Evolutionary cell biology of chromosome segregation
Co-workers: Olga Nerusheva, Gabriele Marcianò, Joris Treep, Hanako Hayashi, Midori Kanazawa
Faithful transmission of genetic material is essential for the survival of all organisms. Defects in this process lead to cancer or birth defects in humans. Elucidating the mechanism of chromosome segregation is therefore key to understanding the molecular basis of these diseases. Eukaryotic chromosome segregation is driven by the kinetochore that assembles onto centromeric DNA to capture spindle microtubules and govern the movement of chromosomes. Its molecular mechanism has been revealed from studies of conventional model eukaryotes, such as yeasts, worms, flies and human. However, these organisms are closely related in the evolutionary timescale and it therefore remained unclear whether all eukaryotes utilize a similar mechanism. The evolutionary origins of the segregation apparatus also remain enigmatic.
To gain insights into these questions, my group is studying Trypanosoma brucei, an experimentally-tractable kinetoplastid parasite that branched early in eukaryotic history. No canonical kinetochore component was identifiable in any kinetoplastid genome and it was therefore not clear whether kinetoplastids build kinetochores using conventional kinetochore proteins.
We recently succeeded in the identification of 20 kinetochore proteins (KKT1-20) in Trypanosoma brucei.
The majority are conserved among kinetoplastids but none of them has detectable homology to conventional kinetochore proteins, suggesting that kinetoplastids build kinetochores using a distinct set of proteins. By characterizing these unconventional kinetochore proteins in vivo and in vitro, my group aims to reveal the mechanism of chromosome segregation in T. brucei. Obtained insights should lead to a better understanding of the eukaryotic chromosome segregation machinery and may also provide hints about the origin and evolution of the segregation apparatus.
Etiologically, T. brucei causes African sleeping sickness, which is invariably lethal if untreated and is responsible for more than 10,000 deaths annually in sub-Saharan Africa. The current therapy is highly toxic and there is little prospect of vaccine development due to antigenic variation. Therefore, understanding the biology of trypanosomes is also medically important to facilitate drug design that specifically kills parasites. Furthermore, obtained insights in T. brucei should also lead to a better understanding of other related trypanosomatids that also cause devastating human diseases (e.g. Chagas disease caused by Trypanosoma cruzi and leishmaniasis caused by Leishmania species).
- Drinnenberg IA and Akiyoshi B (in press). Evolutionary lessons from species with unique kinetochores. In: Black BE (ed) Centromeres and Kinetochores, Springer series ‘Progress in Molecular and Subcellular Biology’
- Akiyoshi B (2016) The unconventional kinetoplastid kinetochore: from discovery toward functional understanding. Biochemical Society Transactions 44(5): 1201-1217
- Nerusheva OO and Akiyoshi B (2016) Divergent polo box domains underpin the unique kinetoplastid kinetochore. Open Biology 6: 150206
- Akiyoshi B and Gull K (2014) Discovery of unconventional kinetochores in kinetoplastids. Cell 156(6): 1247-58
- Akiyoshi B and Gull K (2013) Evolutionary cell biology of chromosome segregation: insights from trypanosomes. Open Biology 3: 130023
(A) Mitotic chromosome segregation.
(B) Cell division cycle of Trypanosoma brucei. Trypanosomes possess two DNA-containing organelles, kinetoplast (a structure in the mitochondrion that contains mitochondrial DNA) and nucleus, both of which must be segregated faithfully.
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