Apicoplast fission paper

Markus Meissner

14-Sep-2011

Apicoplast fission paperalveolata

Here's a taste of Markus's recent research, as described in the summary of one of his scientific papers. We've provided pop-up definitions for this since we're going to use it for a class activity.

 

Background: Apicomplexan parasites cause numerous important human diseases, including malaria and toxoplasmosis. Apicomplexa belong to the Alveolata, a group that also includes ciliates and dinoflagellates.

Apicomplexa retain a plastid organelle (the apicoplast) that was derived from an endosymbiotic relationship between the alveolate ancestor and a red alga.

The Apicoplast: An Organelle with a Green PastApicoplasts are essential for parasite growth and must correctly divide and segregate into daughter cells upon cytokinesis. Apicoplast division depends on association with the mitotic spindle, although little is known about the molecular machinery involved in this process.

Apicoplasts lack the conserved machinery that divides chloroplasts in plants and red algae, suggesting that these mechanisms are unique.

Results:

Here, we demonstrate that a dynamin-related protein in Toxoplasma gondii (TgDrpA ) localizes to punctate regions on the apicoplast surface.

We generate a conditional dominant-negative TgDrpA cell line to disrupt TgDrpA functions and demonstrate that TgDrpA is essential for parasite growth and apicoplast biogenesis.

Fluorescence recovery after photobleaching and time-lapse imaging studies provide evidence for a direct role for TgDrpA in apicoplast fission.

Conclusions:

Our data suggest that DrpA was likely recruited from the alveolate ancestor to function in fission of the symbiont and ultimately replaced the conserved division machinery of that symbiont.

 

And below is the introduction to the same paper.

We're not going to look at this in detail, so no pop-ups, but it does contain more information than the summary - which is helpful in trying to grasp what the paper is all about.

Introduction

Plastid organelles trace their evolutionary origins to cyanobacteria that were incorporated into eukaryotic cells by a process of endosymbiosis. This evolutionary history dictates that they cannot be formed de novo. Instead, existing plastids divide to give rise to daughter organelles that partition into daughter cells upon cell division. Previously studied plastids contain an FtsZ-based division apparatus retained from the cyanobacterial endosymbiont [1]. In addition, plant and red algal plastid division involves a dynamin-like protein called ARC5 (also known as DRP5B [2] and [3] ).

Apicoplasts, the nonphotosynthetic plastids of apicomplexan parasites, must correctly divide and segregate into daughter cells for parasites to remain viable [4]. Surprisingly, apicomplexan genomes lack homologs to both ARC5 and FtsZ [5], suggesting that apicoplast division is mechanistically different than that in previously studied plastids. One striking difference is the association of the apicoplast with the centrosomes of the mitotic spindle [6] and [7] . This association is thought to ensure proper segregation during cytokinesis, parceling out apicoplasts to a highly variable number of daughter cells formed in the complex apicomplexan budding process [8]. Though centrosome association provides a unifying model for segregation, it remains unclear how apicoplast fission occurs. One model suggests that fission depends on force generated by daughter cell budding [6], whereas electron microscopic studies identify apparent plastid division rings [9] and [10] , suggesting that protein components may mediate fission.

Dynamins are large GTPase proteins that function in a range of contractile processes, including the scission of endocytic vesicles, cytokinesis, nuclear remodelling, and the fission of mitochondria, chloroplasts, and peroxisome organelles [11] , [12] and [13] , and we were interested in whether dynamins had a role in apicoplast division. Apicomplexan genomes encode three dynamin-related proteins that are phylogenetically distinct from ARC5. In this study, we characterize dynamin-related protein A (DrpA) in the apicomplexan T. gondii. We demonstrate that TgDrpA is required for apicoplast fission, and we present a detailed model for how TgDrpA functions in this process.

Further reading

Fluorescence recovery after photobleaching

Words used in pop-ups

Alveolata algae breed cell chlorophyll chromosomes cytoplasm DNA
dynamins electromagnetic radiation environment evolution expression fertile flagella
flagellate fluorophore fluorescent gene genome host ingest
inherit interaction membrane molecule mutation nucleus organelle
organism phenotype photosynthesis protein protist protoplasm protozoan
radiation sequence species structure symbiosis technique template
transport ultraviolet vesicle wavelength

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