Transcriptomic responses of Biomphalaria pfeifferi to Schistosoma mansoni: Investigation of a neglected African snail that supports more S. mansoni transmission than any other snail species

Abstract

BackgroundBiomphalaria pfeifferi is highly compatible with the widespread human-infecting blood fluke Schistosoma mansoni and transmits more cases of this parasite to people than any other snail species. For these reasons, B. pfeifferi is the world’s most important vector snail for S. mansoni, yet we know relatively little at the molecular level regarding the interactions between B. pfeifferi and S. mansoni from early-stage sporocyst transformation to the development of cercariae.Methodology/Principal findingsWe sought to capture a portrait of the response of B. pfeifferi to S. mansoni as it occurs in nature by undertaking Illumina dual RNA-Seq on uninfected control B. pfeifferi and three intramolluscan developmental stages (1- and 3-days post infection and patent, cercariae-producing infections) using field-derived west Kenyan specimens. A high-quality, well-annotated de novo B. pfeifferi transcriptome was assembled from over a half billion non-S. mansoni paired-end reads. Reads associated with potential symbionts were noted. Some infected snails yielded fewer normalized S. mansoni reads and showed different patterns of transcriptional response than others, an indication that the ability of field-derived snails to support and respond to infection is variable. Alterations in transcripts associated with reproduction were noted, including for the oviposition-related hormone ovipostatin and enzymes involved in metabolism of bioactive amines like dopamine or serotonin. Shedding snails exhibited responses consistent with the need for tissue repair. Both generalized stress and immune factors immune factors (VIgLs, PGRPs, BGBPs, complement C1q-like, chitinases) exhibited complex transcriptional responses in this compatible host-parasite system.SignificanceThis study provides for the first time a large sequence data set to help in interpreting the important vector role of the neglected snail B. pfeifferi in transmission of S. mansoni, including with an emphasis on more natural, field-derived specimens. We have identified B. pfeifferi targets particularly responsive during infection that enable further dissection of the functional role of these candidate molecules.

Transcriptional responses ofBiomphalaria pfeifferiandSchistosoma mansonifollowing exposure to niclosamide, with evidence for a synergistic effect on snails following exposure to both stressors

“…One such transcript was homologous to CD109 antigen-like, a thioestercontaining protein, which is highly enriched in plasma from both resistant and susceptible strains of B. glabrata containing miracidia transforming into mother sporocysts [58]. We also noted up-regulation of a transcript identified as complement C1q-like protein that we have reported to be up-regulated in early S. mansoni-infected B. pfeifferi [23]. Fibrinogen-related proteins (FREPs) 1 and 2 were both up-regulated after niclosamide exposure; FREP2 was also up-regulated in S. mansoni-shedding B. pfeifferi [23].…”

“…Overall B. pfeifferi and S. mansoni transcriptomic responses to molluscicide exposure Relative to uninfected and untreated control B. pfeifferi, the overall differential gene expression responses were measured for snails i) with shedding S. mansoni infections only, ii) exposed for 24 h to a sublethal dose of niclosamide only, or iii) harboring shedding S. mansoni infections and exposed to niclosamide ( Fig 1A). The responses of shedding snails relative to unexposed controls have been discussed extensively by Buddenborg et al (2017). With respect to molluscicide exposure, this is the first Illumina-based view of the transcriptomics response for any species of planorbid snail, and supplements and extends the view provided by the microarray study for uninfected B. glabrata of Zhang et al [16].…”

“…Snails shedding only S. mansoni cercariae and non-shedding controls were used in this study. More details of collections and processing can be found in Buddenborg et al [23][24].…”

“…RNA extraction, library preparation, sequencing procedures, and sequencing summaries can be found in Buddenborg et al [23,24]. Illumina RNA sequencing reads underwent extensive processing in order to separate host, parasite, and potential symbiont reads.…”

“…In addition, we examined the transcriptional responses to the same dose of molluscicide of B. pfeifferi harboring cercariae-producing S. mansoni infections. We were able to compare the responses of the above snails to both uninfected and infected B. pfeifferi not exposed to molluscicides (see companion studies [23,24]). For both the previous and present studies, we chose to examine the responses of snails recently removed from field habitats and therefore considered to be more representative of what might be expected of snails comprising natural populations actually exposed to molluscicides.…”