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# MafB Is Required for Islet β Cell Maturation

Isabella Artner, Bruno Blanchi, Jeffrey C. Raum, Min Guo, Tomomi Kaneko, Sabine Cordes, Michael Sieweke and Roland Stein
Proceedings of the National Academy of Sciences of the United States of America
Vol. 104, No. 10 (Mar. 6, 2007), pp. 3853-3858
Stable URL: http://www.jstor.org/stable/25426746
Page Count: 6
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## Abstract

Pancreatic endocrine cell differentiation depends on transcription factors that also contribute in adult insulin and glucagon gene expression. Islet cell development was examined in mice lacking MafB, a transcription factor expressed in immature α (glucagon⁺) and β (insulin⁺) cells and capable of activating insulin and glucagon expression in vitro. We observed that ${\rm MafB}^{-/-}$ embryos had reduced numbers of insulin⁺ and glucagon⁺ cells throughout development, whereas the total number of endocrine cells was unchanged. Moreover, production of insulin⁺ cells was delayed until embryonic day (E) 13.5 in mutant mice and coincided with the onset of MafA expression, a MafB-related activator of insulin transcription. MafA expression was only detected in the insulin⁺ cell population in MafB mutants, whereas many important regulatory proteins continued to be expressed in insulin⁻ β cells. However, Pdx1, Nkx6.1, and GLUT2 were selectively lost in these insulin-deficient cells between E15.5 and E18.5. MafB appears to directly regulate transcription of these genes, because binding was observed within endogenous control region sequences. These results demonstrate that MafB plays a previously uncharacterized role by regulating transcription of key factors during development that are required for the production of mature α and β cells.

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