Cell cycle of Trypanosoma epinepheli bloodstream forms in vivo and in vitro.

Trypanosomes constitute a group of hemoflagellates that can infect many vertebrate species ranging from fish to humans. Most of the detailed studies are focused on mammalian trypanosomes of medical and veterinary importance. Although variations in cell cycle progression have been elucidated in mammalian trypanosomes, details of these processes remain elusive in other vertebrate trypanosomes. To address this, we established an in vitro culture and an in vivo fish model in tilapia to understand the cell morphology and cell division events of Trypanosoma epinepheli. The doubling time of T. epinepheli in vivo and cultured in vitro were 10.8 hours and 31.1 hours, respectively. We observed that the segregation movement of the kinetoplast and nucleus in T. epinepheli is distinct from mammalian trypanosomes but similar to that, previously described, for Trypanosoma carassii. Also, growth and shortening of the flagellum is coordinated with cell cycle phases. Finally, the detailed timing of cell cycle phases was determined by morphology and PI-stained flow cytometry and includes the G1, S, G2, M, division (D) and post-division (A) phases for the nucleus and/or kinetoplast, as well as the cytokinesis (C) phase. These findings shed light on the potential strategies for completing the cell division process and may facilitate future research on marine trypanosomes.