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First published online 30 September 2009
doi: 10.1242/dev.038133

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BMP signaling regulates sympathetic nervous system development through Smad4-dependent and -independent pathways

¹ Department of Cell and Molecular Biology, Tulane University, New Orleans, LA 70118, USA.
² Genetics of Development and Disease Branch, NIDDK, NIH, Bethesda, MD 20892, USA.
³ Imperial College London, Faculty of Medicine, London SW7 2AZ, UK.
⁴ Department of Biologic and Materials Sciences, University of Michigan School of Dentistry, Ann Arbor, MI 48109, USA.
⁵ Departments of Pathology and Cell Biology, Columbia University, New York, NY 10032, USA.

^* Author for correspondence (pcserj{at}tulane.edu)

Accepted 26 August 2009

Induction of the sympathetic nervous system (SNS) from its neural crest (NC) precursors is dependent on BMP signaling from the dorsal aorta. To determine the roles of BMP signaling and the pathways involved in SNS development, we conditionally knocked out components of the BMP pathways. To determine if BMP signaling is a cell-autonomous requirement of SNS development, the Alk3 (BMP receptor IA) was deleted in the NC lineage. The loss of Alk3 does not prevent NC cell migration, but the cells die immediately after reaching the dorsal aorta. The paired homeodomain factor Phox2b, known to be essential for survival of SNS precursors, is downregulated, suggesting that Phox2b is a target of BMP signaling. To determine if Alk3 signals through the canonical BMP pathway, Smad4 was deleted in the NC lineage. Loss of Smad4 does not affect neurogenesis and ganglia formation; however, proliferation and noradrenergic differentiation are reduced. Analysis of transcription factors regulating SNS development shows that the basic helix-loop-helix factor Ascl1 is downregulated by loss of Smad4 and that Ascl1 regulates SNS proliferation but not noradrenergic differentiation. To determine if the BMP-activated Tak1 (Map3k7) pathway plays a role in SNS development, Tak1 was deleted in the NC lineage. We show that Tak1 is not involved in SNS development. Taken together, our results suggest multiple roles for BMP signaling during SNS development. The Smad4-independent pathway acts through the activation of Phox2b to regulate survival of SNS precursors, whereas the Smad4-dependent pathway controls noradrenergic differentiation and regulates proliferation by maintaining Ascl1 expression.

Key words: BMP, Neural crest, Smad4 independent, Mouse

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