The Critical Role of the miR-285–SCP-2 Regulatory Axis in Reproductive Homeostasis of the Hard Tick Haemaphysalis. longicornis

Background Ticks are critical vector organisms, and their reproductive regulatory mechanisms represent potential targets for population control. Sterol carrier protein-2 ( SCP-2 ) plays a vital role in lipid metabolism, yet its function in tick reproduction and its upstream regulatory pathways remain poorly understood. Methods The full-length sequence of the SCP-2 gene was identified and characterized in the hard tick Haemaphysalis. longicornis . Phylogenetic analysis was performed to assess its evolutionary conservation. Spatiotemporal expression of SCP-2 was profiled across developmental stages and tissues. RNA interference (RNAi) was used to knockdown SCP-2 expression, and phenotypic effects on ovarian development and egg production were evaluated. Bioinformatics tools and dual-luciferase reporter assays were employed to identify and validate miR-285 as a regulator targeting the SCP-2 3'UTR. In vivo overexpression of miR-285 was conducted to confirm its functional impact on SCP-2 expression and reproduction. Results Phylogenetic analysis revealed high conservation between H. longicornis SCP-2 and its orthologs in other arachnids. SCP-2 was specifically and highly expressed in ovaries during the late feeding stage. RNAi-mediated knockdown of SCP-2 led to severe ovarian developmental defects, arrested oocyte maturation, and a marked reduction in egg production. MiR-285 was identified as a direct regulator of the SCP-2 3'UTR, and its overexpression in vivo significantly suppressed SCP-2 transcript levels, recapitulating the reproductive impairments observed after SCP-2 knockdown. Conclusions This study is the first to elucidate the essential role of the miR-285– SCP-2 regulatory axis in maintaining reproductive homeostasis in H. longicornis . These findings advance the understanding of reproductive biology in arthropods and provide a theoretical foundation and precise molecular targets for developing novel tick control strategies.