Genomic insights into the Ixodes scapularis tick vector of Lyme disease

Abstract

Ticks transmit more pathogens to humans and animals than any other arthropod. We describe the 2.1 Gbp nuclear genome of the tick, Ixodes scapularis (Say), which vectors pathogens that cause Lyme disease, human granulocytic anaplasmosis, babesiosis and other diseases. The large genome reflects accumulation of repetitive DNA, new lineages of retro-transposons, and gene architecture patterns resembling ancient metazoans rather than pancrustaceans. Annotation of scaffolds representing ∼57% of the genome, reveals 20,486 protein-coding genes and expansions of gene families associated with tick–host interactions. We report insights from genome analyses into parasitic processes unique to ticks, including host ‘questing', prolonged feeding, cuticle synthesis, blood meal concentration, novel methods of haemoglobin digestion, haem detoxification, vitellogenesis and prolonged off-host survival. We identify proteins associated with the agent of human granulocytic anaplasmosis, an emerging disease, and the encephalitis-causing Langat virus, and a population structure correlated to life-history traits and transmission of the Lyme disease agent.

Clonal genome evolution and rapid invasive spread of the marbled crayfish

“…After contig assembly, scaffolding and gap filling, we generated a draft genome sequence with a total length of 3.3 Gb and a weighted mean sequence length (N50) of 39.4 kilobases (kb). Benchmarking with universal single-copy orthologues 25 suggested that the quality of the marbled crayfish genome assembly was comparable to other, recently published arthropod genomes [26][27][28] ( Supplementary Fig. 2).…”

RNA-seq analyses of the midgut from blood- and serum-fed Ixodes ricinus ticks

“…Here, we have shown that two contigs (Ir-114935 and Ir-113744) were up-regulated upon blood-feeding. BLAST analysis of these sequences against the available I. scapularis genome18 revealed that Ir-113744 is most likely an intron-containing version of Ir-114935, which might have originated from pre-mRNA co-isolation.…”

Parasite Cathepsin D-Like Peptidases and Their Relevance as Therapeutic Targets

“…In ticks, the first indication of multi-enzyme CA-based digestion [43] was confirmed by a complex approach in Ixodes ricinus [9,44] and by the recently published tick genome [45]. Midgut APD endopeptidase activity initially cleaves host hemoglobin into large fragments, with a high turnover rate [44], but it does not appear to play the same role in albuminolysis [46].…”