['Bone morphogenetic protein (BMP) signalling plays a key role in regulating the development of the atrioventricular (AV) septum and valves; however, the molecules that mediate the complex activities of BMP signalling are not fully understood. The major goal of this study is to identify the critical downstream regulatory targets of BMP signalling in AV cushions, which are precursors of the AV septum and valves.', 'We established a conditional immortal AV cushion mesenchymal cell line, tsA58-AVM. Using this line, we observed that the expression of Sema6D is upregulated by BMP stimulation through microarray analysis. Sema6D is required for BMP-upregulated migration of tsA58-AVM cells. To reveal the in vivo role of Sema6D, we established the Sema6D'] Does sema6D act downstream of bone morphogenetic protein signalling to promote atrioventricular cushion development in mice?