Genetic analysis of the two zebrafish patched homologues identifies novel roles for the hedgehog signaling pathway.
BACKGROUND
Aberrant activation of the Hedgehog (Hh) signaling pathway in different organisms has shown the importance of this family of morphogens during development. Genetic screens in zebrafish have assigned specific roles for Hh in proliferation, differentiation and patterning, but mainly as a result of a loss of its activity. We attempted to fully activate the Hh pathway by removing both receptors for the Hh proteins, called Patched1 and 2, which are functioning as negative regulators in this pathway.


RESULTS
Here we describe a splice-donor mutation in Ptc1, called ptc1hu1602, which in a homozygous state results in a subtle eye and somite phenotype. Since we recently positionally cloned a ptc2 mutant, a ptc1;ptc2 double mutant was generated, showing severely increased levels of ptc1, gli1 and nkx2.2a, confirming an aberrant activation of Hh signaling. As a consequence, a number of phenotypes were observed that have not been reported previously using Shh mRNA overexpression. Somites of ptc1;ptc2 double mutants do not express anteroposterior polarity markers, however initial segmentation of the somites itself is not affected. This is the first evidence that segmentation and anterior/posterior (A/P) patterning of the somites are genetically uncoupled processes. Furthermore, a novel negative function of Hh signaling is observed in the induction of the fin field, acting well before any of the previously reported function of Shh in fin formation and in a way that is different from the proposed early role of Gli3 in limb/fin bud patterning.


CONCLUSIONS
The generation and characterization of the ptc1;ptc2 double mutant assigned novel and unexpected functions to the Hh signaling pathway. Additionally, these mutants will provide a useful system to further investigate the consequences of constitutively activated Hh signaling during vertebrate development.
Koudijs
Marco J
MJ
Hubrecht Institute, Developmental Biology and Stem Cell Research, Uppsalalaan 8, 3584CT, Utrecht, The Netherlands. m.koudijs@nki.nl
den Broeder
Marjo J
MJ
Groot
Evelyn
E
van Eeden
Fredericus Jm
FJ
D000825:Animal Structures / Q000196:embryology; D000818:Animals; D001483:Base Sequence; D019521:Body Patterning / Q000187:drug effects; D004252:DNA Mutational Analysis; D004625:Embryo, Nonmammalian / Q000002:abnormalities; D005124:Eye Abnormalities / Q000235:genetics; D018507:Gene Expression Regulation, Developmental / Q000187:drug effects; D053823:Hedgehog Proteins / Q000235:genetics / Q000378:metabolism*; D008565:Membrane Proteins / Q000235:genetics*; D008969:Molecular Sequence Data; D050505:Mutant Proteins / Q000378:metabolism; D009154:Mutation / Q000235:genetics; D000072079:Patched Receptors; D000072081:Patched-1 Receptor; D010641:Phenotype; D022821:RNA Splice Sites / Q000235:genetics; D011956:Receptors, Cell Surface / Q000235:genetics*; D017386:Sequence Homology, Amino Acid; D015398:Signal Transduction / Q000187:drug effects; D019170:Somites / Q000002:abnormalities / Q000187:drug effects; D014212:Tretinoin / Q000494:pharmacology; D014704:Veratrum Alkaloids / Q000494:pharmacology; D015027:Zebrafish / Q000196:embryology*; D029961:Zebrafish Proteins / Q000235:genetics*
D053823:Hedgehog Proteins; D008565:Membrane Proteins; D050505:Mutant Proteins; D000072079:Patched Receptors; D000072081:Patched-1 Receptor; D022821:RNA Splice Sites; D011956:Receptors, Cell Surface; D014704:Veratrum Alkaloids; D029961:Zebrafish Proteins; C491715:ptch1 protein, zebrafish; D014212:Tretinoin; C000541:cyclopamine