Elsevier

Current Opinion in Microbiology

Volume 34, December 2016, Pages 82-89
Current Opinion in Microbiology

Developmental differentiation in Leishmania lifecycle progression: post-transcriptional control conducts the orchestra

https://doi.org/10.1016/j.mib.2016.08.004Get rights and content

Highlights

  • Quiescence is associated with differentiation in Leishmania spp.

  • RNA and protein reprogramming is necessary for differentiation in Leishmania spp.

  • RNA and protein levels do not always correlate during Leishmania spp. differentiation.

  • The RNA master regulons for parasite lifecycle progression remains uncharacterized.

The successful progression of Leishmania spp. through their lifecycle entails a series of differentiation processes; the proliferative procyclic promastigote forms become quiescent, human-infective metacyclic promastigotes during metacyclogenesis in the sandfly vector, which then differentiate into amastigotes during amastigogenesis in the mammalian host. The progression to these infective forms requires two components: environmental cues and a coordinated cellular response. Recent studies have shown that the Leishmania cellular transformation into mammalian-infective stages is triggered by broad changes in the absolute and relative RNA and protein levels. In this review, we will discuss the implications of Leishmania transcriptomic and proteomic fluctuations, which adapt the parasitic cell for survival.

Introduction

Leishmania spp. are protozoan parasites which belong to the order Kinetoplastida and are the aetiological agents of the human leishmaniases. These diseases cause 20 000–40 000 deaths per year and threaten 310 million people worldwide [1]. Leishmania protozoan flagellates have evolved from an ancestral monoxenous life in insects to a complex dixenous parasitic lifecycle which alternates between a sandfly vector and mammalian hosts [2, 3]. As a key driver for this evolutionary adaptation, Leishmania parasites remodel their cellular architecture and physiological properties for survival through stressful environmental conditions inside and out of the insect alimentary tract. Specific developmental adaptations have shaped the appearance of transmission-optimised metacyclic promastigote forms in the insect vector and intracellular amastigote forms in mammalian leukocytes. These two consecutive differentiation processes are called metacyclogenesis, and amastigogenesis (Figure 1).

An unusual characteristic of kinetoplastid cells is the near absence of transcriptional control. Genes are arranged and transcribed into long polycistronic transcription units (PTUs) and, in the context of the Leishmania spp. genomes, subjected to a high genomic plasticity which results in frequent aneuploidies and copy number variations [4, 5]. Once transcribed, the mRNA is matured by trans-splicing of a capped Spliced Leader sequence (SL) to the 5′ end of all mRNAs coupled to 3′ cleavage and polyadenylation in order to be targeted for nuclear export [6, 7, 8]. Reduced transcriptional regulation makes these organisms extreme models for studying post-transcriptional and post-translational processes in cell development.

In prokaryotic and eukaryotic organisms post-transcriptional and post-translational networks enable immediate response and survival during environmental stress [9, 10, 11, 12, 13, 14, 15, 16, 17, 18]. Examples of this include small molecules termed riboswitches, that bind regulatory elements in mRNA UTRs and target them for swift degradation, or subcellular storage granules containing translationally arrested RNAs that form in response to specific conditions in many cell types [18, 19, 20].

The main differentiation processes within the Leishmania parasite lifecycle can be replicated in culture to a degree. This convenience makes the Leishmania parasite a good model system to study developmental processes in infectious disease. In this review, we will discuss recent reports highlighting the dynamic nature of RNA and its translation into protein during differentiation in Leishmania spp. parasites.

Section snippets

RNA and protein changes during metacyclogenesis

Metacyclogenesis is the developmental process undertaken by leptomonad forms once they reach the anterior midgut of an infected sandfly (Figure 1). Metacyclic promastigotes are defined as mammalian infective, highly motile, non-replicative cells, characterized by a large flagellum at least twice the length of the slender cell body (∼8 μm × 1.2–1.5 μm) [21, 22]. Another defining characteristic is that the major promastigote-stage parasite surface glycoconjugate lipophosphoglycan (LPG), composed of

RNA and protein changes during amastigogenesis

Amastigogenesis is the developmental process undertaken by metacyclic promastigote forms after being regurgitated by the insect vector and phagocytosed by a number of host cell types (inflammatory monocytes, neutrophils, dendritic cells and macrophages) (Figure 1). This process will lead to the formation of non-motile (shortened flagella (∼1 μm)), ovoid-shaped cells (∼3–5 μm × 2–3 μm) which replicate intracellularly inside parasite-harboring compartments termed parasitophorous vacuoles (PVs) [41, 42

Comparing RNA and protein expression throughout Leishmania spp. lifecycle progression

In the light of experiments covered in this review, we can conclude that (i) absolute and relative RNA levels during the lifecycle of Leishmania spp. are continuously changing in response to environmental cues, implicating post-transcriptional control as a key regulatory process in parasite differentiation. In L. mexicana ∼14% of all genes are stage regulated (>2-fold change) between amastigote and procyclic forms [48]. (ii) The absolute and relative RNA and protein levels show poor correlation

Conclusions

From high-throughput studies, we have gained many insights into global remodeling of RNA and protein content during developmental differentiation in Leishmania spp., yet we still do not hold a firm grasp of how these processes are promoted and executed by the cells. In particular, we lack a full understanding of how mRNA stability, decay or translation are controlled in near absence of transcriptional regulation. Very little is defined about the dynamics and regulation of messenger

References and recommended reading

Papers of particular interest, published within the period of review, have been highlighted as:

  • •• of outstanding interest

Acknowledgements

We would like to thank Prof. Jeremy Mottram for useful comments regarding this review and apologize to colleagues whose references we have not cited due to space constraints. This work was supported by the Medical Research Council (MRC) (project reference: MR/L00092X/1).

