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Background: Brugia malayi is a nematode parasite that causes lymphatic filariasis, a disfiguring and disabiling tropical disease. Although a first draft genome sequence was released in 2007, very little is understood about transcription programs that govern developmental changes required for the parasite's development and survival in its mammalian and insect hosts., Results: We used a microarray with probes that represent some 85% of predicted genes to generate gene expression profiles for seven parasite life cycle stages/sexes. Approximately 41% of transcripts with detectable expression signals were differentially expressed across lifecycle stages. Twenty-six percent of transcripts were exclusively expressed in a single parasite stage, and 27% were expressed in all stages studied. K-means clustering of differentially expressed transcripts revealed five major transcription patterns that were associated with parasite lifecycle stages or gender. Examination of known stage-associated transcripts validated these data sets and suggested that newly identified stage or gender-associated transcripts may exercise biological functions in development and reproduction. The results also indicate that genes with similar transcription patterns were often involved in similar functions or cellular processes. For example, nuclear receptor family gene transcripts were upregulated in gene expression pattern four (female-enriched) while protein kinase gene family transcripts were upregulated in expression pattern five (male-enriched). We also used pair-wise comparisons to identify transcriptional changes between life cycle stages and sexes., Conclusions: Analysis of gene expression patterns of lifecycle in B. malayi has provided novel insights into the biology of filarial parasites. Proteins encoded by stage-associated and/or stage-specific transcripts are likely to be critically important for key parasite functions such as establishment and maintenance of infection, development, reproduction, and survival in the host. Some of these may be useful targets for vaccines or new drug treatments for filariasis.

Background: Many species of filarial nematodes depend on Wolbachia endobacteria to carry out their life cycle. Other species are naturally Wolbachia-free. The biological mechanisms underpinning Wolbachia-dependence and independence in filarial nematodes are not known. Previous studies have indicated that Wolbachia have an impact on mitochondrial gene expression, which may suggest a role in energy metabolism. If Wolbachia can supplement host energy metabolism, reduced mitochondrial function in infected filarial species may account for Wolbachia-dependence. Wolbachia also have a strong influence on mitochondrial evolution due to vertical co-transmission. This could drive alterations in mitochondrial genome sequence in infected species. Comparisons between the mitochondrial genome sequences of Wolbachia-dependent and independent filarial worms may reveal differences indicative of altered mitochondrial function., Results: The mitochondrial genomes of 5 species of filarial nematodes, Acanthocheilonema viteae, Chandlerella quiscali, Loa loa, Onchocerca flexuosa, and Wuchereria bancrofti, were sequenced, annotated and compared with available mitochondrial genome sequences from Brugia malayi, Dirofilaria immitis, Onchocerca volvulus and Setaria digitata. B. malayi, D. immitis, O. volvulus and W. bancrofti are Wolbachia-dependent while A. viteae, C. quiscali, L. loa, O. flexuosa and S. digitata are Wolbachia-free. The 9 mitochondrial genomes were similar in size and AT content and encoded the same 12 protein-coding genes, 22 tRNAs and 2 rRNAs. Synteny was perfectly preserved in all species except C. quiscali, which had a different order for 5 tRNA genes. Protein-coding genes were expressed at the RNA level in all examined species. In phylogenetic trees based on mitochondrial protein-coding sequences, species did not cluster according to Wolbachia dependence., Conclusions: Thus far, no discernable differences were detected between the mitochondrial genome sequences of Wolbachia-dependent and independent species. Additional research will be needed to determine whether mitochondria from Wolbachia-dependent filarial species show reduced function in comparison to the mitochondria of Wolbachia-independent species despite their sequence-level similarities.