Motor axon guidance in Drosophila.

The Drosophila motor system starts to assemble during embryonic development. It is composed of 30 muscles per abdominal hemisegment and 36 motor neurons assembling into nerve branches to exit the CNS, navigate within the muscle field and finally establish specific connections with their target muscles. Several families of guidance molecules that play a role controlling this process as well as transcriptional regulators that program the behavior of specific motor neuron have been identified.

Deconstruction of the beaten Path-Sidestep interaction network provides insights into neuromuscular system development.

An 'interactome' screen of all cell-surface and secreted proteins containing immunoglobulin superfamily (IgSF) domains discovered a network formed by paralogs of Beaten Path (Beat) and Sidestep (Side), a ligand-receptor pair that is central to motor axon guidance. Here we describe a new method for interactome screening, the Bio-Plex Interactome Assay (BPIA), which allows identification of many interactions in a single sample. Using the BPIA, we 'deorphanized' four more members of the Beat-Side network.

Tinman Regulates NetrinB in the Cardioblasts of the Drosophila Dorsal Vessel.

Morphogenesis of the Drosophila dorsal vessel (DV) shares similarities with that of the vertebrate heart. Precursors line up at both sides of the embryo, migrate towards the midline and fuse to form a tubular structure. Guidance receptors and their ligands have been implicated in this process in vertebrates and invertebrates, as have been a series of evolutionarily conserved cardiogenic transcriptional regulators including Tinman, the Drosophila homolog of the transcription factor Nkx-2.

The Unc-5 Receptor Is Directly Regulated by Tinman in the Developing Drosophila Dorsal Vessel.

During early heart morphogenesis cardiac cells migrate in two bilateral opposing rows, meet at the dorsal midline and fuse to form a hollow tube known as the primary heart field in vertebrates or dorsal vessel (DV) in Drosophila. Guidance receptors are thought to mediate this evolutionarily conserved process. A core of transcription factors from the NK2, GATA and T-box families are also believed to orchestrate this process in both vertebrates and invertebrates.

The homeodomain transcription factor Hb9 controls axon guidance in Drosophila through the regulation of Robo receptors.

Transcription factors establish neural diversity and wiring specificity; however, how they orchestrate changes in cell morphology remains poorly understood. The Drosophila Roundabout (Robo) receptors regulate connectivity in the CNS, but how their precise expression domains are established is unknown. Here, we show that the homeodomain transcription factor Hb9 acts upstream of Robo2 and Robo3 to regulate axon guidance in the Drosophila embryo.

A transcription factor network coordinates attraction, repulsion, and adhesion combinatorially to control motor axon pathway selection.

Combinations of transcription factors (TFs) instruct precise wiring patterns in the developing nervous system; however, how these factors impinge on surface molecules that control guidance decisions is poorly understood. Using mRNA profiling, we identified the complement of membrane molecules regulated by the homeobox TF Even-skipped (Eve), the major determinant of dorsal motor neuron (dMN) identity in Drosophila. Combinatorial loss- and gain-of-function genetic analyses of Eve target genes indicate that the integrated actions of attractive, repulsive, and adhesive molecules direct eve-dependent dMN axon guidance.

Transcriptional regulation of guidance at the midline and in motor circuits.

Axon navigation through the developing body of an embryo is a challenging and exquisitely precise process. Axonal processes within the nervous system harbor extremely complicated internal regulatory mechanisms that enable each of them to respond to environmental cues in a unique way, so that every single neuron has an exact stereotypical localization and axonal projection pattern. Receptors and adhesion molecules expressed on axonal membranes will determine their guidance properties.

A GATA/homeodomain transcriptional code regulates axon guidance through the Unc-5 receptor.

Transcription factor codes play an essential role in neuronal specification and axonal guidance in both vertebrate and invertebrate organisms. However, how transcription codes regulate axon pathfinding remains poorly understood. One such code defined by the homeodomain transcription factor Even-skipped (Eve) and by the GATA 2/3 homologue Grain (Grn) is specifically required for motor axon projection towards dorsal muscles in Drosophila.

Protein coadaptation and the design of novel approaches to identify protein-protein interactions.

Proteins rarely function in isolation but they form part of complex networks of interactions with other proteins within or among cells. The importance of a particular protein for cell viability is directly dependent upon the number of interactions where it participates and the function it performs: the larger the number of interactions of a protein the greater its functional importance is for the cell. With the advent of genome sequencing and "omics" technologies it became feasible conducting large-scale searches for protein interacting partners.

The Adam family metalloprotease Kuzbanian regulates the cleavage of the roundabout receptor to control axon repulsion at the midline.

Slits and their Roundabout (Robo) receptors mediate repulsive axon guidance at the Drosophila ventral midline and in the vertebrate spinal cord. Slit is cleaved to produce fragments with distinct signaling properties. In a screen for genes involved in Slit-Robo repulsion, we have identified the Adam family metalloprotease Kuzbanian (Kuz).

The homeobox transcription factor even-skipped regulates netrin-receptor expression to control dorsal motor-axon projections in Drosophila.

Homeobox transcription-factor codes control motor-neuron subtype identity and dorsal versus ventral axon guidance in both vertebrate and invertebrate nervous systems; however, the specific axon guidance-receptors that are regulated by these transcription factors to control pathfinding are poorly defined. In Drosophila, the Even-skipped (Eve) transcription factor specifies dorsal motor-axon projection through the regulation of unidentified guidance molecules. The Netrins and their attractive and repulsive receptors DCC and Unc-5, respectively, define important conserved cue and receptor families that control growth-cone guidance.

Cross GTPase-activating protein (CrossGAP)/Vilse links the Roundabout receptor to Rac to regulate midline repulsion.

The regulators of the Rho-family GTPases, GTPase-activating proteins (GAPs) and guanine exchange factors (GEFs), play important roles in axon guidance. By means of a functional genomic study of the Rho-family GEFs and GAPs in Drosophila, we have identified a Rho-family GAP, CrossGAP (CrGAP), which is involved in Roundabout (Robo) receptor-mediated repulsive axon guidance. CrGAP physically associates with the Robo receptor.

Slit stimulation recruits Dock and Pak to the roundabout receptor and increases Rac activity to regulate axon repulsion at the CNS midline.

Drosophila Roundabout (Robo) is the founding member of a conserved family of repulsive axon guidance receptors that respond to secreted Slit proteins. Here we present evidence that the SH3-SH2 adaptor protein Dreadlocks (Dock), the p21-activated serine-threonine kinase (Pak), and the Rac1/Rac2/Mtl small GTPases can function during Robo repulsion. Loss-of-function and genetic interaction experiments suggest that limiting the function of Dock, Pak, or Rac partially disrupts Robo repulsion.

Discoidin domain receptor 2 regulates fibroblast proliferation and migration through the extracellular matrix in association with transcriptional activation of matrix metalloproteinase-2.

Discoidin domain receptor 2 (DDR2) is a tyrosine kinase receptor expressed in mesenchymal tissues, the ligand of which is fibrillar collagen. We have compared DDR2 signaling in skin fibroblasts derived from DDR2(-/-) and DDR2(+/-) mice. Proliferation of DDR2(-/-) fibroblasts was significantly decreased compared with DDR2(+/-) cells.