Expression, localization and alternative function of cytoplasmic asparaginyl-tRNA synthetase in Brugia malayi

Aminoacyl-tRNA synthetases (AARS) are a family of enzymes that exhibit primary and various secondary functions in different species. In Brugia malayi, the gene for asparaginyl-tRNA synthetase (AsnRS), a class II AARS, previously has been identified as a multicopy gene encoding an immunodominant antigen in the serum of humans with lymphatic filariasis. However, the relative level of expression and alternative functions of AARS in nematode parasites is not well understood. We searched the Filarial Genome Project database to identify the number and amino acid specificity of B. malayi AARS cDNAs to gain insight into the role of different AARS in filaria. These data showed that cytoplasmic AsnRS was present in five gene clusters, and is the most frequently represented member of the aminoacyl-tRNA synthetase family in adult B. malayi. The relative level of AsnRS transcribed in adult female B. malayi was compared to the levels of a low abundance and medium abundance AARS by quantitative real-time RT-PCR. By this method, AsnRS cDNA was 11 times greater than arginyl-tRNA synthetase and methionyl-tRNA synthetase cDNA. In situ hybridization using a B. malayi AsnRS-specific oligonucleotide probe identified abundant cytoplasmic mRNA, particularly in the hypodermis of adult B. malayi. In the absence of tRNA, AsnRS synthesizes diadenosine triphosphate, a potent regulator of cell growth in other eukaryotes. These data support the hypothesis that all AARS are not equally expressed in B. malayi and that these enzymes may demonstrate important alternative functions in filaria.