Anopheles gambiae is the principal vector of malaria, a disease that afflicts more than 500 million people and causes more than 1 million deaths each year. Tenfold shotgun sequence coverage was obtained from the PEST strain of A. gambiae and assembled into scaffolds that span 278 million base pairs. A total of 91% of the genome was organized in 303 scaffolds; the largest scaffold was 23.1 million base pairs. There was substantial genetic variation within this strain, and the apparent existence of two haplotypes of approximately equal frequency ("dual haplotypes") in a substantial fraction of the genome likely reflects the outbred nature of the PEST strain. The sequence produced a conservative inference of more than 400,000 single-nucleotide polymorphisms that showed a markedly bimodal density distribution. Analysis of the genome sequence revealed strong evidence for about 14,000 protein-encoding transcripts. Prominent expansions in specific families of proteins likely involved in cell adhesion and immunity were noted. An expressed sequence tag analysis of genes regulated by blood feeding provided insights into the physiological adaptations of a hematophagous insect.
The high degree of similarity between the mouse and human genomes is demonstrated through analysis of the sequence of mouse chromosome 16 (Mmu 16), which was obtained as part of a whole-genome shotgun assembly of the mouse genome. The mouse genome is about 10% smaller than the human genome, owing to a lower repetitive DNA content. Comparison of the structure and protein-coding potential of Mmu 16 with that of the homologous segments of the human genome identifies regions of conserved synteny with human chromosomes (Hsa) 3, 8, 12, 16, 21, and 22. Gene content and order are highly conserved between Mmu 16 and the syntenic blocks of the human genome. Of the 731 predicted genes on Mmu 16, 509 align with orthologs on the corresponding portions of the human genome, 44 are likely paralogous to these genes, and 164 genes have homologs elsewhere in the human genome; there are 14 genes for which we could find no human counterpart.
Paraoxon and chlorpyrifos-oxon, the active metabolites of the organophosphorus insecticides parathion and chlorpyrifos, respectively, are hydrolyzed by an "A"-esterase, paraoxonase, which is present in the sera of several mammalian species. In this study, we investigated whether levels of serum paraoxonase activity in laboratory animals can influence the in vivo toxicity of paraoxon and chlorpyrifos-oxon. Paraoxonase was found to be 7-fold higher in rabbit serum than in rat serum. The dose of paraoxon required to produce similar signs of toxicity and similar degrees of cholinesterase inhibition in rats and rabbits (0.5 and 2.0 mg/kg, respectively) differed by 4-fold. Paraoxonase was then purified from rabbit serum and 8.35 units was injected in the tail veins of rats, increasing the peak hydrolytic activity of rat serum by 9-fold toward paraoxon and by 50-fold toward chlorpyrifos-oxon. The increase in serum paraoxonase/chlorpyrifos-oxonase activity was long-lasting, with a 2- and 10-fold increase, respectively, still present after 24 hr. Thirty minutes following enzyme injection, rats were challenged with an acute dose of paraoxon or chlorpyrifos-oxon given by the intravenous, intraperitoneal, dermal, or oral route. Cholinesterase activities were measured in plasma, red blood cells, brain, and diaphragm after 4 hr. Rats pretreated with paraoxonase exhibited less inhibition of cholinesterase than vehicle-treated controls following identical doses of paraoxon, particularly when the organophosphate was given iv or dermally. A very high degree of protection, particularly toward brain and diaphragm cholinesterase, was provided by paraoxonase pretreatment in animals challenged with chlorpyrifos-oxon by all routes. These results indicate that levels of serum paraoxonase activity can affect the toxicity of paraoxon and chlorpyrifos-oxon.
Title: Spatial memory impairment and central muscarinic receptor loss following prolonged treatment with organophosphates McDonald BE, Costa LG, Murphy SD Ref: Toxicol Lett, 40:42, 1988 : PubMed
Memory impairment is one of the recurrent complaints of agricultural workers repeatedly exposed to organophosphorus insecticides. In an effort to establish an animal model for such behavioral effects, which would allow studying its underlying biochemical mechanism(s), in this study we evaluated spatial memory in animals following repeated organophosphate exposure. Male Long-Evans rats were given daily i.p. injections of either diisopropylfluorophosphate (DFP; 1 mg/kg/day) or disulfoton (O,O-diethyl S-[2-(ethylthio)ethyl] phosphorodithioate; 2 mg/kg/day) for 14 days. Acetylcholinesterase activity was inhibited 71-77% in the cortex, hippocampus, and striatum of rats treated with DFP, and 73-74% in those treated with disulfoton. Binding of [3H]quinuclidinyl benzilate ([3H]QNB) to cholinergic muscarinic receptors in the same brain areas was reduced 16-28% in organophosphate-treated rats. This decrease was due to a reduction in muscarinic receptor density (Bmax) with no changes in receptor affinity. At the end of the treatment rats were tested for spatial memory using the spontaneous alternation task in a T-maze. Rates of true spontaneous alternation were 64.4, 45.0, and 44.8% in animals which received corn oil, DFP, or disulfoton, respectively (P less than 0.05). These results indicate that prolonged inhibition of acetylcholinesterase caused by repeated organophosphate exposure alters spatial memory functions in rats, as well as causing a loss of muscarinic receptors. Considering the role of the cholinergic system in cognitive processes, these biochemical alterations could be related to the observed behavioral changes and may offer a potential explanation of the memory impairment reported by workers chronically exposed to organophosphates.
Title: Kinetic analysis of species difference in acetylcholinesterase sensitivity to organophosphate insecticides Wang C, Murphy SD Ref: Toxicol Appl Pharmacol, 66:409, 1982 : PubMed
Title: Malathion inhibition of esterases as a determinant of malathion toxicity Murphy SD Ref: Journal of Pharmacology & Experimental Therapeutics, 156:352, 1967 : PubMed
Title: The influence of various factors on the enzymatic conversion of organic thiophosphates to anticholinesterase agents Murphy SD, Dubois KP Ref: Journal of Pharmacology & Experimental Therapeutics, 124:194, 1958 : PubMed
Title: Quantitative measurement of inhibition of the enzymatic detoxification of malathion by EPN Murphy SD, Dubois KP Ref: Proceedings of the Society for Experimental Biology & Medicine, 96:813, 1957 : PubMed
Title: Toxicity and mechanism of action of some metabolites of Systox Dubois KP, Murphy SD, Thursh DR, Jr. Ref: AMA Arch Ind Health, 13:606, 1956 : PubMed
