Current Biology
Volume 5, Issue 7, July 1995, Pages 791-796
Journal home page for Current Biology

Research Paper
Limb-patterning activity and restricted posterior localization of the amino-terminal product of Sonic hedgehog cleavage

https://doi.org/10.1016/S0960-9822(95)00156-4Get rights and content
Under a Creative Commons license
open archive

Abstract

Background:Sonic hedgehog (Shh), a vertebrate homolog of the Drosophila segment polarity gene hedgehog (hh), has been implicated in patterning of the developing chick limb. Such a role is suggested by the restricted expression of Shh along the posterior limb bud margin, and by the observation that heterologous cells expressing Shh have limb-polarizing activity resembling that of cells from the polarizing region of the posterior limb bud margin. It has not been demonstrated, however, that the Sonic hedgehog protein (SHH) alone is sufficient for limb patterning. SHH has been shown to undergo autoproteolytic cleavage in vitro, yielding two smaller products. It is of interest, therefore, to determine whether processing of SHH occurs in the developing limb and how such processing influences the function of SHH.

Results We demonstrate that SHH is proteolytically processed in developing chick limbs. Grafts of cells expressing SHH protein variants that correspond to individual cleavage products demonstrate that the ability to induce patterned gene expression and to impose morphological pattern upon the limb bud is limited to the amino-terminal product (SHH-N) of SHH proteolytic cleavage. We also demonstrate that bacterially synthesized and purified SHH-N, released from implanted beads, is sufficient for limb-patterning activity. Finally, we show that the endogenous amino-terminal cleavage product is tightly localized to the posterior margin of the limb bud.

Conclusion Our data show that, of the two cleavage products resulting from SHH autoproteolysis, SHH-N expressed in grafted heterologous cells or supplied in purified form is sufficient to impose pattern upon the developing limb. Moreover, the restricted localization of the endogenous amino-terminal SHH cleavage product to the posterior border of the chick limb bud makes it unlikely that its patterning activity results from it being distributed in a broad gradient across the antero-posterior axis. More consistent with the observed localization is a model in which the amino-terminal SHH cleavage product exerts its patterning effects by local induction in or near the polarizing region, initiating a cascade of gene expression that ultimately extends across the developing limb.

Cited by (0)

Alric López-Martínez, B. Kay Simandl and John F. Fallon, Department of Anatomy and Neuroscience, University of Wisconsin, Madison, 1300 University Avenue, Madison, Wisconsin 53706, USA.

David T.Chang, Chin Chiang, Jeffery A. Porter and Philip A. Beachy, Howard Hughes Medical Institute, Department of Molecular Biology and Genetics, The Johns Hopkins School of Medicine, Baltimore, Maryland 21205, USA.

María A.Ros, Departamento de Anatomía y Biología Celular, Universidad de Cantabria, 39011 Santander, Spain.

Alric López-Martínez, David T.Chang, Chin Chiang and Jeffery A. Porter contributed equally to this work.

Correspondence to: John F. Fallon or Philip A. Beachy.