In Vitro Cellular Division of Trypanosoma abeli Reveals Two Pathways for Organelle Replication

Abstract

Since the observation of the great pleomorphism of fish trypanosomes, in vitro culture has become an important tool to support taxonomic studies investigating the biology of cultured parasites, such as their structure, growth dynamics, and cellular cycle. Relative to their biology, ex vivo and in vitro studies have shown that these parasites, during the multiplication process, duplicate and segregate the kinetoplast before nucleus replication and division. However, the inverse sequence (the nucleus divides before the kinetoplast) has only been documented for a species of marine fish trypanosomes on a single occasion. Now, this previously rare event was observed in Trypanosoma abeli, a freshwater fish trypanosome. Specifically, from 376 cultured parasites in the multiplication process, we determined the sequence of organelle division for 111 forms; 39% exhibited nucleus duplication prior to kinetoplast replication. Thus, our results suggest that nucleus division before the kinetoplast may not represent an accidental or erroneous event occurring in the main pathway of parasite reproduction, but instead could be a species-specific process of cell biology in trypanosomes, such as previously noticed for Leishmania. This "alternative" pathway for organelle replication is a new field to be explored concerning the biology of marine and freshwater fish trypanosomes.

Coordination of the Cell Cycle in Trypanosomes

“…G 2 to the start of mitosis involves the cyclin B-like cyclins CYC6 and CYC8 (46,53,84) and the kinases CRK3 (CDK1-like) and CRK9 (33, 149) (Figure 3b). Mitosis has a dependency on nuclear S phase but appears independent of kinetoplast S phase and cytoskeletal events, and its timing can vary: It occurs after kinetoplast division in T. brucei and Trypanosoma cruzi epimastigotes (36), during kinetoplast division in Leishmania (8,139), and apparently at a variable time relative to kinetoplast division in Trypanosoma abeli (17). The closed mitotic spindle is a conventional microtubule-based structure (98).…”