Combined nanometric and phylogenetic analysis of unique endocytic compartments in Giardia lamblia sheds light on the evolution of endocytosis in Fornicata

Abstract

Giardia lamblia, a parasitic protist of the metamonada supergroup, has evolved one of the most diverged endocytic compartment systems investigated so far. Peripheral endocytic compartments, currently known as peripheral vesicles or vacuoles (PVs), perform bulk uptake of fluid phase material which is then digested and sorted either to the cell cytosol or back to the extracellular space. Here, we present a quantitative morphological characterization of these organelles using volumetric electron microscopy and super-resolution microscopy (SRM). We defined a morphological classification for the heterogenous population of PVs and performed a comparative analysis of PVs and endosome-like organelles in representatives of phylogenetically-related taxa, Spironucleus spp. and Tritrichomonas foetus. To investigate the as-yet insufficiently understood connection between PVs and clathrin assemblies in G. lamblia, we further performed an in-depth search for two key elements of the endocytic machinery, clathrin heavy chain (CHC) and clathrin light chain (CLC) across different lineages in Metamonada. Our data point to the loss of a bona fide CLC in the last Fornicata common ancestor (LFCA) with the emergence of a protein analogous to CLC (GlACLC) in the Giardia genus. Taken together, this provides the first comprehensive nanometric view of the Giardia endocytic system architecture and sheds light on the evolution of GLACLC analogues in the Fornicata supergroup and, specific to Giardia, as a possible adaptation to the formation and maintenance of stable clathrin assemblies at PVs.

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

“…GL50803_27521 Histone H2A localises to nuclei while GL50803_15383 Peroxiredoxin-1 shows an ER localisation pattern. GL50803_102108 Gl CHC is included as a bona fide PV/PECs localised protein (Cernikova et al, 2020b; Santos et al, 2022; Zumthor et al, 2016a). The PV/PECs-enriched bare zone is highlighted with a white arrowhead.…”

“…Giardia is known for its unique subcellular composition with only few endomembrane compartments (Acosta-Virgen et al, 2018; Benchimol & Souza, 2022; Faso & Hehl, 2019; 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 ten most enriched hits aside from the bait protein were visualized with Cytoscape (Shannon et al 2003) reviewer_pxd035195@ebi.ac.uk, password: o8PUqwbH) and PXD035190 reviewer account details (username: reviewer_pxd035190@ebi.ac.uk, password: J1Q36yqx). GlCHC is included as a bona fide PV/PECs localised protein (Cernikova et al, 2020b;Santos et al, 2022;Zumthor et al, 2016a). The PV/PECs-enriched bare zone is highlighted with a white arrowhead.…”

“…Giardia presents a simplified endomembrane system, with only five membrane-bound compartments, including an extensive ER, and no detectable Golgi apparatus (Elias et al, 2008; Hehl & Marti, 2004; Marti & Hehl, 2003) despite constitutive trafficking of secretory variant surface proteins (Faso & Hehl, 2011, 2019; McCaffery et al, 1994). The sole port of entry for fluid-phase material in the Giardia cell are the recently renamed (Santos et al, 2022) peripheral vacuoles/peripheral endocytic compartments (PVs/PECs), small (ca. 200nm) highly polymorphic organelles (Cernikova et al, 2018, 2019, 2020; Pipaliya et al, 2021; Zumthor et al, 2016).…”

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

“…Giardia presents a simplified endomembrane system, with only five membrane-bound compartments, including an extensive ER, and no detectable Golgi apparatus [ 12–14 ] despite constitutive trafficking of secretory variant surface proteins [ 15–17 ]. The sole port of entry for fluid-phase material in the Giardia cell are the recently renamed [ 18 ] peripheral vacuoles/peripheral endocytic compartments (PVs/PECs), small (ca. 200 nm) highly polymorphic organelles [19–22,51].…”