Type IIA Procollagen as a Modulator of Nodal Signaling

Abstract

Embryonic development depends on the provision of morphogenetic instructions which are generated by signaling factors such as those of the transforming growth factor-beta (TGF-β) superfamily, that cells receive from their neighbours. These instructions contribute towards the determination of cell lineage and differentiation, tissue growth and tissue patterning in the primary body axes. There is increasing evidence that components of the extracellular matrix (ECM) plays a role in modulating signaling activity and morphogen gradients by the sequestration and activation of growth factors. Nodal is a member of the TGFβ family that plays crucial roles in mesendoderm formation and left-right patterning during early vertebrate development. Type IIA procollagen (IIA) is an isoform of type II procollagen, an ECM protein that has been demonstrated to bind to BMPs 2, 4, and 7 and TGFβ1 in vitro and was reputed to antagonize BMP signaling in Xenopus embryos. It has been proposed that IIA may regulate early embryonic patterning as a regulator either by facilitation or by inhibition via binding to growth factors or signaling molecules. Here we show that IIA may act as a facilitator of nodal signaling. In mice lacking IIA we found the expression of Nodal and its signaling downstream targets such as Nodal itself and Pitx2 were either altered or dramatically reduced in the node and left lateral plate mesoderm (LPM). To understand the role of IIA in nodal signaling, we tested for direct interaction between IIA and nodal. By in vitro transfection assays and co-immunoprecipitation assays, we have found that IIA can bind nodal and is a facilitator of nodal signaling. Our results reveal a potential role for IIA in regulating embryonic patterning by facilitating Nodal signaling.