Identification of stage-and tissue-specific endogenous tick promoters

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SUMMARY The lack of a promoter-reporter system in ticks makes functional genomics studies challenging. A few exogenous promoters that appear to work in tick cell lines are viral (i.e. CAAG/CMV promoter) and are constitutively expressing. However, not all research questions can be approached by constitutively expressing a gene. It is useful to gain temporal control over gene expression. In eukaryotic cells, nuclear DNA and proteins combine to form chromatin, which then undergoes complex and orderly folding to form chromosomes. For genes to be expressed, chromatin must be in an open conformation. Open chromatin allows regulatory proteins to bind to DNA and regulate DNA function. The assay for transposase-accessible chromatin with high- throughput sequencing (ATAC-seq) enables high-throughput sequencing of open chromatin regions with the help of transposases. ATAC-seq detects chromatin accessibility of related genes and indicates their regulatory mechanisms. Thus, genes with chromatin accessibility in promoters are more likely to be differentially expressed at the mRNA level. Therefore, by combining the power of ATAC-seq to analyze chromatin accessibility in the promoter regions of whole genes in ticks’ tissues and life stages and then screening differentially expressed genes (DEGs) at the mRNA level by transcriptome sequencing technology (RNA-seq), we will obtain temporally and spatially expressed genes and their promoters. Therefore, our hypothesis/ objective is that by combining gene expression (RNAseq) and open chromatin regions using ATACseq (Aim 1), and promoter assays (Aim 2), we will identify constitutive and stage/sex/tissue-specific promoters for gene expression in ticks. Our pioneering work in tick genome sequencing and CRISPR-Cas9-based genome editing has now made tick gene-editing possible and this proposal will further help us improve the gene-editing protocol by developing the promoter-reporter systems that will allow the screening of mutants without the need to sequence every individual.