Characterization of a Netrin-4 Like Protein in \u3cem\u3eTetrahymena thermophila\u3c/em\u3e

The netrin family of proteins has homeostatic roles in vertebrate development and angiogenesis, and pathophysiological roles in the progression and metastasis of cancer. We have previously characterized a netrin-1-like protein in Tetrahymena thermophila, and have shown that vertebrate netrin-1, netrin-3, and netrin-4 all serve as chemorepellents in this organism. We are currently using Western blotting and immunofluorescence to further characterize the netrin-like proteins in Tetrahymena. Western blotting with our anti-netrin-4 antibody shows a band that is clearly visible in whole cell extract, but shows little reactivity with secreted protein, indicating that most of our netrin-4-like protein remains within the cell. Western blotting of whole cell extract with anti-netrin-1, netrin-3, and netrin-4 antibodies shows a clear band measuring 50 kD that stains with all three antibodies. Some lower molecular weight bands are also evident in all three blots, possibly due to proteolytic activity. Immunolocalization with an anti-netrin-4 antibody shows some colocalization with netrin-1, netrin-3, and ER Tracker™. Our anti-netrin-4 antibody localizes to the oral groove, basal bodies, and nuclei of cells, indicating a possible structural role for the netrin-4-like protein in this organism. Further research will involve determining the primary amino acid sequence of the 50 kD protein and comparing it with the Tetrahymena thermophila proteome database to help ascertain the physiological role of this protein

How does vegetation affect sedimentation on tidal marshes? Investigating particle capture and hydrodynamic controls on biologically mediated sedimentation

Plants are known to enhance sedimentation on intertidal marshes. It is unclear, however, if the dominant mechanism of enhanced sedimentation is direct organic sedimentation, particle capture by plant stems, or enhanced settling due to a reduction in turbulent kinetic energy within flows through the plant canopy. Here we combine several previously reported laboratory studies with an 18 year record of salt marsh macrophyte characteristics to quantify these mechanisms. In dense stands of Spartina alterniflora (with projected plant areas per unit volume of >10 m 121) and rapid flows (>0.4 m s 121), we find that the fraction of sedimentation from particle capture can instantaneously exceed 70%. In most marshes dominated by Spartina alterniflora, however, we find particle settling, rather than capture, will account for the majority of inorganic sedimentation. We examine a previously reported 2 mm yr 121 increase in accretion rate following a fertilization experiment in South Carolina. Prior studies at the site have ruled out organic sedimentation as the cause of this increased accretion. We apply our newly developed models of particle capture and effective settling velocity to the fertilized and control sites and find that virtually all (>99%) of the increase in accretion rates can be attributed to enhanced settling brought about by reduced turbulent kinetic energy in the fertilized canopy. Our newly developed models of biologically mediated sedimentation are broadly applicable and can be applied to marshes where data relating biomass to stem diameter and projected plant area are available