Differential transcript expression between the microfilariae of the filarial nematodes, Brugia malayi and B. pahangi

Brugia malayi and B. pahangi are two closely related nematodes that cause filariasis in humans and animals. However, B. pahangi microfilariae are able to develop in and be transmitted by the mosquito, Armigeres subalbatus, whereas most B. malayi are rapidly melanized and destroyed within the mosquito hemocoel. A cross-species microarray analysis employing the B. malayi V2 array was carried out to determine the transcriptional differences between B. malayi and B. pahangi microfilariae with similar age distribution.

Following microarray data analysis, a list of preferentially expressed genes in both microfilariae species was generated with a false discovery rate estimate of 5% and a signal intensity ratio of 2 or higher in either species. A total of 308 probes were preferentially expressed in both species with 149 probes, representing 123 genes, in B. pahangi microfilariae and 159 probes, representing 107 genes, in B. malayi microfilariae. In B. pahangi, there were 76 (62%) up-regulated transcripts that coded for known proteins that mapped into the KEGG pathway compared to 61 (57%) transcripts in B. malayi microfilariae. The remaining 47 (38%) transcripts in B. pahangi and 46 (43%) transcripts in B. malayi microfilariae were comprised almost entirely of hypothetical genes of unknown function. Twenty-seven of the transcripts in B. pahangi microfilariae coded for proteins that associate with the secretory pathway compared to thirty-nine in B. malayi microfilariae. The data obtained from real-time PCR analysis of ten genes selected from the microarray list of preferentially expressed genes showed good concordance with the microarray data, indicating that the microarray data were reproducible.

In this study, we identified gene transcripts that were preferentially expressed in the microfilariae of B. pahangi and B. malayi, some of which coded for known immunomodulatory proteins. These comparative transcriptome data will be of interest to researchers keen on understanding the inherent differences, at the molecular level, between B. malayi and B. pahangi microfilariae especially because these microfilariae are capable of surviving in the same vertebrate host but elicit different immune response outcomes in the mosquito, Ar. subalbatus.