WEHI PhD Completion Seminar hosted by Professor Aaron Jex

Amrita Vijay

PhD Student – Jex Laboratory, Infection & Global Health division, WEHI

Transcriptomic landscape mapping of ectoparasite Ixodes ricinus: Organ Functions and Endosymbiont Dynamics

 

Davis Auditorium

Join via SLIDO enter code #WEHIphdcompletion

Including Q&A session

Followed by refreshments in Tapestry Lounge

My PhD project addresses key gaps in the biology of the European castor bean tick, Ixodes ricinus, a major vector of Lyme disease, tick-borne encephalitis, and other zoonoses. First, I generated a high-quality hybrid-assembled transcriptome of over 21,000 predicted transcripts (including 19,000 full-length ORFs), enhancing gene models critical for blood feeding, immune modulation, and reproductive success, while overcoming limitations of short-read RNA-Seq—especially in repeat-rich genomic regions—thereby providing more accurate annotations for genes central to ectoparasitic adaptations. Next, I conducted a temporal transcriptomic analysis of the salivary glands during early ("preparatory"), mid ("slow feeding"), and late ("rapid feeding") phases, uncovering metabolic reprogramming, secretory changes, and immune modulation vital to blood meal acquisition and counteract host defences. The stage-specific salivary signatures—spanning anticoagulants, vasodilators, and anti-inflammatory molecules—highlight the “sialome” plasticity that underpins prolonged hematophagy and vector competence. Finally, I investigated the ovary and its resident endosymbiont(“mitobiont”), Candidatus Midichloria mitochondrii, uncovered how feeding-induced transcriptional shifts in ovarian tissue drive oogenesis and embryogenesis. Early engorgement triggers extensive changes in cell fating, extracellular matrix formation, and immune readiness, priming the ovary for fertilisation and embryonic development. In contrast, mid- and late-feeding stages show relatively stable ovarian transcription, suggesting that the ovary is poised for egg maturation and oviposition. Parallel exome capture sequencing of M. mitochondrii transcripts revealed putative Type IV secretion system components, vitamin biosynthesis genes, and pathways for heme and glycolytic cofactor production, suggesting that the bacterium may enhance host energy metabolism, mitigate oxidative stress, and improve nutrient allocation during feeding and egg production. By localising to the mitochondrial intermembrane space, M. mitochondrii may directly facilitate ATP generation or provide metabolic buffering essential for successful embryogenesis.

Collectively, these integrative findings—from a refined, high-quality transcriptome to detailed, organ- and symbiont-specific transcription profiles—offer a comprehensive molecular view of I. ricinus feeding biology, immune evasion, and reproductive fitness. This work lays the groundwork for novel anti-tick strategies that target salivary gland secretome and symbiont-mediated ovarian pathways, ultimately aiming to disrupt the life cycle of one of Europe’s most significant disease vectors.

All welcome!