Formation and three-dimensional architecture of Leishmania adhesion in the sand fly vector

Abstract

Attachment to a substrate to maintain position in a specific ecological niche is a common strategy across biology, especially for eukaryotic parasites. During development in the sand fly vector, the eukaryotic parasite Leishmania adheres to the stomodeal valve, as the specialised haptomonad form. Dissection of haptomonad adhesion is a critical step for understanding the complete life cycle of Leishmania. Nevertheless, haptomonad studies are limited, as this is a technically challenging life cycle form to investigate. Here, we have combined three-dimensional electron microscopy approaches, including serial block face scanning electron microscopy (SBFSEM) and serial tomography to dissect the organisation and architecture of haptomonads in the sand fly. We showed that the attachment plaque contains distinct structural elements. Using time-lapse light microscopy of in vitro haptomonad-like cells, we identified five stages of haptomonad-like cell differentiation, and showed that calcium is necessary for Leishmania adhesion to the surface in vitro. This study provides the structural and regulatory foundations of Leishmania adhesion,which are critical for a holistic understanding of the Leishmania life cycle.

Genetic modification of the bee parasiteCrithidia bombifor improved visualization and protein localization

“…b) C. bombi strains 08.076 [22] and 16.075 [33] (3) Expression of fluorescent proteins with distinct subcellular localizations Crithidia bombi, like other trypanosomatids, are complex eukaryotic cells with a variety of compartments and a distinctly polarized subcellular organization [34,35]. In related species, subcellular organization can change as the parasite undergoes morphological and metabolic adaptation to different environments [35][36][37][38]. In addition to changes in cell and organelle shape, the localization of individual proteins can also vary during the cell and life cycle [35,39].…”

3D electron microscopy of theLeishmania mexicanacell cycle: Patterns of organelle duplication and segregation and their implications for parasite biology

“…We chose to examine parasites from a late stage infection at the stomodeal valve, as this gives a good number of parasites which are likely furthest removed from in vitro log phase promastigotes, giving the most extreme of comparisons. We analysed a 10-day post infection L. mexicana infected sand fly midgut SBF-SEM dataset containing 218 slices, which covered part of the stomodeal valve (Yanase et al 2023, EMPIAR-11463) (Figure 6A). Every cell examined (n=89) was in Stage 1 based on our in vitro classification, as they only had one flagellum, suggesting that these cells were in stationary phase.…”

A sticky situation: When trypanosomatids attach to insect tissues

“…Haptomonads are often rounder than swimming forms, suggesting attachment involves additional cytoskeletal rearrangements. Leishmania parasites can also attach to artificial surfaces [45,56] and detailed stages of attachment in vitro have been defined [56]. Initial attachment can occur either at the base of the flagellum or laterally at a position along the flagellum's length (Fig 2).…”

“…In a series of papers, Brooker described "hemidesmosomes" connecting the flagellum of C. fasciculata to the mosquito hindgut/artificial surfaces, as well as "desmosomes" linking the flagellum to the parasite cell body [32,59]. Several investigators have noted that these 2 structures appear connected [50,56,137]. The desmosome-like structure was subsequently renamed the flagellar attachment zone, or FAZ, and consists of a series of junctional complexes connecting the flagellum along the length of the cell body, producing the attached flagellum characteristic of juxtaform species [12,[138][139][140].…”

“…A recent study describes the structure of attached Leishmania haptomonads in detail [56]. The authors used serial block face scanning electron microscopy to create 3D representations of L. mexicana haptomonads attached to the stomodeal valve.…”