Gremlin 1 protein (GREM1, isoform-1) belongs to the BMP (bone morphogenetic protein) antagonist family. Gremlin 1 protein binds BMP2, BMP4, BMP7 and other BMP family proteins1 and inhibits receptor binding. It is highly expressed in the small intestine at the base of the intestinal crypts, as are the related proteins, Gremlin 2 and Chordin-like 1. In this niche, they help maintain the stem cell population by inhibiting BMP produced by mesenchymal cells2. Expression of Gremlin 1 protein is also detected in fetal brain and colon, and at lower levels in adult brain, prostate, pancreas and skeletal muscle.
Recombinant human Gremlin 1 protein and other BMP-antagonists, such as Noggin, are used in the derivation, growth and maintenance of organoids from epithelial tissues including intestinal, liver and pancreatic organoids. However, roles for recombinant Gremlin 1 protein in cancer stem cell maintenance in glioblastoma have been suggested3.