Identification of differentially expressed genes based on antennae RNA-seq analyses in Culex quinquefasciatus and Culex pipiens molestus.

Background: Both Culex quinquefasciatus and Cx. pipiens molestus are sibling species within Cx. pipiens complex. Even though they are hard to distinguish morphologically, they have different physiological behaviors. However, the molecular mechanisms underlying these differences remain poorly understood.

Methods: Transcriptome sequencing was conducted on antennae of two sibling species. The identification of the differentially expressed genes (DEGs) was performed by the software DESeq2. Database for Annotation, Visualization and Integrated Discovery was used to perform GO pathway enrichment analysis. The protein-protein interaction (PPI) network was constructed with Cytoscape software. The hub genes were screened by the CytoHubba plugin and Degree algorithms. The identified genes were verified by quantitative real-time PCR.

Results: Most annotated transcripts (14,687/16,005) were expressed in both sibling species. Among 15 identified odorant-related DEGs, OBP10 was expressed 17.17 fold higher in Cx. pipiens molestus than Cx. quinquefasciatus. Eighteen resistance-related DEGs were identified, including 15 from CYP gene family and three from acetylcholinesterase, in which CYP4d1 was 86.59 fold more highly expressed in C. quinquefasciatus. Three reproductive DEGs were indentified with the expression from 5.01 to 6.55 fold. Among eight vision-related DEGs, retinoic acid receptor RXR-gamma in Cx. pipiens molestus group was more expressed with 214.08 fold. Among the 30 hub genes, there are 10 olfactory-related DEGs, 16 resistance-related DEGs, and four vision-related DEGs, with the highest score hub genes being OBP lush (6041148), CYP4C21 (6044704), and Rdh12 (6043932). The RT-qPCR results were consistent with the transcriptomic data with the correlation coefficient R = 0.78.

Conclusion: The study provided clues that antennae might play special roles in reproduction, drug resistance, and vision, not only the traditional olfactory function. OBP lush, CYP4C21, and Rdh12 may be key hints to the potential molecular mechanisms behind the two sibling species' biological differences.