The netrin family of proteins was first discovered because of their role in axonal guidance during development. Netrin homologues are important developmental signals in organisms ranging from vertebrates to the nematode, Caenorhabditis elegans, and netrin-like proteins have even been found in the ciliated protozoan, Tetrahymena thermophila. Since the lin-4 miRNA regulates netrin signaling in C. elegans, we hypothesized that a lin-4 homologue might exists in Tetrahymena thermophila. In order to test this hypothesis, we purified total miRNA from T. thermophila, used this miRNA to make cDNA, then used RT-PCR to quantitate the amount of lin-4 specific cDNA we obtained. Our sample was positive for total cDNA, but not for the lin-4 cDNA specifically, suggesting that this miRNA may not have a homologue in Tetrahymena
