Gastroenterology

Gastroenterology

Volume 137, Issue 2, August 2009, Pages 618-628
Gastroenterology

Basic—Alimentary Tract
Paracrine Hedgehog Signaling in Stomach and Intestine: New Roles for Hedgehog in Gastrointestinal Patterning

https://doi.org/10.1053/j.gastro.2009.05.002Get rights and content

Background & Aims

Hedgehog signaling is critical in gastrointestinal patterning. Mice deficient in Hedgehog signaling exhibit abnormalities that mirror deformities seen in the human VACTERL (vertebral, anal, cardiac, tracheal, esophageal, renal, limb) association. However, the direction of Hedgehog signal flow is controversial and the cellular targets of Hedgehog signaling change with time during development. We profiled cellular Hedgehog response patterns from embryonic day 10.5 (E10.5) to adult in murine antrum, pyloric region, small intestine, and colon.

Methods

Hedgehog signaling was profiled using Hedgehog pathway reporter mice and in situ hybridization. Cellular targets were identified by immunostaining. Ihh-overexpressing transgenic animals were generated and analyzed.

Results

Hedgehog signaling is strictly paracrine from antrum to colon throughout embryonic and adult life. Novel findings include the following: mesothelial cells of the serosa transduce Hedgehog signals in fetal life; the hindgut epithelium expresses Ptch but not Gli1 at E10.5; the 2 layers of the muscularis externa respond differently to Hedgehog signals; organogenesis of the pyloric sphincter is associated with robust Hedgehog signaling; dramatically different Hedgehog responses characterize stomach and intestine at E16; and after birth, the muscularis mucosa and villus smooth muscle consist primarily of Hedgehog-responsive cells and Hh levels actively modulate villus core smooth muscle.

Conclusions

These studies reveal a previously unrecognized association of paracrine Hedgehog signaling with several gastrointestinal patterning events involving the serosa, pylorus, and villus smooth muscle. The results may have implications for several human anomalies and could potentially expand the spectrum of the human VACTERL association.

Section snippets

Mice

Gli1+/LacZ, Gli2+/LacZ, and Ptch1+/LacZ mice have been described.20, 27, 28, 29 Shh+/LacZ mice were used in a previous study30; their derivation will be described elsewhere (Gonzalez and Kottman, manuscript in preparation). Heterozygous mice were mated with C57Bl/6 mice, and the morning of vaginal plug was counted as embryonic day (E) 0.5. Genotyping was performed as previously described.20, 27, 28, 29, 30 Protocols for X-gal staining, immunostaining, in situ hybridization, quantitative

Results

Although Gli1, Gli2, and Ptch1 are all components of the Hh pathway, they reveal different aspects of the Hh signaling network. Gli1 is a direct target of Hh, and its expression is dependent on active Hh signaling.27 Ptch1 is also an Hh target gene, but its transcription is not solely dependent on Hh. Finally, Gli2 is an important mediator of activation,27 but its expression is not transcriptionally regulated by Hh. Thus, Ptch1LacZ/+ and Gli2LacZ/+ mice indicate cells capable of responding to

Discussion

This analysis of Hh signal response in the developing and mature gastrointestinal tract provides a cellular basis for Hh function in this tissue and suggests new avenues for exploration. Novel findings include the following: (1) shortly after gut tube formation, epithelial cells of the hindgut and tailgut express Ptch1 but not Gli1; (2) serosal cells respond to Hh signals during fetal life; (3) the developing MM contains Hh-responsive cells at P10 and continues to receive Hh signals during

Acknowledgments

Å.K.'s current address is: Karolinska Institutet, Department of Biosciences and Nutrition, Novum, SE-141 57 Huddinge, Sweden.

The authors thank the Organogenesis Morphology Core and the Microscopy and Image Analysis Laboratory for excellent technical support.

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    Conflicts of interest The authors disclose no conflicts.

    Funding Supported by National Institutes of Health grants R01 DK065850 (to D.L.G.) and P01 DK62041 (to D.L.G., J.L.M., and A.A.D.); the Organogenesis Training Program, T32-HD007505 (to W.J.Z., A.S.G., and Å.K.); and the Hematology Training Program, T32-HL07622 (to K.D.W.).

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