PIWI silencing mechanism involving the retrotransposon nimbus orchestrates resistance to infection with Schistosoma mansoni in the snail vector, Biomphalaria glabrata.

BACKGROUND: Schistosomiasis remains widespread in many regions despite efforts at its elimination. By examining changes in the transcriptome at the host-pathogen interface in the snail Biomphalaria glabrata and the blood fluke Schistosoma mansoni, we previously demonstrated that an early stress response in juvenile snails, manifested by induction of heat shock protein 70 (Hsp 70) and Hsp 90 and of the reverse transcriptase (RT) domain of the B. glabrata non-LTR- retrotransposon, nimbus, were critical for B. glabrata susceptibility to S. mansoni. Subsequently, juvenile B. glabrata BS-90 snails, resistant to S. mansoni at 25°C become susceptible by the F2 generation when maintained at 32°C, indicating an epigenetic response. METHODOLOGY/PRINCIPAL FINDINGS: To better understand this plasticity in susceptibility of the BS-90 snail, mRNA sequences were examined from S. mansoni exposed juvenile BS-90 snails cultured either at 25°C (non-permissive temperature) or 32°C (permissive). Comparative analysis of transcriptomes from snails cultured at the non-permissive and permissive temperatures revealed that whereas stress related transcripts dominated the transcriptome of susceptible BS-90 juvenile snails at 32°C, transcripts encoding proteins with a role in epigenetics, such as PIWI (BgPiwi), chromobox protein homolog 1 (BgCBx1), histone acetyltransferase (BgHAT), histone deacetylase (BgHDAC) and metallotransferase (BgMT) were highly expressed in those cultured at 25°C. To identify robust candidate transcripts that will underscore the anti-schistosome phenotype in B. glabrata, further validation of the differential expression of the above transcripts was performed by using the resistant BS-90 (25°C) and the BBO2 susceptible snail stock whose genome has now been sequenced and represents an invaluable resource for molecular studies in B. glabrata. A role for BgPiwi in B. glabrata susceptibility to S. mansoni, was further examined by using siRNA corresponding to the BgPiwi encoding transcript to suppress expression of BgPiwi, rendering the resistant BS-90 juvenile snail susceptible to infection at 25°C. Given transposon silencing activity of PIWI as a facet of its role as guardian of the integrity of the genome, we examined the expression of the nimbus RT encoding transcript at 120 min after infection of resistant BS90 piwi-siRNA treated snails. We observed that nimbus RT was upregulated, indicating that modulation of the transcription of the nimbus RT was associated with susceptibility to S. mansoni in BgPiwi-siRNA treated BS-90 snails. Furthermore, treatment of susceptible BBO2 snails with the RT inhibitor lamivudine, before exposure to S. mansoni, blocked S. mansoni infection concurrent with downregulation of the nimbus RT transcript and upregulation of the BgPiwi encoding transcript in the lamivudine-treated, schistosome-exposed susceptible snails. CONCLUSIONS AND SIGNIFICANCE: These findings support a role for the interplay of BgPiwi and nimbus in the epigenetic modulation of plasticity of resistance/susceptibility in the snail-schistosome relationship.

Report of Platythomisus octomaculatus (C. L. Koch, 1845) and Platythomisus sudeepi Biswas, 1977 from India (Araneae, Thomisidae).

BACKGROUND: The genus Platythomisus Doleschall, 1859 presently comprises 13 valid species, nine known from Africa and four from Asia. All Platythomisus species are known from females only, except P. jucundus Thorell, 1894 and P. sudeepi Biswas, 1977 from both sexes and P. quadrimaculatus from juvenile. Only, P. sudeepi was reported from India. NEW INFORMATION: Platythomisus octomaculatus (C. L. Koch, 1845) is recorded after 120 years of its last report; newly recorded from Assam, India which extends its distribution from the previously known localities, Java and Sumatra. Platythomisus sudeepi is newly recorded from the Maharashtra State. The variation in the number of abdominal spots on juvenile, sub-adult and adult of P. octomaculatus observed during rearing is reported. Although, the species name 'octomaculatus' suggests eight spots, we observed that the anterior pair of abdominal spots is fused in adults.

Bridging the distributional gap of Tyloridastriata (Thorell, 1877) and new synonymy (Araneae: Tetragnathidae).

BACKGROUND: Although Tyloridastriata has not been reported from India, observations on India Biodiversity Portal (IBP 2015), an open access repository for biodiversity information of Indian subcontinent, showed images resembling this species. The respective locality in Gujarat, India was explored and specimens were studied to confirm record of T.striata in India. Literature study showed some taxonomic lacunae which needed to be resolved. NEW INFORMATION: The tetragnathid spider Tyloridastriata (Thorell, 1877) is redescribed on examination of its long unknown syntypes from Kendari, Southeast Sulawesi deposited in the Natural History Museum of Giacomo Doria, Genoa, Italy and additional material from Kendari and other Indonesian regions. Description of Tyloridastellimicans (Simon, 1885) mentions its identity with T.striata, which however characterizes sub-adult of T.striata and is accordingly synonymized. Tyloridastriata is newly recorded from India which links the distributional gap between China to Australia and Comoros Islands. Distributional and taxonomic records of Tylorida species with T.striata- like globose abdomen infer probable synonymy, which is subject to genus revision.