References (62)

  • P.J. Alcolea et al.

    Influence of the microenvironment in the transcriptome of Leishmania infantum promastigotes: sand fly versus culture

    PLoS Negl Trop Dis

    (2016)
  • M. Fiebig et al.

    Comparative life cycle transcriptomics revises Leishmania mexicana genome annotation and links a chromosome duplication with parasitism of vertebrates

    PLoS Pathog

    (2015)
  • L.A.L. Dillon et al.

    Simultaneous transcriptional profiling of Leishmania major and its murine macrophage host cell reveals insights into host-pathogen interactions

    BMC Genomics

    (2015)
  • C. Chow et al.

    Promastigote to amastigote differentiation of Leishmania is markedly delayed in the absence of PERK eIF2alpha kinase-dependent eIF2alpha phosphorylation

    Cell Microbiol

    (2011)
  • J. Alvar et al.

    Leishmaniasis worldwide and global estimates of its incidence

    PLoS ONE

    (2012)
  • N. Kraeva et al.

    Leptomonas seymouri: adaptations to the dixenous life cycle analyzed by genome sequencing, transcriptome profiling and co-infection with Leishmania donovani

    PLOS Pathog

    (2015)
  • A.C. Ivens

    The genome of the kinetoplastid parasite, Leishmania major

    Science

    (2005)
  • M.B. Rogers et al.

    Genomic confirmation of hybridisation and recent inbreeding in a vector-isolated Leishmania population

    PLoS Genet

    (2014)
  • X. Liang et al.

    trans and cis splicing in trypanosomatids: mechanism, factors, and regulation

    Eukaryot Cell

    (2003)
  • M. Bühlmann et al.

    NMD3 regulates both mRNA and rRNA nuclear export in African trypanosomes via an XPOI-linked pathway

    Nucleic Acids Res

    (2015)
  • A. Dostalova et al.

    The nuclear mRNA export receptor Mex67-Mtr2 of Trypanosoma brucei contains a unique and essential zinc finger motif: nuclear mRNA export in Trypanosoma brucei

    Mol Microbiol

    (2013)
  • C. Vogel et al.

    Insights into the regulation of protein abundance from proteomic and transcriptomic analyses

    Nat Rev Genet

    (2012)
  • S. Iuchi et al.

    Cellular and molecular physiology of Escherichia coli in the adaptation to aerobic environments

    J Biochem (Tokyo)

    (1996)
  • P. Walrad et al.

    Differential Trypanosome surface coat regulation by a CCCH protein that co-associates with procyclin mRNA cis-elements

    PLoS Pathog

    (2009)
  • N.G. Kolev et al.

    Developmental progression to infectivity in Trypanosoma brucei triggered by an RNA-binding protein

    Science

    (2012)
  • P.K. Padmanabhan et al.

    Apoptosis-like programmed cell death induces antisense ribosomal RNA (rRNA) fragmentation and rRNA degradation in Leishmania

    Cell Death Differ

    (2012)
  • A. Dupé et al.

    An Alba-domain protein contributes to the stage-regulated stability of amastin transcripts in Leishmania

    Mol Microbiol

    (2014)
  • P.B. Walrad et al.

    The post-transcriptional trans-acting regulator, TbZFP3, co-ordinates transmission-stage enriched mRNAs in Trypanosoma brucei

    Nucleic Acids Res

    (2012)
  • A. Cassola

    RNA granules living a post-transcriptional life: the Trypanosomes’ case

    Curr Chem Biol

    (2011)
  • M. Fritz et al.

    Novel insights into RNP granules by employing the trypanosome's microtubule skeleton as a molecular sieve

    Nucleic Acids Res

    (2015)
  • R. da Silva et al.

    Metacyclogenesis is a major determinant of Leishmania promastigote virulence and attenuation

    Infect Immun

    (1987)
  • Cited by (41)

    • Deep learning for microscopic examination of protozoan parasites

      2022, Computational and Structural Biotechnology Journal
      Citation Excerpt :

      34,298 microscopic images of multiple parasites and host cells were obtained, including Plasmodium, Toxoplasma, Babesia, Leishmania, Trypanosome, Trichomonad, Red blood cells and Leukocytes. It is worth noting that the current publicly available Leishmania datasets are very rare, and the flagellated promastigote stage present only in the midgut of insect vectors (sandflies) [54]. The images of Leishmania collected and presented here with promastigote morphology [29] might be not useful for medical diagnostic, but this dataset is still very useful for the study the life cycle of the Leishmania parasite, and would be also useful for deep learning training and model development.

    • Leishmania (V.) braziliensis infection promotes macrophage autophagy by a LC3B-dependent and BECLIN1-independent mechanism

      2021, Acta Tropica
      Citation Excerpt :

      Amastigotes develop within the phagocytic cells (inside parasitophorous vacuoles) located in the reticular connective tissue of mammals. Upon phlebotomine sandflies’ blood meal, amastigotes disrupt mammalian macrophages and in the vector's midgut, differentiate into promastigotes, which are eliminated during regurgitation upon another vertebrate host (de Pablos et al., 2016). This interaction between host cells (especially macrophages) and Leishmania spp. regulates how infection and its persistence will contribute to lesion/healing axis and host immune response (Moradin and Descoteaux, 2012).

    View all citing articles on Scopus
    View full text