Role of Bright/ARID3A in mouse development, somatic cell reprogramming, and pluripotency
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Bright/ARID3A was initially discovered for its role in immunoglobulin heavy chain transcription in the mouse. Bright has also been implicated as a target of p53 and as an E2F binding partner. We have previously shown that Bright is necessary for hematopoietic stem cell development in the embryo. In this work, we show that Bright has a much broader role in development than previously appreciated. Loss of Bright in mice usually results in embryonic lethality due to lack of hematopoietic stem cells. Rare survivor mice initially appear smaller in size than either wildtype or heterozygous littermates, but as they age, these differences diminish. We show that adult Bright null mice have age-dependent kidney defects. Previous work in the adult mouse has not indicated a role for Bright in kidney function. We observed an increase in cellular proliferation in Bright null kidneys, indicating a possible mechanism behind our observation. Loss of Bright has recently been implicated in causing developmental plasticity in somatic cells. Our data indicate that loss of Bright is sufficient to fully reprogram mouse embryonic fibroblasts (MEFs) back to a pluripotent state. We term these cells Bright repression induced pluripotent stem cells (BriPS). BriPS derived from Bright knockout MEFs can be stably maintained in standard embryonic stem cell culture conditions: they express pluripotency markers and can form teratomas in vivo. We further viii show that Bright is active during embryonic stem cell differentiation. Bright represses key pluripotency genes, suggesting the mechanism of reprogramming may be Bright’s direct repression of key pluripotency factors in somatic cells. Recent advances in inducing pluripotency in somatic cells (iPS cells) have created a new field of disease modeling, increased our knowledge of how pluripotency is regulated, and introduced the hope that they can be adapted to treat disease. However, current methods for producing iPS involve overexpression of potentially oncogenic transcription factors, leaving a large gap between the lab and the clinic. Our results mark the first demonstration of an alternative method to reprograming somatic cells that is not mediated by overexpression of pluripotency factors.