[Show abstract][Hide abstract] ABSTRACT: The Roundabout (Robo) receptors have been intensively studied for their role in regulating axon guidance in the embryonic nervous system, whereas a role in dendritic guidance has not been explored. In the adult giant fiber system of Drosophila, we have revealed that ectopic Robo expression can regulate the growth and guidance of specific motor neuron dendrites, whereas Robo2 and Robo3 have no effect. We also show that the effect of Robo on dendritic guidance can be suppressed by Commissureless coexpression. Although we confirmed a role for all three Robo receptors in giant fiber axon guidance, the strong axon guidance alterations caused by overexpression of Robo2 or Robo3 have no effect on synaptic connectivity. In contrast, Robo overexpression in the giant fiber seems to directly interfere with synaptic function. We conclude that axon guidance, dendritic guidance, and synaptogenesis are separable processes and that the different Robo family members affect them distinctly.
Full-text · Article · May 2002 · The Journal of Neuroscience : The Official Journal of the Society for Neuroscience
[Show abstract][Hide abstract] ABSTRACT: Recent studies have shown the small GTPases, Rac1, Rho, and CDC42, to have a role in axon guidance. To assess their participation in synapse assembly and function we have expressed various forms of Drac1 in the giant fiber system of Drosophila. Overexpression of wild-type Drac1 in the giant fiber (GF) lead to a disruption in axonal morphology; axons often terminate prematurely in a large swelling in the target area but lack the normal lateral bend where the synapse with the jump motor neuron would normally be found. Electrophysiological assays revealed longer latencies and lowering following frequencies indicating defects in the synapse between the GF and the tergotrochanteral motor neuron (TTMn). Thickened abnormal GF dendrites were also observed in the brain. Overexpression of the dominant-negative form of Drac1, (N17), resulted in axons that produced extra branches in the second thoracic neuromere (T2); however, the synaptic connection to the TTMn was present and functioned normally. Conversely, expression of the constitutively active form, Drac1(V12), resulted in a complete lack of neurite outgrowth and this was also seen with overexpression of Dcdc42(V12). In the absence of a GF, these flies showed no response in the jump (TTM) or flight (DLM) muscles upon brain stimulation. Taken together these results show that the balance of actin polymerization and depolymerization determines local process outgrowth and thereby synapse structure and function.
No preview · Article · Jan 2001 · Molecular and Cellular Neuroscience
[Show abstract][Hide abstract] ABSTRACT: In Drosophila, the fish-hook (fish) gene encodes a Sox protein essential for embryonic segmentation and nervous system organization. In this study we examined potential functional roles of fish in postembryonic developmental processes, including those involved in adult appendage development. We show here that Fish protein is expressed in discrete patterns in the larval eye-antennal and leg imaginal discs, the central nervous system, the hindgut, and salivary glands. Genetic mosaic studies indicated that fish function is required for the growth or survival of imaginal cells, and the expression of engrailed and wingless. Ectopic expression of Fish protein resulted in severe disruption of adult structures; legs and antennae were truncated and eye formation was suppressed. These morphological defects were correlated with altered expression patterns of the wingless, decapentaplegic, and bric-a-brac genes. Finally, analysis of truncated versions of Fish protein indicated that the HMG domain was sufficient for Fish nuclear localization and that removal of the transcriptional activation domain did not eliminate Fish function. While Sox proteins have been shown to be important for eye and limb formation in vertebrates, these data provide the first evidence for Sox protein functions in appendage development in invertebrates.
Full-text · Article · Feb 2000 · Developmental Biology
[Show abstract][Hide abstract] ABSTRACT: In this study we investigate the gene regulatory functions of Drosophila Fish-hook (Fish), a high mobility group (HMG) Sox protein that is essential for embryonic segmentation. We show that the Fish HMG domain binds to the vertebrate Sox protein consensus DNA binding sites, AACAAT and AACAAAG, and that this binding induces an 85 degrees DNA bend. In addition, we use a heterologous yeast system to show that the NH2-terminal portion of Fish protein can function as a transcriptional activator. Fish directly regulates the expression of the pair rule gene, even-skipped (eve), by binding to multiple sites located in downstream regulatory regions that direct formation of eve stripes 1, 4, 5, and 6. Fish may function along with the Drosophila POU domain proteins Pdm-1 and Pdm-2 to regulate eve transcription, as genetic interactions were detected between fish and pdm mutants. Finally, we determined that Fish protein is expressed in a dynamic pattern throughout embryogenesis, and is present in nuclear and cytoplasmic compartments.
Full-text · Article · Jun 1998 · Mechanisms of Development