Positional Dynamics and Glycosomal Recruitment of Developmental Regulators during Trypanosome Differentiation.

Balázs Szöőr,Keith R Matthews,Markus Engstler,Dorina V Simon,Timothy Krüger,Federico Rojas,Derrick R Robinson,Julie Young,Christian Tschudi

doi:10.1128/mbio.00875-19

Abstract

Glycosomes are peroxisome-related organelles that compartmentalize the glycolytic enzymes in kinetoplastid parasites. These organelles are developmentally regulated in their number and composition, allowing metabolic adaptation to the parasite's needs in the blood of mammalian hosts or within their arthropod vector. A protein phosphatase cascade regulates differentiation between parasite developmental forms, comprising a tyrosine phosphatase, Trypanosoma brucei PTP1 (TbPTP1), which dephosphorylates and inhibits a serine threonine phosphatase, TbPIP39, which promotes differentiation. When TbPTP1 is inactivated, TbPIP39 is activated and during differentiation becomes located in glycosomes. Here we have tracked TbPIP39 recruitment to glycosomes during differentiation from bloodstream "stumpy" forms to procyclic forms. Detailed microscopy and live-cell imaging during the synchronous transition between life cycle stages revealed that in stumpy forms, TbPIP39 is located at a periflagellar pocket site closely associated with TbVAP, which defines the flagellar pocket endoplasmic reticulum. TbPTP1 is also located at the same site in stumpy forms, as is REG9.1, a regulator of stumpy-enriched mRNAs. This site provides a molecular node for the interaction between TbPTP1 and TbPIP39. Within 30 min of the initiation of differentiation, TbPIP39 relocates to glycosomes, whereas TbPTP1 disperses to the cytosol. Overall, the study identifies a "stumpy regulatory nexus" (STuRN) that coordinates the molecular components of life cycle signaling and glycosomal development during transmission of Trypanosoma bruceiIMPORTANCE African trypanosomes are parasites of sub-Saharan Africa responsible for both human and animal disease. The parasites are transmitted by tsetse flies, and completion of their life cycle involves progression through several development steps. The initiation of differentiation between blood and tsetse fly forms is signaled by a phosphatase cascade, ultimately trafficked into peroxisome-related organelles called glycosomes that are unique to this group of organisms. Glycosomes undergo substantial remodeling of their composition and function during the differentiation step, but how this is regulated is not understood. Here we identify a cytological site where the signaling molecules controlling differentiation converge before the dispersal of one of them into glycosomes. In combination, the study provides the first insight into the spatial coordination of signaling pathway components in trypanosomes as they undergo cell-type differentiation.

Highlights

Glycosomes are peroxisome-related organelles that compartmentalize the glycolytic enzymes in kinetoplastid parasites
Our results reveal the coincidence of T. brucei PIP39 (TbPIP39) and Trypanosoma brucei PTP1 (TbPTP1) in bloodstream stumpy forms at a novel periflagellar pocket location, closely associated with a flagellar pocket endoplasmic reticulum (ER) contact site defined by T. brucei VAP (TbVAP) [22]
Slender, stumpy, and procyclic-form parasites were costained for TbPIP39 and glycosomal triosephosphate isomerase (gTIM) or for aldolase and gTIM and analyzed by confocal microscopy, with colocalization determined by global Pearson correlation using Volocity software (Fig. 1B)

Summary

Introduction

Glycosomes are peroxisome-related organelles that compartmentalize the glycolytic enzymes in kinetoplastid parasites These organelles are developmentally regulated in their number and composition, allowing metabolic adaptation to the parasite’s needs in the blood of mammalian hosts or within their arthropod vector. The dynamic regulation of organelle biogenesis or composition often involves intimate contact between the endoplasmic reticulum (ER) and the membrane of the target organelle [1] This enables the maturation and modification of organellar protein content, influencing mitochondrial, Golgi, or peroxisomal components, whereas interorganellar contacts can contribute to signaling events within cells, bringing regulatory molecules into proximity or trafficking them for degradation [2]. The same transition can be enacted in vitro by exposing stumpy forms to reduced temperature and cis-aconitate/citrate, which generates a highly synchronized differentiation model allowing cytological events to be readily tracked and quantitated in the population [15]

Methods

Results

Conclusion