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Copyright © 2012 by the National Academy of Sciences.
Hedgehog-responsive mesenchymal clusters direct patterning and emergence of intestinal villiKatherine D. Waltona,1, Åsa Kolteruda,b,1, Michael J. Czerwinskia, Michael J. Bella,c, Ajay Prakasha, Juhi Kushwahaa, Ann S. Grossea, Santiago Schnellc, and Deborah L. Gumucioa,2 aDepartment of Cell and Developmental Biology, University of Michigan Medical School, Ann Arbor, MI 48109; bDepartment of Biosciences and Nutrition, Karolinska Instituet, Novum, SE-141 83 Huddinge, Sweden; and cDepartment of Molecular and Integrative Physiology, Department of Computational Medicine and Bioinformatics, and Brehm Center for Diabetes Research, University of Michigan Medical School, Ann Arbor, MI 48105 Edited by Brigid L. M. Hogan, Duke University Medical Center, Durham, NC, and approved August 2, 2012 (received for review April 4, 2012)
Abstract: In the adult intestine, an organized array of finger-like projections, called villi, provide an enormous epithelial surface area for absorptive function. Villi first emerge at embryonic day (E) 14.5 from a previously flat luminal surface. Here, we analyze the cell biology of villus formation and examine the role of paracrine epithelial Hedgehog (Hh) signals in this process. We find that, before villus emergence, tight clusters of Hh-responsive mesenchymal cells form just beneath the epithelium. Cluster formation is dynamic; clusters first form dorsally and anteriorly and spread circumferentially and posteriorly. Statistical analysis of cluster distribution reveals a patterned array; with time, new clusters form in spaces between existing clusters, promoting approximately four rounds of villus emergence by E18.5. Cells within mesenchymal clusters express Patched1 and Gli1, as well as Pdgfrα, a receptor previously shown to participate in villus development. BrdU-labeling experiments show that clusters form by migration and aggregation of Hh-responsive cells. Inhibition of Hh signaling prevents cluster formation and villus development, but does not prevent emergence of villi in areas where clusters have already formed. Conversely, increasing Hh signaling increases the size of villus clusters and results in exceptionally wide villi. We conclude that Hh signals dictate the initial aspects of the formation of each villus by controlling mesenchymal cluster aggregation and regulating cluster size.
Key Words: epithelial–mesenchymal cross-talk • field pattern • villus morphogenesis
Author contributions: K.D.W., A.K., and D.L.G. designed research; K.D.W., A.K., M.J.C., J.K., and A.S.G. performed research; K.D.W., M.J.B., A.P., and S.S. contributed new reagents/analytic tools; K.D.W., A.K., M.J.C., M.J.B., A.P., S.S., and D.L.G. analyzed data; and K.D.W. and D.L.G. wrote the paper. 1K.D.W. and A.K. contributed equally to this work. The authors declare no conflict of interest. This article is a PNAS Direct Submission. This article contains supporting information online at www.pnas.org/lookup/suppl/doi:10.1073/pnas.1205669109/-/DCSupplemental. 2To whom correspondence should be addressed. E-mail: dgumucio{at}med.umich.edu.
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