Tsukushi Functions as an Organizer Inducer by Inhibition of BMP Activity in Cooperation with Chordin

Abstract

During chick gastrulation, inhibition of BMP signaling is required for primitive streak formation and induction of Hensen's node. We have identified a unique secreted protein, Tsukushi (TSK), which belongs to the Small Leucine-Rich Proteoglycan (SLRP) family and is expressed in the primitive streak and Hensen's node. Grafts of cells expressing TSK in combination with the middle primitive streak induce an ectopic Hensen's node, while electroporation of TSK siRNA inhibits induction of the node. In Xenopus embryos, TSK can block BMP function and induce a secondary dorsal axis, while it can dorsalize ventral mesoderm and induce neural tissue in embryonic explants. Biochemical analysis shows that TSK binds directly to both BMP and chordin and forms a ternary complex with them. These observations indicate that TSK is an essential dorsalizing factor involved in the induction of Hensen's node.

Nephrocan, a Novel Member of the Small Leucine-rich Repeat Protein Family, Is an Inhibitor of Transforming Growth Factor-β Signaling

“…D, phylogenetic tree analysis of NPN together with other mouse SLRP members. PRELP is proline/arginine-rich end leucine-rich repeat protein; m-TSK is mouse ortholog of tsukushi (35). consistent with its mRNA expression pattern (Fig.…”

“…Some of the SLRP members, e.g. asporin (33), osteoglycin (34), tsukushi (35), and podocan (36), are also known to be glycoproteins but not proteoglycans.…”

Tsukushi functions as a Wnt signaling inhibitor by competing with Wnt2b for binding to transmembrane protein Frizzled4

“…S8 M-Q). Bone morphogenetic protein (BMP) signaling is required for the development of the CB, and we previously showed that TSK can work as a BMP antagonist during early embryonic development (13). However, the expression of TGF-β signaling components in the CB was not obviously changed in TSK −/− mice compared with WT animals (Fig.…”

“…TSK belongs to the group of class IV SLRPs, which includes structurally related chondroadherin (32) and nyctalopin (33), but it shares functional properties with class I SLRPs (34), including their role as BMP inhibitors (13,15). We have previously reported that TSK interacts with BMP ligands and the BMP antagonist chordin and functions as an inhibitor of BMP signaling during gastrula and neurula stages.…”

“…We previously described the isolation of Tsukushi (TSK) protein isoforms (13), soluble molecules belonging to the small leucinerich proteoglycan (SLRP) family (14), and showed that they work as extracellular modulators of pivotal signaling cascades during early embryonic development in chicks and frogs (13,(15)(16)(17). We also observed that TSK rescues Xenopus embryos from the hyperdorsalized effects induced by Wnts (Fig.…”