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Evolutionarily conserved developmental pathways

Segment polarity: Hedgehog and its targets are phylogenetically conserved

The Segment polarity genesinitiate the subdivision of anterior and posterior compartments in Drosophila segments, and assure the development and maintenance of subcompartment developmental fates. Hedgehog is secreted by the anterior cells of embryonic segments. Hedgehog signals are received by cells in the posterior compartment of the adjacent segment. The Hedgehog receptor is Smoothened; Patched is another membrane protein that modifies Hedgehog signals. The vertebrate homolog of Smoothened has not yet been identified, but Smoothened belongs to the Frizzled family of Serpentine receptors, the same family as Frizzled2, the receptor for Wingless. The transcription factor Cubitus interruptus regulates the Hedgehog targets decapentaplegic, patched and wingless. Although CI homologs have been cloned in vertebrates, it is not yet known whether they are downstream of PKA, the mediator of HH signals in Drosophila.

In vertebrates, Sonic Hedgehog functions as a ventral patterning influence emanating from the notochord, which induces sclerotome and represses dermomyotome in somite differentiation. SHH is implicated in the patterning of the limb bud. SHH and PKA, expressed in feather bud epithelial cells, exhibit antagonistic action to one another during skin morphogenesis.

Drosophila                   Homologs in other species 
----------                   ----------------------------
Hedgehog                     Vertebrates: Sonic Hedgehog, Desert Hedgehog and others 

Smoothened                   Mammalian: ?

Patched                      Vertebrates: Patched

Protein kinase A             Vertebrates: Protein kinase A 

Fused                        Mammalian: no known homolog

Cubitus interruptus          Mammalian: Gli1, Gli2 and Gli3

Decapentaplegic              Xenopus: BMP4                                          Mammalian: BMP2 and BMP4

Wingless                     Vertebrates: Wnt family

Patched (transcriptionally   Vertebrates: Patched
regulated through PKA)

date revised: 13 Oct 96

Developmental Pathways conserved in Evolution

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