TOR as a Regulatory Target in Rhipicephalus microplus Embryogenesis

Area of Science:

• Molecular Biology
• Parasitology
• Tick Biology

Background:

• Embryogenesis requires metabolic control, with insulin signaling regulating glucose homeostasis and reproduction.
• Key insulin pathway targets include protein kinase B (AKT), glycogen synthase kinase 3 (GSK-3), and target of rapamycin (TOR).
• While AKT and GSK-3 roles are known in tick development, TOR's function remains unexplored.

Purpose of the Study:

• Investigate the role of the TOR signaling pathway and its downstream effectors (S6K, 4E-BP1) in tick embryonic development and reproduction.
• Determine if TOR is specifically required for activating its downstream targets in tick cells.
• Assess the potential of TOR as a target for tick control measures.

Main Methods:

• Utilized the BME26 tick embryonic cell line for in vitro studies.
• Administered exogenous insulin and chemical inhibitors (TOR, AKT, GSK-3) to BME26 cells.
• Performed in vivo studies involving TOR double-stranded RNA (dsRNA) injection into female ticks.

Main Results:

• Exogenous insulin stimulated TOR transcription in BME26 cells.
• TOR inhibition decreased cell viability, compromised membrane integrity, and downregulated S6K and 4E-BP1 transcription.
• AKT or GSK-3 inhibition did not affect S6K and 4E-BP1 transcription, indicating TOR's specific role.
• TOR, S6K, and 4E-BP1 transcripts showed varied levels during embryonic development.
• TOR dsRNA injection in females caused delayed oviposition, abnormal egg morphology, reduced vitellin, and lower larval hatching.

Conclusions:

• The TOR signaling pathway is essential for tick reproduction and embryogenesis in *Rhipicephalus microplus*.
• TOR specifically activates its downstream targets S6K and 4E-BP1.
• TOR represents a promising target for developing novel tick control strategies.