ABSTRACT
Left-right asymmetries in the epithalamic region of the brain are widespread across vertebrates, but their magnitude and laterality varies among species. Whether these differences reflect independent origins of forebrain asymmetries or taxa-specific diversifications of an ancient vertebrate feature remains unknown. Here we show that the catshark Scyliorhinus canicula and the lampreys Petromyzon marinus and Lampetra planeri exhibit conserved molecular asymmetries between the left and right developing habenulae. Long-term pharmacological treatments in these species show that nodal signalling is essential to their generation, rather than their directionality as in teleosts. Moreover, in contrast to zebrafish, habenular left-right differences are observed in the absence of overt asymmetry of the adjacent pineal field. These data support an ancient origin of epithalamic asymmetry, and suggest that a nodal-dependent asymmetry programme operated in the forebrain of ancestral vertebrates before evolving into a variable trait in bony fish.
Subject(s)
Functional Laterality/genetics , Gene Expression Regulation, Developmental , Nodal Signaling Ligands/genetics , Petromyzon/genetics , Prosencephalon/embryology , Sharks/genetics , Animals , Base Sequence , Diencephalon/embryology , Diencephalon/metabolism , Embryo, Nonmammalian , Fibroblast Growth Factors/genetics , Fibroblast Growth Factors/metabolism , Homeodomain Proteins/genetics , Homeodomain Proteins/metabolism , Lampreys/genetics , Left-Right Determination Factors/genetics , Left-Right Determination Factors/metabolism , Molecular Sequence Data , Nodal Protein/genetics , Nodal Protein/metabolism , Nodal Signaling Ligands/metabolism , Prosencephalon/metabolism , Signal Transduction , Transforming Growth Factor beta/genetics , Transforming Growth Factor beta/metabolismABSTRACT
The herbicide bentazon (CASRN 25057-89-0) is extensively used in agriculture in Brittany (France) to replace atrazine. Bentazon is not readily adsorbed by soil and therefore it enters adjacent freshwater ecosystems, making its way to estuarine and marine waters areas. Information regarding its effects on marine ecosystems is scarce. Phytotoxicity assessments were conducted in the laboratory on the common diatom Chaetoceros gracilis using both the active ingredient and its formulated product (Basamaïs). The 3 day EC(50) using cell counts were, respectively, 150 mg/L and 60 microg/L for bentazon active ingredient and for bentazon-formulated while cellular volume was increased. Although bentazon is known as a photosystem II inhibitor, it produced an increase of pigment (chlorophylls a, c, and carotenoids) content, ATP synthesis, rates of photosynthesis and respiration, and TBARS formation. Therefore, pigments cannot be used as biomarkers of toxicity. Algal cell recovery from bentazon effects occurred after 6-9 days, suggesting a tolerance mechanism.
