TRACK is a protein with sequence similarity to mammalian RACK1 and yeast Cpc2. This family of proteins is predicted to fold into a 7-bladed beta propeller based upon similarities to G-beta. TRACK is able to restore growth and morphology to yeast cpc2 null mutants.

Watch the Movie

To test the hypothesis that TRACK is involved in signal processes in Trypanosoma brucei, the cellular content of TRACK was depleted with RNAi. The following movie shows procyclic cells that have been induced with tetracycline for 4 days, at which time western blots show that TRACK is not detectable in the cells.

The movie shows the formation of spicules at the posterior end of the cell and cells that fail to complete the process of cytokinesis. Cells continue to undergo multiple rounds of partial cell division. Each partial division occurs non-synchronously, even though considerable cytoplasm is shared between the "daughter cells". This point becomes clear towards the end of the movie when cells with odd-numbers of cytoplasmic extensions are seen. The fact that cells are viable through multiple rounds of partial division suggests that TRACK is not essential for other key processes in these cells. Moreover, these are the first observations to indicate that cytokinesis, once initiated is disjoint in trypanosomes. Protein(s) are required for mid-stage progression that are not necessary for the initiation stage of this process.

Larry Ruben
lruben@mail.smu.edu