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We have identified the Drosophila transmembrane molecule kekkon 1 (kek1) as an inhibitor of the epidermal growth factor receptor (EGFR) and demonstrate that it acts in a negative feedback loop to modulate the activity of the EGFR tyrosine kinase. During oogenesis, kek1 is expressed in response to the Gurken/EGFR signaling pathway, and loss of kek1 activity is associated with an increase in EGFR signaling...
Many neurons in both vertebrates and invertebrates innervate multiple targets by sprouting secondary axon collaterals (or branches) from a primary axon shaft. To begin to identify molecular regulators of axon branch initiation or extension, we studied the growth of single sensory axons in an in vitro collagen assay system and identified an activity in extracts of embryonic spinal cord and of postnatal...
Extending axons in the developing nervous system are guided in part by repulsive cues. Genetic analysis in Drosophila, reported in a companion to this paper, identifies the Slit protein as a candidate ligand for the repulsive guidance receptor Roundabout (Robo). Here we describe the characterization of three mammalian Slit homologs and show that the Drosophila Slit protein and at least one of the...
Hedgehog (Hh) proteins play diverse organizing roles in development by regulating gene expression in responding cells. The Gli homolog Cubitus interruptus (Ci) is involved in controlling the transcription of Hh target genes. A repressor form of Ci arises in the absence of Hh signaling by proteolytic cleavage of intact Ci. We show that this cleavage is essential for limb patterning and is regulated...
The olfactory bulb plays a central role in olfactory information processing through its connections with both peripheral and cortical structures. Axons projecting from the olfactory bulb to the telencephalon are guided by a repulsive activity in the septum. The molecular nature of the repellent is not known. We report here the isolation of vertebrate homologs of the Drosophila slit gene and show that...
Inwardly rectifying potassium channels (K ir ), comprising four subunits each with two transmembrane domains, M1 and M2, regulate many important physiological processes. We employed a yeast genetic screen to identify functional channels from libraries of K ir 2.1 containing mutagenized M1 or M2 domains. Patterns in the allowed sequences indicate that M1 and M2 are helices...
The crystal structure of the complex of ARF1 GTPase bound to GDP and the catalytic domain of ARF GTPase-activating protein (ARFGAP) has been determined at 1.95 Å resolution. The ARFGAP molecule binds to switch 2 and helix α3 to orient ARF1 residues for catalysis, but it supplies neither arginine nor other amino acid side chains to the GTPase active site. In the complex, the effector-binding region...
Polarization of epithelial cells depends on a hierarchical process whereby specific membrane-associated proteins become targeted to specialized membrane domains. Here, we describe a novel Drosophila protein, Discs Lost (DLT), that plays a crucial role in the polarization of embryonic epithelia during cellular blastoderm formation. At subsequent stages of development, DLT interacts with the apical...
Survival factors can suppress apoptosis in a transcription-independent manner by activating the serine/threonine kinase Akt, which then phosphorylates and inactivates components of the apoptotic machinery, including BAD and Caspase 9. In this study, we demonstrate that Akt also regulates the activity of FKHRL1, a member of the Forkhead family of transcription factors. In the presence of survival factors,...
A redacted prion protein (PrP) of 106 amino acids with two large deletions was expressed in transgenic (Tg) mice deficient for wild-type (wt) PrP (Prnp 0/0 ) and supported prion propagation. RML prions containing full-length PrP Sc produced disease in Tg(PrP106)Prnp 0/0 mice after ~300 days, while transmission of RML106 prions containing PrP S ...
Previous studies suggested that Roundabout (Robo) is a repulsive guidance receptor on growth cones that binds to an unknown midline ligand. Here we present genetic evidence that Slit is the midline Robo ligand; a companion paper presents biochemical evidence that Slit binds Robo. Slit is a large extracellular matrix protein expressed by midline glia. In slit mutants, growth cones enter the midline...
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