Gene expression of acetylcholinesterase in hybrid catfish (Clarias gariepinus X Clarias macrocephalus) exposed to chlorpyrifos and carbaryl.

After serving as an eurotransmitter, acetylcholine is hydrolyzed by acetylcholinesterase (AChE). Inhibition of AChE is considered to be a specific biomarker for exposure to organophosphate and carbamate insecticides. In this study the AChE gene was isolated from hybrid catfish brain by RT-PCR methods using degenerate primers. The amplified fragment of 966 nucleotides generated by PCR was cloned, and sequence analysis showed 82% nucleotide identity with AChE of the Electrophorus electricus. Specific primers of the hybrid catfish AChE gene were then synthesized and used in the examination of AChE gene expression in brain tissue of hybrid catfish exposed to sublethal concentrations of chlorpyrifos (0.43, 4.3 and 43 microM) and carbaryl (1.19, 11.9 and 119 microM) for 24 hr. Real-time PCR was used to compare with the amplified 28S rRNA gene. AChE gene expression was significantly elevated 12.4 times in catfish exposed to 43 microM chlorpyrifos in comparison to the control group (p<0.05). Carbaryl did not produce any significant change. These results indicate thatAChE is more sensitive to administration of chlorpyrifos than carbaryl. The induction of the AChE gene indicates the possibility of using this gene as biomarker for detecting effects of organophosphate insecticides in hybrid catfish.