers.