Mitochondrial genome maintenance—the kinetoplast story

Abstract

Mitochondrial DNA replication is an essential process in most eukaryotes. Similar to the diversity in mitochondrial genome size and organization in the different eukaryotic supergroups, there is considerable diversity in the replication process of the mitochondrial DNA. In this review, we summarize the current knowledge of mitochondrial DNA replication and the associated factors in trypanosomes with a focus on Trypanosoma brucei, and provide a new model of minicircle replication for this protozoan parasite. The model assumes the mitochondrial DNA (kinetoplast DNA, kDNA) of T. brucei to be loosely diploid in nature and the replication of the genome to occur at two replication centers at the opposing ends of the kDNA disc (also known as antipodal sites, APS). The new model is consistent with the localization of most replication factors and in contrast to the current model, it does not require the assumption of an unknown sorting and transport complex moving freshly replicated DNA to the antipodal sites. In combination with the previously proposed sexual stages of the parasite in the insect vector, the new model provides a mechanism for maintenance of the mitochondrial genetic diversity.

Characterization of novel and essential kinetoplast-associated proteins inTrypanosoma brucei

“…Their previous tagging resulted in associations with the kinetoplast only when an epitope was present at the N-terminus, thus leaving the C-terminus exposed (Pyrih et al, 2023), which we replicated here. These traits are shared with another characteristic kinetoplast protein, DNA topoisomerase II (Tb927.9.5590), serving as a prototypical cell-cycle dependent marker of the antipodal sites (Amodeo et al, 2022), and additionally being involved in minicircle maintenance like the former two proteins (Z. Wang & Englund, 2001).…”

“…The faithful replication of each circle into the daughter kDNA discs occurs via the decatenation of minicircles from the network by the action of disc topoisomerases and their replication in the k ineto-flagellar z one (KFZ), (Jensen & Englund, 2012; Shlomai, 2004), while a recently proposed model posits a separate replication of minicircle subsets at the two a nti p odal s ites (APS), which are large conglomerates of kDNA-associated proteins (Amodeo, Bregy, & Ochsenreiter, 2022). Mechanisms governing maxicircles replication are less clear, but DNA rings have been observed remaining in the center of the kDNA disc (Carpenter & Englund, 1995), forming a transient thread during segregation called the ‘nabelschnur’ (Jensen & Englund, 2012).…”

Cryo-electron tomography sheds light on the elastic nature of theTrypanosoma bruceitripartite attachment complex

“…Replication of this highly organized DNA network requires the organism to release the individual DNA molecules from catenation to neighboring DNA circles (Jensen & Englund, 2012). The minicircles thus are released from the network prior to replication and move to two opposing poles of the kDNA disc (known as the antipodal sites) where they are then replicated and reattached to the network (Amodeo et al, 2022; Jensen & Englund, 2012). Maxicircles on the other hand, are believed to remain attached to the network throughout the replication process.…”

“…Over the past decades, several components of the TAC have been identified (Amodeo et al, 2022; Schneider & Ochsenreiter, 2018). While most of them localize to the DMs or the ULFs, it seems that the EZF protein p197 spans the entire exclusion zone (Aeschlimann et al, 2022; Gheiratmand et al, 2013).…”

Evolutionary repurposing of trypanosomal Pam18 and Pam16 reveals a new regulatory circuit for mitochondrial genome replication

“…Maxicircles replicate like minicircles, but always remain interlocked with the kDNA. However, the details of the process and the factors required for it are not well understood 28,43 . Minicircle release and reattachment causes concentration of the catenated maxicircles in the center of the disk 35 .…”