Chaudhuri, Aadel Ahmed (2012) MicroRNAs 155 and 125b physiologically and pathologically regulate hematopoiesis and immunity. Dissertation (Ph.D.), California Institute of Technology. http://resolver.caltech.edu/CaltechTHESIS:09042011-230002591
MicroRNAs are a class of ~ 22 nucleotide RNA molecules with roles in diverse biological processes. Here I focus on two microRNAs, miR-155 and miR-125b, and reveal pathways by which their dysregulation leads to myeloproliferative disorder (MPD) and leukemia, respectively. I begin by searching for miR-155 target genes relevant to MPD. By writing an algorithm to search microarray data for predicted microRNA target genes, I identified 89 candidate target genes for miR-155 in myeloid cells. Literature search whittled this list down to 11, and one gene among them, SHIP1, turned out to be largely responsible for miR-155’s ability to cause MPD. My focus shifted to miR-125b when I noticed that miR-125b was enriched in macrophages and thus might play important roles in that cell type. Indeed, gain- and loss-of-function experiments indicated that miR-125b is a potent activator of macrophage activation, and I identified IRF4 as the primary target gene in this process. Finally I asked whether miR-125b plays pathophysiological roles in the development of the hematopoietic system. Thus I overexpressed miR-125b in the hematopoietic system and, to my surprise, observed a very aggressive myeloid leukemia capable of infiltrating peripheral organs including the lungs, liver, kidneys and brain. To determine whether miR-125b is physiologically necessary for normal hematopoietic development, I designed a loss-of-function sponge vector that acts as a decoy, attracting the microRNA away from its normal targets. Use of the sponge in the mouse hematopoietic system led to significantly decreased overall hematopoietic ouput, indicating that miR-125b is physiologically required for normal hematopoiesis. Next, I assayed in vitro a panel of miR-125b target genes and saw that one, Lin28, was superior to the rest. Indeed, Lin28 gain- and loss-of-function in vivo recapitulated major aspects of miR-125b loss- and gain-of-function, respectively. Thus I identified Lin28 as a primary target of miR-125b in the hematopoietic system. In summary, my work shows that two microRNAs, miR-155 and miR-125b, physiologically and pathologically control hematopoietic development. I also identify important target genes for each of these microRNAs in their respective disease processes. Indeed, therapeutic targeting of these pathways may prove useful in the treatment of cancer.
|Item Type:||Thesis (Dissertation (Ph.D.))|
|Subject Keywords:||microRNA; hematopoiesis; immune system; macrophage; leukemia; myeloproliferative disorder; hematopoietic stem cell; mir-155; mir-125b|
|Degree Grantor:||California Institute of Technology|
|Thesis Availability:||Public (worldwide access)|
|Defense Date:||8 August 2011|
|Author Email:||a.chaudhuri (AT) gmail.com|
|Default Usage Policy:||No commercial reproduction, distribution, display or performance rights in this work are provided.|
|Deposited By:||Aadel Chaudhuri|
|Deposited On:||12 Jul 2012 20:40|
|Last Modified:||12 Mar 2013 16:39|
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