Coordinated control of cell adhesion, polarity, and cytoskeleton underlies Hox-induced organogenesis in Drosophila.
BACKGROUND
Hox genes control animal body plans by directing the morphogenesis of segment-specific structures. As transcription factors, HOX proteins achieve this through the activation of downstream target genes. Much research has been devoted to the search for these targets and the characterization of their roles in organogenesis. This has shown that the direct targets of Hox activation are often transcription factors or signaling molecules, which form hierarchical genetic networks directing the morphogenesis of particular organs. Importantly, very few of the direct Hox targets known are "realizator" genes involved directly in the cellular processes of organogenesis.


RESULTS
Here, we describe for the first time a complete network linking the Hox gene Abdominal-B to the realizator genes it controls during the organogenesis of the external respiratory organ of the larva. In this process, Abdominal-B induces the expression of four intermediate signaling molecules and transcription factors, and this expression results in the mosaic activation of several realizator genes. The ABD-B spiracle realizators include at least five cell-adhesion proteins, cell-polarity proteins, and GAP and GEF cytoskeleton regulators. Simultaneous ectopic expression of the Abd-B downstream targets can induce spiracle-like structure formation in the absence of ABD-B protein.


CONCLUSIONS
Hox realizators include cytoskeletal regulators and molecules required for the apico-basal cell organization. HOX-coordinated activation of these realizators in mosaic patterns confers to the organ primordium its assembling properties. We propose that during animal development, Hox-controlled genetic cascades coordinate the local cell-specific behaviors that result in organogenesis of segment-specific structures.
Lovegrove
Bridget
B
Department of Zoology, University of Cambridge, Cambridge CB2 3EJ, United Kingdom.
Simões
Sergio
S
Rivas
María Luisa
ML
Sotillos
Sol
S
Johnson
Kevin
K
Knust
Elisabeth
E
Jacinto
Antonio
A
Hombría
James Castelli-Gair
JC
D000818:Animals; D001665:Binding Sites / Q000235:genetics; D002448:Cell Adhesion / Q000502:physiology*; D016764:Cell Polarity / Q000502:physiology*; D003599:Cytoskeleton / Q000502:physiology*; D017931:DNA Primers; D004330:Drosophila / Q000254:growth & development*; D029721:Drosophila Proteins / Q000378:metabolism*; D018507:Gene Expression Regulation, Developmental / Q000502:physiology*; D018398:Homeodomain Proteins / Q000378:metabolism*; D007814:Larva / Q000254:growth & development; D016297:Mutagenesis, Site-Directed; D038081:Organogenesis / Q000502:physiology*; D034622:RNA Interference; D015398:Signal Transduction / Q000502:physiology*
C062393:Abd-B proteins, Drosophila; D017931:DNA Primers; D029721:Drosophila Proteins; D018398:Homeodomain Proteins