Inheritance of the reduced mitochondria of Giardia intestinalis is coupled to the flagellar maturation cycle

Abstract

Background The presence of mitochondria is a distinguishing feature between prokaryotic and eukaryotic cells. It is currently accepted that the evolutionary origin of mitochondria coincided with the formation of eukaryotes and from that point control of mitochondrial inheritance was required. Yet, the way the mitochondrial presence has been maintained throughout the eukaryotic cell cycle remains a matter of study. Eukaryotes control mitochondrial inheritance mainly due to the presence of the genetic component; still only little is known about the segregation of mitochondria to daughter cells during cell division. Additionally, anaerobic eukaryotic microbes evolved a variety of genomeless mitochondria-related organelles (MROs), which could be theoretically assembled de novo, providing a distinct mechanistic basis for maintenance of stable mitochondrial numbers. Here, we approach this problem by studying the structure and inheritance of the protist Giardia intestinalis MROs known as mitosomes. Results We combined 2D stimulated emission depletion (STED) microscopy and focused ion beam scanning electron microscopy (FIB/SEM) to show that mitosomes exhibit internal segmentation and conserved asymmetric structure. From a total of about forty mitosomes, a small, privileged population is harnessed to the flagellar apparatus, and their life cycle is coordinated with the maturation cycle of G. intestinalis flagella. The orchestration of mitosomal inheritance with the flagellar maturation cycle is mediated by a microtubular connecting fiber, which physically links the privileged mitosomes to both axonemes of the oldest flagella pair and guarantees faithful segregation of the mitosomes into the daughter cells. Conclusion Inheritance of privileged Giardia mitosomes is coupled to the flagellar maturation cycle. We propose that the flagellar system controls segregation of mitochondrial organelles also in other members of this supergroup (Metamonada) of eukaryotes and perhaps reflects the original strategy of early eukaryotic cells to maintain this key organelle before mitochondrial fusion-fission dynamics cycle as observed in Metazoa was established.

Efficient CRISPR/Cas9-mediated gene disruption in the tetraploid protist Giardia intestinalis

“…For immunofluorescence, the cells were labelled as described [ 56 ]. Briefly, the cells were fixed by 1% paraformaldehyde for 30 min at 37°C.…”

A core UPS molecular complement implicates unique endocytic compartments at the parasite-host interface in Giardia lamblia

“…Identification of a UPS-associated protein complex at the PV/PECs surface Giardia is known for its unique subcellular composition with only few endomembrane compartments (Acosta-Virgen et al, 2018;Soltys et al, 1996;Tůmová et al, 2021). PV/PECs are positioned at the parasite-host interface as the sole gateway into the Giardia cell (Abodeely et al, 2009;Cernikova et al, 2018;Rivero et al, 2013;Zumthor et al, 2016;Santos et al, 2022) and with some speculation on their involvement in secretion or excretion (Benchimol & de Souza, 2022;Midlej et al, 2019;Moyano et al, 2019).…”

The Giardia ventrolateral flange is a lamellar membrane protrusion that supports attachment

“…All other steps, i.e. postfixation, ultrathin embedding, mounting, imaging in a Zeiss Auriga FIB/SEM workstation operating under SmartSEM (Carl Zeiss Microscopy, Oberkochen, Germany) and image analysis using Amira (Thermo Fisher Scientific, USA) were carried out as described in [ 70 , 71 ].…”