Netrin proteins are a family of laminin-related secreted proteins that provide signals for axonal growth and cell migration during vertebrate development. Netrin homologs are expressed throughout the animal kingdom; however, some animals do not express a homolog of any known netrin receptors. We have previously found that the ciliated protozoan, Tetrahymena thermophila, responds to netrin-1 peptide by showing avoidance behavior. In addition, Tetrahymena secrete a protein that is immunologically similar to netrin-1 as detected by ELISA. Since netrin-3, like netrin-1, is a guidance molecule for axons and overlaps signaling pathways with netrin-1 in vertebrates, we hypothesized that netrin-3 may also act as a chemorepellent in Tetrahymena. While behavioral assays did not confirm this hypothesis, growth assays indicate that netrin-3 peptide inhibits cell division in Tetrahymena. In addition, ELISA and Western blots indicate that a netrin-3 like protein of approximately 48 kDa is secreted from Tetrahymena. Immunolocalization of this protein within the cell shows that it appears in widely distributed throughout the cell, and co-localizes with the netrin-1 like protein. Using ER tracker™, we found that some of the netrin-3-like protein co-localizes with the endoplasmic reticulum, as might be expected for a secreted protein. Further experimentation is necessary to determine the mechanism by which netrin-3 peptide inhibits growth in Tetrahymena.
Available at: http://works.bepress.com/heather_kuruvilla/64/