Degradation of haloaromatic compounds

An ever increasing number of halogenated organic compounds has been produced by industry in the last few decades. These compounds are employed as biocides, for synthetic polymers, as solvents, and as synthetic intermediates. Production figures are often incomplete, and total production has frequently to be extrapolated from estimates for individual countries. Compounds of this type as a rule are highly persistent against biodegradation and belong, as "recalcitrant" chemicals, to the class of so-called xenobiotics. This term is used to characterise chemical substances which have no or limited structural analogy to natural compounds for which degradation pathways have evolved over billions of years. Xenobiotics frequently have some common features. e.g. high octanol/water partitioning coefficients and low water solubility which makes for a high accumulation ratio in the biosphere (bioaccumulation potential). Recalcitrant compounds therefore are found accumulated in mammals, especially in fat tissue, animal milk supplies and also in human milk. Highly sophisticated analytical techniques have been developed for the detection of organochlorines at the trace and ultratrace level

Silencing cuticular pigmentation genes enables RNA FISH in intact insect appendages

Optical imaging of gene expression by fluorescence in situ hybridisation (FISH) in insects is often impeded by their pigmented cuticle. Since most chemical bleaching agents are incompatible with FISH, we developed a RNA interference-based method for clearing cuticular pigmentation which enables using whole-mount body appendages for RNA FISH. Silencing laccase2 or tyrosine hydroxylase in two leaf beetles species (Chrysomela populi, Phaedon cochleariae) cleared their pigmented cuticle and decreased light absorbance. Subsequently, intact appendages (palps, antennae, legs) from RNAi-cleared individuals were used to image expression and spatial distribution of antisense mRNA of two chemosensory genes (gustatory receptor, odorant-binding protein). Imaging did neither work for RNAi-controls due to retained pigmentation, nor for FISH-controls (sense mRNA). Several bleaching agents were incompatible with FISH, either due to degradation of RNA, lack of clearing efficacy or long incubation times. Overall, silencing pigmentation genes is a significant improvement over bleaching agents enabling FISH in intact appendages