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

<div><p>Background</p><p><i>Biomphalaria pfeifferi</i> is highly compatible with the widespread human-infecting blood fluke <i>Schistosoma mansoni</i> and transmits more cases of this parasite to people than any other snail species. For these reasons, <i>B</i>. <i>pfeifferi</i> is the world’s most important vector snail for <i>S</i>. <i>mansoni</i>, yet we know relatively little at the molecular level regarding the interactions between <i>B</i>. <i>pfeifferi and S</i>. <i>mansoni</i> from early-stage sporocyst transformation to the development of cercariae.</p><p>Methodology/Principal findings</p><p>We sought to capture a portrait of the response of <i>B</i>. <i>pfeifferi</i> to <i>S</i>. <i>mansoni</i> as it occurs in nature by undertaking Illumina dual RNA-Seq on uninfected control <i>B</i>. <i>pfeifferi</i> 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 <i>de novo B</i>. <i>pfeifferi</i> transcriptome was assembled from over a half billion non-<i>S</i>. <i>mansoni</i> paired-end reads. Reads associated with potential symbionts were noted. Some infected snails yielded fewer normalized <i>S</i>. <i>mansoni</i> 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.</p><p>Significance</p><p>This study provides for the first time a large sequence data set to help in interpreting the important vector role of the neglected snail <i>B</i>. <i>pfeifferi</i> in transmission of <i>S</i>. <i>mansoni</i>, including with an emphasis on more natural, field-derived specimens. We have identified <i>B</i>. <i>pfeifferi</i> targets particularly responsive during infection that enable further dissection of the functional role of these candidate molecules.</p></div

Illumina sequencing and <i>B</i>. <i>pfeifferi de novo</i> transcriptome assembly summary metrics.

<p>Illumina sequencing and <i>B</i>. <i>pfeifferi de novo</i> transcriptome assembly summary metrics.</p

Highly up- or down-regulated <i>B</i>. <i>pfeifferi</i> CDS whose response may be required for maintaining a patent <i>S</i>. <i>mansoni</i> infection.

<p>Highly up- or down-regulated <i>B</i>. <i>pfeifferi</i> CDS whose response may be required for maintaining a patent <i>S</i>. <i>mansoni</i> infection.</p

Samples used for the study with total read numbers and the percent of reads mapping to the <i>S</i>. <i>mansoni</i> genome that were filtered prior to <i>de novo</i> assemblies.

<p>Samples used for the study with total read numbers and the percent of reads mapping to the <i>S</i>. <i>mansoni</i> genome that were filtered prior to <i>de novo</i> assemblies.</p

Differential expression of <i>Biomphalaria pfeifferi</i> defense-related CDS in 1d, 3d, and shedding snails.

<p>(A) Defense CDS in the 3v3 DE analysis. (B) Pie charts of proportions of CDS found to be DE in 3v3, 3v2, and 3v1 analyses. (C) Heat maps show expression levels from each of the three DE analyses highlighting the most relevant biological functional groups. Note that the 3v3 comparison includes all 3 infected snails within a time point, whereas 3v2 includes the two infected snails with the most <i>S</i>. <i>mansoni</i> reads and the 3v1 includes only the infected snail with the fewest <i>S</i>. <i>mansoni</i> reads.</p

Highlights of general, reproductive, and immune responses of <i>B</i>. <i>pfeifferi</i> in response to <i>S</i>. <i>mansoni</i> infection.

<p>Highlights of general, reproductive, and immune responses of <i>B</i>. <i>pfeifferi</i> in response to <i>S</i>. <i>mansoni</i> infection.</p

Number of polypeptides queried in various molluscs and matches with <i>B</i>. <i>pfeifferi</i> TransDecoder-predicted ORFs.

<p>Number of polypeptides queried in various molluscs and matches with <i>B</i>. <i>pfeifferi</i> TransDecoder-predicted ORFs.</p

<i>Biomphalaria pfeifferi</i> CDS identified as neuropeptides, hormones, or involved in reproduction that are differentially expressed in 1d, 3d, and shedding snails.

<p>Note that the 3v3 comparison includes all 3 infected snails within a time point, whereas 3v2 includes the two infected snails with the most <i>S</i>. <i>mansoni</i> reads and the 3v1 includes only the infected snail with the fewest <i>S</i>. <i>mansoni</i> reads.</p

Overview of novel bioinformatics pipeline developed to isolate and analyze <i>B</i>. <i>pfeifferi</i> transcriptomic expression from dual RNA-Seq data.

<p>Overview of novel bioinformatics pipeline developed to isolate and analyze <i>B</i>. <i>pfeifferi</i> transcriptomic expression from dual RNA-Seq data.</p

Sum of non-<i>B</i>. <i>pfeifferi de novo</i> assembled CDS for each replicate. CDS were counted as present if read count >0.

<p>Sum of non-<i>B</i>. <i>pfeifferi de novo</i> assembled CDS for each replicate. CDS were counted as present if read count >0.</p