Date of Award
microRNA, B lymphocytes, somatic gene diversification, activation-induced cytidine deaminase (AID), miR-155
Small regulatory RNAs supplement the canonical pathways of gene regulation through diverse mechanisms of transcriptional, post-transcriptional, and post-translational silencing. These mechanisms range from â€œclassicalâ€ RNA interference (RNAi), to gene repression by microRNAs (miRNAs), to maintenance of genomic stability by repeatassociated small RNAs. Here, I describe the contribution of miRNA-mediated regulation to a specific case of gene expression that requires significant somatic alteration of the genetic code. B lymphocytes perform somatic hypermutation (SHM) and class switch recombination (CSR) of the immunoglobulin locus to generate an antibody repertoire diverse in both affinity and function. These somatic diversification processes are catalyzed by activation-induced cytidine deaminase (AID), a potent DNA mutator whose expression and function are highly regulated. I show that AID is regulated posttranscriptionally by a lymphocyte-specific microRNA, miR-155. I find that miR-155 is upregulated in murine B lymphocytes undergoing CSR, and targets a conserved site in the 3â€™untranslated region of the AID mRNA. Disruption of this target site in vivo results in quantitative and temporal deregulation of AID expression, accompanied by functional consequences for CSR and affinity maturation. Thus, miR-155, which is known to play important roles in regulating the germinal center reaction, does so in part by directly downmodulating AID expression. Using a novel transgenic approach, I have characterized a single miRNA â€“ target pair that has functional implications in adaptive immunity and maintenance of genome integrity. The regulation of AID by miR-155 serves as a striking example of two distinct regulatory mechanisms â€“ small RNA regulation and somatic gene diversification â€“ converging to generate a physiologically beneficial response.
Teng, Grace, "Regulation of Immunoglobulin Gene Diversification By Noncoding RNA's" (2009). Student Theses and Dissertations. 143.