To investigate the effects of fluorosis on development and gene expression profiles of silkworm, highly resistant silkworm strain 441, and highly susceptible silkworm strain 440 were treated with 200 ppm fluoride (designated as 440F and 441 F) and water (designated as 440DZ and 441DZ). Fluorotic silkworm showed body color and behavior changes. Statistical analysis indicated that growth index of 440F was lower than 440DZ, 441DZ, and 441F. The mortality of 440F was higher than others. Fluorescent differential display enabled us to obtain a differentially expressed cDNA. Bioinformatics analyses indicated that it belonged to cytochrome P450 family, denoted Bmcyp306a1, which contained seven exons and six introns. Phylogenetic tree showed BmCYP306A1 had high homology with Manduca sexta' P450 protein. Expression analysis indicated that Bmcyp306a1 was exclusively expressed in 441DZ and 441F and was down-regulated under fluoride treatment. The tissue-specific expression indicated Bmcyp306a1 had high-expression level in midgut and ovary in 441F. The data revealed that there was obvious dose-effect and times relationship with the pathological changes and gene expression. Expression profiles of Bmcyp306a1 suggested that P450 gene was crucial to physiological modification and might be involved in fluoride resistance. (C) 2008 Elsevier B.V. All rights reserved.