Yesai Sevak Fstkchyan
Published: 2014
Total Pages: 61
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Apolipoprotein B mRNA editing enzyme catalytic polypeptide like-3 G (APOBEC3G) is a member of a family of cytidine deaminases that includes activation-induced deaminase (AID), the enzyme responsible for somatic hypermutation in B cells. While APOBEC3G (A3G) is best known for its activity in restricting both retroviral infection and the mobility of genomic retrotransposable elements, there is mounting evidence that A3G possesses a far more involved role in the cell. A3G has been localized to P-bodies, subcellular foci of mRNA editing and microRNA activity, and has been found to directly influence microRNA activity. The Broad Institute Differentiation Map (dMap) is a collection of microarray data that quantifies levels of gene expression in hematopoietic cells throughout their development. According to dMap, levels of A3G expression fluctuate tremendously throughout the process of hematopoiesis. This is inconsistent with a purely antiretroviral factor. We chose to determine whether A3G may be functionally important in hematopoietic development. Analysis by qRT-PCR of A3G expression at the mRNA level reveals that A3G is expressed in human embryonic stem cells (hESC). Moreover, there is a significant rise in A3G expression when hESCs are induced to differentiate into early hematopoietic progenitors. Together, these data suggest a role for A3G in the earliest stages of human hematopoiesis. While unpublished data from our lab provides evidence that suggests A3G has a role in intermediate hematopoietic lineage commitment, it is unclear how A3G might influence early hematopoietic development. We, therefore, asked whether A3G plays a role in the development of early hematopoietic progenitors derived from hESCs. To address our question, we applied a loss-of-function strategy to investigate whether the absence of A3G might impair or alter early hematopoietic development. To accomplish this, we used hESCs as a model system and knocked down A3G. We then characterized the ability of these genetically altered cells to give rise to early hematopoietic progenitors and their hematopoietic lineage commitment towards terminally differentiated cell types of the blood using flow cytometry and methylcellulose colony forming assays. Results from this study have identified a novel function for A3G in that it influences late progenitor fate decisions, but does not alter early development of hematopoietic progenitors demonstrated by impaired erythropoiesis and increased myelopoiesis. This study has uncovered a novel developmental factor previously not thought to be important in human hematopoietic development.
