The Essential whiB2 Transcriptional Network and its Role in Cell Division

Abstract

Mycobacterium tuberculosis (Mtb) is the causative agent of tuberculosis (TB), which causes millions of infections around the world each year. TB infection is treated with antibiotic therapy; however, the emergence of antibiotic resistance limits critical success in controlling the spread of the disease, and we need to develop drugs with novel biological targets. WhiB2 is an essential transcription factor in Mtb and is an appealing potential drug target since there is precedence in current drugs targeting transcription. In Chapter 2, we dissect the function of the essential gene whiB2/whmD and describe its role in cell growth and division. Through RNA-sequencing of our whiB2/whmD depletion strains, we propose a conserved core regulon of 36 genes, 6 of which are essential genes, and we hypothesize they may directly contribute to WhiB2’s role in cell division. We show direct binding of whmD to the upstream region of several genes including sepF, an essential septal factor, and we further explore the possibility of a larger regulatory network including another essential transcription factor MtrA. Besides testing the therapeutic value of a rationally selected essential transcription factor, we also identified genes under abnormal selective pressure among Mtb clinical strains. The rationale was that there may be selection of subtle genomic changes that contribute to drug resistance that are not detectable by standard genome-wide association study (GWAS) methods. In Chapter 3, we perform a mutational density analysis on a set of 710 clinical strains of Mtb and reveal two hypervariable intergenic (IG) regions of Rv0010c and whiB2. While whiB2 SNPs were not significantly associated with drug resistance, SNPs in Rv0010c IG region were associated with low level isoniazid resistance. Taken together, these data provide greater understanding of the role of WhiB2 in the regulation of growth in Mycobacteria. We provide useful evidence for the importance of a mutational density analysis and the insight it can provide into alternative gene regions that may be under selection. The results presented in this thesis provide a basis for future studies on the development of novel antibiotic targets in M. tuberculosis in the hopes of controlling an important global health pathogen.