Left-right asymmetry in BMP4 signalling pathway during chick gastrulation

Determination of the left-right (L-R) axis was shown recently to implicate several genes, among which TGFbeta-related molecules such as Activin betaB, lefty1 and 2 and Nodal. We show here that Bmp4 and its signal transduction pathway partners BMPR IA and Smad1 are transiently expressed on the right side of Hensen's node, when L-R polarity is being established. Moreover, Smad1 is expressed asymmetrically in the nascent notochord. These observations suggest a role for a BMP4-dependent autocrine or paracrine mechanism during early L-R determination.