1. Howard Hughes Medical Institute and Department of Developmental Biology, Stanford University School of Medicine, Stanford, California 94305, USA
2. Department of Pharmacology and Cancer Biology, Duke University Medical Center, Durham, North Carolina 27710, USA
3. Departments of Pathology and Developmental Biology, Stanford University School of Medicine, Stanford, California 94305, USA
4. Department of Cell Biology, The Scripps Research Institute, La Jolla, California 92037, USA

Correspondence to: Roel Nusse¹ Correspondence and requests for materials should be addressed to R.N. (Email: rnusse@cmgm.stanford.edu).

Abstract

Wnt signalling is involved in numerous events in animal development¹, including the proliferation of stem cells² and the specification of the neural crest³. Wnt proteins are potentially important reagents in expanding specific cell types, but in contrast to other developmental signalling molecules such as hedgehog proteins and the bone morphogenetic proteins, Wnt proteins have never been isolated in an active form. Although Wnt proteins are secreted from cells^{4, 5, 6, 7}, secretion is usually inefficient⁸ and previous attempts to characterize Wnt proteins have been hampered by their high degree of insolubility. Here we have isolated active Wnt molecules, including the product of the mouse Wnt3a gene. By mass spectrometry, we found the proteins to be palmitoylated on a conserved cysteine. Enzymatic removal of the palmitate or site-directed and natural mutations of the modified cysteine result in loss of activity, and indicate that the lipid is important for signalling. The purified Wnt3a protein induces self-renewal of haematopoietic stem cells, signifying its potential use in tissue engineering.