The cell division cycle ofTrypanosoma brucei brucei: timing of event markers and cytoskeletal modulations

Abstract

We have analysed the timing and order of events occurring within the cell division cycle of Trypanosoma brucei . Cells in the earliest stages of the cell cycle possess a single copy of three major organelles: the nucleus, the kinetoplast and the flagellum. The first indication of progress through the cell cycle is the elongation of the pro-basal body lying adjacent to the mature basal body subtending the flagellum. This newly elongated basal body occupies a posterior position within the cell when it initiates growth of the new daughter flagellum. Genesis of two new pro-basal bodies occurs only after growth of the new daughter flagellum has been initiated. Extension of the new flagellum, together with the paraflagellar rod, then continues throughout a major portion of the cell cycle. During this period of flagellum elongation, kinetoplast division occurs and the two kinetoplasts, together with the two flagellar basal bodies, then move apart within the cell. Mitosis is then initiated and a complex pattern of organelle positions is achieved whereby a division plane runs longitudinally through the cell such that each daughter ultimately receives a single nucleus, kinetoplast and flagellum. These events have been described from observations of whole cytoskeletons by transmission electron microscopy together with detection of particular organelles by fluorescence microscopy. The order and timing of events within the cell cycle has been derived from analyses of the proportion of a given cell type occurring within an exponentially growing culture.

Mitochondrial Development during Life Cycle Differentiation of African Trypanosomes: Evidence for a Kinetoplast-dependent Differentiation Control Point

“…In the trypanosome cell cycle, the replication and segregation of kDNA is strictly regulated and coordinated with nuclear DNA replication (Sherwin and Gull, 1989). Although previous experiments have demonstrated that inhibiting nuclear DNA replication with aphidicolin does not effect the differentiation process (Matthews and Gull, 1994), differentiation in the absence of kDNA replication has not been examined previously.…”

Identification of the meiotic life cycle stage of Trypanosoma brucei in the tsetse fly

“…The PFR in the new flagellum was noticeably shorter in cells expressing YFP::MND1 than in cells expressing YFP::HOP1 (Movies S2 and S3). Given that PFR length is a measure of cell cycle progression (12), this observation suggests a way to ascertain the temporal order of expression of the YFP::HMGs. We could not measure the length of the new PFR directly in fixed cells, because that PFR runs alongside the old PFR.…”

“…1A), indicating that they were in late stages of the cell cycle. In other developmental stages, the two daughter kinetoplasts separate in G2 before mitosis (12,13).…”

“…We could not measure the length of the new PFR directly in fixed cells, because that PFR runs alongside the old PFR. Instead, we measured the distance between the starts of the old and new PFRs and used it as a proxy for the separation of the old and new basal bodies during cell division (11)(12)(13) [Fig. 3A, (a)].…”

“…Second, trypanosomes have a fixed, cage-like, microtubule cytoskeleton underlying the plasma membrane that defines the elongated cell shape and have a single flagellum subtended by a basal body that is physically linked by sets of filaments to the mitochondrion and mitochondrial genome, the kinetoplast (9)(10)(11). Inheritance of the basal body and flagellum cannot use established replication mechanisms during the reduction division of meiosis, because the generation of new organelles is linked to DNA replication (11)(12)(13), and the fixed microtubule cytoskeleton would not allow nuclear fusion without partial disassembly. Third, the process of genetic exchange in T. brucei involves mixing of mitochondrial (kinetoplast) and nuclear genomes, because hybrid progeny have hybrid kinetoplast DNA (kDNA) networks with mini-circles derived from both parents (14,15).…”