The evolution of gnathostome development: Insight from chondrichthyan embryology

The evolution of gnathostome development: Insight from chondrichthyan embryology

J. Andrew Gillis, Neil H. Shubin

Genesis Volume 47 Issue 12, Pages 825 – 841 doi: 10.1002/dvg.20567

The evolution of gnathostome development: Insight from chondrichthyan embryology

The evolution of gnathostome development: Insight from chondrichthyan embryology.

Gillis JA, Shubin NH

Genesis, doi: 10.1002/dvg.20567

Tri-phasic expression of posterior Hox genes during development of pectoral fins in zebrafish: Implications for the evolution of vertebrate paired appendages

Tri-phasic expression of posterior Hox genes during development of pectoral fins in zebrafish: Implications for the evolution of vertebrate paired appendages

Ahn D, Ho RK

Dev Biol (2008 ) Article in press

« D’un coup d’un seul » hein ?

Genetic analysis of the two zebrafish patched homologues identifies novel roles for the hedgehog signaling pathway

Genetic analysis of the two zebrafish patched homologues identifies novel roles for the hedgehog signaling pathway
Marco J Koudijs, Marjo J den Broeder, Evelyn Groot and Fredericus JM van Eeden
BMC Developmental Biology 2008, 8:15doi:10.1186/1471-213X-8-15

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.

Conclusion
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.