title: Crosstalk between Nodal/activin and MAPK p38 signaling is essential for anterior-posterior axis specification.
abstract: Nodal/activin signaling plays a key role in anterior-posterior (A-P) axis formation by inducing the anterior visceral endoderm (AVE), the extraembryonic signaling center that initiates anterior patterning in the embryo. Here we provide direct evidence that the mitogen-activated protein kinase (MAPK) p38 regulates AVE specification through a crosstalk with the Nodal/activin signaling pathway. We show that p38 activation is directly stimulated by Nodal/activin and fails to be maintained upon inhibition of this pathway both in vivo and in vitro. In turn, p38 strengthens the Nodal signaling response by phosphorylating the Smad2 linker region and enhancing the level of Smad2 activation. Furthermore, we demonstrate that this p38 amplification loop is essential for correct specification of the AVE in two ways: first, by showing that inhibiting p38 activity in 5.5 days postcoitum embryo cultures leads to a switch from AVE to an extraembryonic visceral endoderm cell identity, and second, by demonstrating that genetically reducing p38 activity in a Nodal-sensitive background leads to a failure of AVE specification in vivo. Collectively, our results reveal a novel role for p38 in regulating the threshold of Nodal signaling and propose a new mechanism by which A-P axis development can be reinforced during early embryogenesis.
authors.affiliation: Molecular Embryology Group, MRC Clinical Sciences Centre, Faculty of Medicine, Imperial College London, Hammersmith Hospital Campus, London W12 0NN, UK.
authors.forename: Melanie
authors.initials: M
authors.lastname: Clements
authors.forename: Barbara
authors.initials: B
authors.lastname: Pernaute
authors.forename: Francis
authors.initials: F
authors.lastname: Vella
authors.forename: Tristan A
authors.initials: TA
authors.lastname: Rodriguez
mesh_terms: D028341:Activins / Q000378:metabolism*; D000818:Animals; D019521:Body Patterning; D009154:Mutation; D055457:Nodal Protein / Q000378:metabolism*; D010766:Phosphorylation; D015398:Signal Transduction; D048051:p38 Mitogen-Activated Protein Kinases / Q000235:genetics / Q000378:metabolism*
chemical_list: D055457:Nodal Protein; D028341:Activins; D048051:p38 Mitogen-Activated Protein Kinases