Research Article: Methyl-CpG-binding (SmMBD2/3) and chromobox (SmCBX) proteins are required for neoblast proliferation and oviposition in the parasitic blood fluke Schistosoma mansoni

Date Published: June 28, 2018

Publisher: Public Library of Science

Author(s): Kathrin K. Geyer, Sabrina E. Munshi, Helen L. Whiteland, Narcis Fernandez-Fuentes, Dylan W. Phillips, Karl F. Hoffmann, Michael H. Hsieh.


While schistosomiasis remains a significant health problem in low to middle income countries, it also represents a recently recognised threat to more economically-developed regions. Until a vaccine is developed, this neglected infectious disease is primarily controlled by praziquantel, a drug with a currently unknown mechanism of action. By further elucidating how Schistosoma molecular components cooperate to regulate parasite developmental processes, next generation targets will be identified. Here, we continue our studies on schistosome epigenetic participants and characterise the function of a DNA methylation reader, the Schistosoma mansoni methyl-CpG-binding domain protein (SmMBD2/3). Firstly, we demonstrate that SmMBD2/3 contains amino acid features essential for 5-methyl cytosine (5mC) binding and illustrate that adult schistosome nuclear extracts (females > males) contain this activity. We subsequently show that SmMBD2/3 translocates into nuclear compartments of transfected murine NIH-3T3 fibroblasts and recombinant SmMBD2/3 exhibits 5mC binding activity. Secondly, using a yeast-two hybrid (Y2H) screen, we show that SmMBD2/3 interacts with the chromo shadow domain (CSD) of an epigenetic adaptor, S. mansoni chromobox protein (SmCBX). Moreover, fluorescent in situ hybridisation (FISH) mediated co-localisation of Smmbd2/3 and Smcbx to mesenchymal cells as well as somatic- and reproductive- stem cells confirms the Y2H results and demonstrates that these interacting partners are ubiquitously expressed and found within both differentiated as well as proliferating cells. Finally, using RNA interference, we reveal that depletion of Smmbd2/3 or Smcbx in adult females leads to significant reductions (46–58%) in the number of proliferating somatic stem cells (PSCs or neoblasts) as well as in the quantity of in vitro laid eggs. Collectively, these results further expand upon the schistosome components involved in epigenetic processes and suggest that pharmacological inhibition of SmMBD2/3 and/or SmCBX biology could prove useful in the development of future schistosomiasis control strategies.

Partial Text

Characterised by a complex lifecycle alternating between two different hosts (snail and mammal) and a fresh water ecosystem, schistosomes are highly evolved human pathogens responsible for the neglected infectious disease schistosomiasis. Predominantly found in sub-tropical and tropical regions of resource-poor communities, schistosomiasis kills thousands of individuals per year and causes chronic disability in millions more [1]. Until a immunoprophylactic vaccine can be developed, existing treatment relies on chemotherapeutic administration of praziquantel (PZQ) to individuals living in endemic communities [2]. Use of a single anti-parasitic drug with a currently unknown mechanism of action (perhaps acting as a G-protein coupled receptor agonist [3]) and limited efficacy against juvenile schistosomes [4], however, raises serious concerns in meeting the ambitious targets set by the World Health Organisation for achieving schistosomiasis elimination in selected regions and countries by 2020 [5]. Therefore, furthering our understanding into how schistosomes respond to diverse environmental stimuli (water, snail or human) may simultaneously reveal the molecular processes essential for lifecycle transmission as well as the specific components suitable for next-generation anti-schistosomal drug or vaccine development. Epigenetic processes that shape chromatin modifications as well as regulate both heritable and environmentally influenced phenotypes present a rich molecular area in which to identify these key schistosome components [6].

Schistosome development is influenced by interactions with three distinct niches (freshwater ecosystem, snail intermediate host and mammal definitive host) and is molecularly controlled by genetic as well as epigenetic processes [6, 36]. While schistosomes do not harbour the extreme developmental plasticity potential exhibited by nematodes [56], their ability to remain responsive to diverse environmental signals assists in the establishment of heritable variations critical for infection success [57]. Therefore, elucidating how schistosome epigenetic components cooperatively regulate key parasitological processes and shape heritable traits will likely uncover new targets for schistosomiasis control. Here, we provide evidence for the role of SmMBD2/3 and SmCBX in the biology of schistosome somatic stem cells (neoblasts) and additionally suggest that pharmacological disruption of these interacting partners will lead to defects in the most important aspect of schistosome mediated pathology and lifecycle maintenance, egg production.