A cDNA macroarray approach to parasite-induced gene expression changes in a songbird host:: genetic response of house finches to experimental infection by Mycoplasma gallisepticum

In 1994, the bacterial parasite Mycoplasma gallisepticum expanded its host range and swept through populations of a novel host - eastern US populations of the house finch (Carpodacus mexicanus). This epizootic caused a dramatic decline in finch population numbers, has been shown to have caused strong selection on house finch morphology, and presumably caused evolutionary change at the molecular level as finches evolved enhanced resistance. As a first step toward identifying finch genes that respond to infection by Mycoplasma and which may have experienced natural selection by this parasite, we used suppression subtractive hybridization (SSH) and cDNA macroarray approaches to identify differentially expressed genes regulated by the Mycoplasma parasite. Two subtractive cDNA libraries consisting of 16 512 clones were developed from spleen using an experimentally uninfected bird as the 'tester' and an infected bird as 'driver', and vice versa. Two hundred and twenty cDNA clones corresponding 34 genes with known vertebrate homologues and a large number of novel transcripts were found to be qualitatively up- or down-regulated genes by high-density filter hybridization. These gene expression changes were further confirmed by a high throughout reverse Northern blot approach and in specific cases by targeted Northern analysis. BLAST searches show that heat shock protein (HSP) 90, MHC II-associated invariant chain (CD74), T-cell immunoglobulin mucin 1 (TIM1), as well as numerous novel expressed genes not found in the databases were up- or down-regulated by the host in response to this parasite. Our results and macroarray resources provide a foundation for molecular co-evolutionary studies of the Mycoplasma parasite and its recently colonized avian host.