Isolation of genes induced in Naegleria fowleriduring mouse brain passage

Abstract

We have isolated genes that are differentially expressed between Naegleria fowleri and N. gruberi by reverse dot blot analysis. Northern blot hybridization was applied to compare the expression patterns of the isolated genes before and after restoration of virulence by mouse brain passage of N. fowleri. Four hundred and eighty randomly selected cDNA clones of N. fowleri were hybridized with single-stranded cDNA probes of N. fowleri or N. gruberi. Among them, thirty-two clones showed a different signal between the two species. We determined the nucleotide sequences of twenty-two clones that displayed stronger hybridization with cDNA probes of N. fowleri than of N. gruberi. Only six clones provided useful information on their putative functions by sequence homology search through public databases. Four of them, showing a constant level of expression during mouse brain passage, encoded ribosomal protein, fumarase, malate dehydrogenase, or ubiquitin. The remaining two clones were homologous to genes for the high mobility group (HMG) protein and the 26S proteasome subunit. Interestingly, the expressions of these two genes were increased by successive mouse brain passages of N. fowleri. These results suggested that the HMG protein and 26S proteasome of N. fowleri may be involved in some biological processes to adapt the amoeba as a pathogen to the host.