Biology subjects

Tetzlaff, S.

Publications and source records attributed to Tetzlaff, S..

3 recordsLinked to original sources

bioRxiv2026

TgmRHel drives unified RNA processing of coxI mRNA generated from a complex mitochondrial genomic context

The mitochondrial genome of Toxoplasma gondii is highly fragmented and recombination-prone, creating a structurally dynamic genetic landscape. How such a genome is used efficiently to produce functional mRNAs remains unclear: it is unknown whether transcription draws from many alternative genomic configurations or a restricted subset, and how any resulting precursor RNAs are processed into mature transcripts. More broadly, mitochondrial RNA processing mechanisms in this system are poorly understood. Here, we show that recombination of the T. gondii mitochondrial genome generates a diverse population of structurally distinct precursor RNAs for the essential cytochrome c oxidase subunit I (coxI) protein. Rather than being derived from a single defined primary transcript, these heterogeneous precursors are unified into a single mature mRNA through a post-transcriptional mechanism dependent on the DEAD-box RNA helicase TgmRHel. TgmRHel is required for 5'-end processing of coxI mRNA and for the accumulation of mitochondrial rRNAs, both of which are essential for Complex IV biogenesis, oxidative phosphorylation, and parasite survival. Loss of TgmRHel leads to the accumulation of diverse coxI precursor RNAs and a failure to generate the mature transcript. Our findings reveal an unexpected genome-transcriptome interface in which extensive genomic variability is not suppressed at the DNA level but instead resolved through RNA helicase-mediated processing. This work establishes a new conceptual framework for how gene expression fidelity can be maintained in the context of highly dynamic, recombining genomes.

molecular biology↗

bioRxiv2026

Helical Repeat Protein mRSiC is Required for rRNA Fragment Accumulation in T. gondii Mitochondria

Myzozoans, including apicomplexan parasites, possess highly reduced and unusual mitochondrial genomes that encode two to three respiratory chain subunits and extensively fragmented rRNAs forming a divergent mitoribosome. Heptatricopeptide repeat (HPR) proteins are expanded in myzozoans, with some functioning as mitoribosomal constitutes. Additional HPR proteins have been proposed to function in post-transcriptional processes of mitochondrial gene expression, though their specific roles remain unexplored. We present a phylogenetic analysis of HPR proteins that reveals extensive lineage-specific expansions, consistent with diversifications of mitochondrial gene expression systems within myzozoans. We further characterize mRSiC, a coccidian-specific HPR found in Toxoplasma gondii and its closest relatives. Using sRNA sequencing and RNA gel blot analyses, we show that mRSiC is required for the stabilization of two coccidian-specific mitochondrial sRNAs, RNA33 and RNA42. Loss of mRSiC causes rapid depletion of these RNAs, followed by secondary reductions of rRNA fragments, defects in the respiratory chain, and impaired parasite proliferation. Together, these findings highlight the importance of HPRs in apicomplexan mitochondrial gene expression and illustrate how lineage-specific RNA-binding factors support highly derived mitochondrial expression systems.

molecular biology↗

bioRxiv2023

Ribosomal Incorporation of Short RNAs from Mitochondrial Genome Recombination Sites in Toxoplasma gondii

The mitochondrial genomes of apicomplexans comprise merely three protein-coding genes, alongside a set of thirty to forty genes encoding small RNAs (sRNAs), many of which exhibit homologies to rRNA from E. coli. The expression status and integration of these short RNAs into ribosomes remains unclear and direct evidence for active ribosomes within apicomplexan mitochondria is still lacking. In this study, we conducted small RNA sequencing on the apicomplexan Toxoplasma gondii to investigate the occurrence and function of mitochondrial sRNAs. To enhance the analysis of sRNA sequencing outcomes, we also re-sequenced the T. gondii mitochondrial genome using an improved organelle enrichment protocol and Nanopore sequencing. It has been established previously that the T. gondii genome comprises 21 sequence blocks that undergo recombination among themselves but that their order is not entirely random. The enhanced coverage of the mitochondrial genome allowed us to characterize block combinations at increased resolution. Employing this refined genome for sRNA mapping, we find that many small RNAs originated from the junction sites between protein-coding blocks and rRNA sequence blocks. Surprisingly, such block border sRNAs were incorporated into polysomes together with canonical rRNA fragments and mRNAs. In conclusion, apicomplexan ribosomes are active within polysomes and are indeed assembled through the integration of sRNAs, including previously undetected sRNAs with merged mRNA-rRNA sequences. Our findings lead to the hypothesis that T. gondiis block-based genome organization enables the dual utilization of mitochondrial sequences as both messenger RNAs and ribosomal RNAs, potentially establishing a link between the regulation of rRNA and mRNA expression.

molecular biology↗