Student Theses and Dissertations

Grace Teng

Date of Award

2009

Document Type

Thesis

RU Laboratory

Papavasiliou Laboratory

Keywords

microRNA, B lymphocytes, somatic gene diversification, activation-induced cytidine deaminase (AID), miR-155

Abstract

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 “classical” 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 3’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 – 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 – small RNA regulation and somatic gene diversification – converging to generate a physiologically beneficial response.

Comments

A thesis presented to the faculty of The Rockefeller University in partial fulfillment of the requirements for the degree of Doctor of Philosophy.

Permanent URL

http://hdl.handle.net/10209/516

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