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Wnt proteins are lipid-modified and can act as stem cell growth factors


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 cells4,5,6,7, 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.

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Figure 1: Wnt3a and Drosophila Wnt8 purification.
Figure 2: Wnt proteins are palmitoylated on an essential cysteine.
Figure 3: HSCs maintain self-renewing fate with reduced differentiation in response to purified Wnt3a.

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We are grateful to C.-h. Wu for generating the S2 cells expressing Drosophila Wnt8; M. Silverman for help in the C57MG cell transformation assay; and S. Anderson for advice on mass spectrometry. Xenopus embryos were provided by J. Baker and A. Borchers. A. Gilman provided APT-1, and A. Martinez-Arias the wgS21 stock. J. Nelson and members of our laboratories provided comments on the manuscript. This work was supported by Howard Hughes Medical Institute and a NIH grant awarded to T.R. R.N. is an investigator of the Howard Hughes Medical Institute.

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Correspondence to Roel Nusse.

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Willert, K., Brown, J., Danenberg, E. et al. Wnt proteins are lipid-modified and can act as stem cell growth factors. Nature 423, 448–452 (2003).

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