Abstract:
Tick saliva helps blood feeding by its antihemostatic and immunomodulatory activities. Tick salivary gland
transcriptomes (sialotranscriptomes) revealed thousands of transcripts coding for putative secreted polypeptides.
Hundreds of these transcripts code for groups of similar proteins, constituting protein families, such as the lipocalins
and metalloproteases. However, while many of these transcriptome-derived protein sequences matches
sequences predicted by tick genome assemblies, the majority are not represented in these proteomes. The diversity
of these transcriptome-derived transcripts could derive from artifacts generated during assembly of short
Illumina reads or derive from polymorphisms of the genes coding for these proteins. To investigate this
discrepancy, we collected salivary glands from blood-feeding ticks and, from the same homogenate, made and
sequenced libraries following Illumina and PacBio protocols, with the assumption that the longer PacBio reads
would reveal the sequences generated by the assembly of Illumina reads. Using both Rhipicephalus zambeziensis
and Ixodes scapularis ticks, we have obtained more lipocalin transcripts from the Illumina library than the PacBio
library. To verify whether these unique Illumina transcripts were real, we selected 9 uniquely Illumina-derived
lipocalin transcripts from I. scapularis and attempted to obtain PCR products. These were obtained and their
sequences confirmed the presence of these transcripts in the I. scapularis salivary homogenate. We further
compared the predicted salivary lipocalins and metalloproteases from I. scapularis sialotranscriptomes with those
found in the predicted proteomes of 3 publicly available genomes of I. scapularis. Results indicate that the
discrepancy between the genome and transcriptome sequences for these salivary protein families is due to a high
degree of polymorphism within these genes.
