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E Giniger

Publications and source records attributed to E Giniger.

18 recordsLinked to original sources
PubMed2000

The Drosophila Netrin receptor Frazzled guides axons by controlling Netrin distribution.

Netrin is a secreted protein that can act as a chemotropic axon guidance cue. Two classes of Netrin receptor, DCC and UNC-5 (refs 6-9), are required for axon guidance and are thought to mediate Netrin signals in growth cones through their cytoplasmic domains. However, in the guidance of Drosophila photoreceptor axons, the DCC orthologue Frazzled is required not in the photoreceptor neurons but instead in their targets, indicating that Frazzled also has a non-cell-autonomous function. Here we show that Frazzled can capture Netrin and 'present' it for recognition by other receptors. Moreover, Frazzled itself is actively localized within the axon through its cytoplasmic domain, and thereby rearranges Netrin protein into a spatial pattern completely different from the pattern of Netrin gene expression. Frazzled-dependent guidance of one pioneer neuron in the central nervous system can be accounted for solely on the basis of this ability of Frazzled to control Netrin distribution, and not by Frazzled signalling. We propose a model of patterning mechanism in which a receptor rearranges secreted ligand molecules, thereby creating positional information for other receptors.

Amino Acid Sequence↗
PubMed2000

The cyclin-dependent kinase Cdk5 controls multiple aspects of axon patterning in vivo.

Cyclin-dependent kinase 5 (Cdk5) is one of a subfamily of Cdks involved in the control of cell differentiation and morphology rather than cell division. Specifically, Cdk5 and its activating subunit, p35, have been implicated in growth cone motility during axon extension. Both Cdk5 and p35 are expressed in post-mitotic neurons and are localized to growth cones [1] [2] [3] [4]. The Cdk5-p35 complex interacts with the Rac GTPase, a protein required for growth cone motility [5]. Studies using cultured neurons have suggested that Cdk5 activity controls the efficiency of neurite extension [3] [4]. Mutant mice lacking p35 exhibit subtle axon-guidance defects [6], but these mice have severe defects in neuronal migration [6] [7] [8], making it difficult to define precisely the role of the Cdk5-p35 complex in vivo. Here, we examined Cdk5 function in axon patterning in the Drosophila embryo. Although our data support the idea that Cdk5-p35 is involved in axonogenesis, they do not support the view that Cdk5 simply promotes growth cone motility. Instead, we found that disrupting Cdk5 function caused widespread errors in axon patterning.

Animals↗
PubMed1999

LOLA has the properties of a master regulator of axon-target interaction for SNb motor axons of Drosophila.

The proper pathfinding and target recognition of an axon requires the precisely choreographed expression of a multitude of guidance factors: instructive and permissive, positive and negative, and secreted and membrane bound. We show here that the transcription factor LOLA is required for pathfinding and targeting of the SNb motor nerve in Drosophila. We also show that lola is a dose-dependent regulator of SNb development: by varying the expression of one lola isoform we can progressively titrate the extent of interaction of SNb motor axons with their target muscles, from no interaction at all, through wild-type patterning, to apparent hyperinnervation. The phenotypes we observe from altered expression of LOLA suggest that this protein may help orchestrate the coordinated expression of the genes required for faithful SNb development.

Animals↗
PubMed1998

Multiple roles for notch in Drosophila myogenesis.

Notch plays a role in many cell fate decisions in the developing Drosophila embryo, often at successive stages during the formation of a single tissue. In the embryonic mesoderm, Notch is involved in the process by which muscle progenitors are selected from a field of equivalent myoblasts. We have investigated the roles of Notch in somatic myogenesis and show that Notch can affect at least two additional steps in muscle development. Subsequent to the initial specification of progenitors, myoblast identity remains sensitive to mesodermal Notch activity until the time of fusion. Additionally, Notch is capable of suppressing muscle development nonautonomously by regulating a signal that emanates from the ectoderm.

Animals↗
PubMed1998

A role for Abl in Notch signaling.

Abl is an axonal tyrosine kinase that has yet to be clearly linked to a receptor; Notch is a receptor for which the signaling pathway remains incompletely understood. We show here that Notch and abl mutations interact synergistically to produce synthetic lethality and defects in axon extension. Surprisingly, we cannot account for these axonal aberrations on the basis of changes in cell identity. We show, moreover, that Notch is present in the growth cones of extending axons, and that the Abl accessory protein Disabled binds to a signaling domain of Notch in vitro. We therefore speculate that Disabled and Abl may play a role in Notch signaling in Drosophila axons, perhaps by binding to the Notch intracellular domain.

Animals↗
PubMed1996

Expression of constitutively active Notch arrests follicle cells at a precursor stage during Drosophila oogenesis and disrupts the anterior-posterior axis of the oocyte.

During early development, there are numerous instances where a bipotent progenitor divides to give rise to two progeny cells with different fates. The Notch gene of Drosophila and its homologues in other metazoans have been implicated in many of these cell fate decisions. It has been argued that the role of Notch in such instances may be to maintain cells in a precursor state susceptible to specific differentiating signals. This has been difficult to prove, however, due to a lack of definitive markers for precursor identity. We here perform molecular and morphological analyses of the roles of Notch in ovarian follicle cells during Drosophila oogenesis. These studies show directly that constitutively active Notch arrests cells at a precursor stage, while the loss of Notch function eliminates this stage. Expression of moderate levels of activated Notch leads to partial transformation of cell fates, as found in other systems, and we show that this milder phenotype correlates with a prolonged, but still transient, precursor stage. We also find that expression of constitutively active Notch in follicle cells at later stages leads to a defect in the anterior-posterior axis of the oocyte.

Animals↗
PubMed1994

Transient posterior localization of a kinesin fusion protein reflects anteroposterior polarity of the Drosophila oocyte.

BACKGROUND: During oogenesis in Drosophila, determinants that will dictate abdomen and germline formation are localized to the 'polar plasm' in the posterior of the oocyte. Assembly of the polar plasm involves the sequential localization of several messenger RNAs and proteins to the posterior of the oocyte, beginning with the localization of oskar mRNA and Staufen protein during stages 8 and 9 of oogenesis. The mechanism by which these two early components accumulate at the posterior is not known. We have investigated whether directed transport along microtubules could be used to accomplish this localization. RESULTS: We have made a fusion protein composed of the bacterial beta-galactosidase enzyme as a reporter, joined to part of the plus-end-directed microtubule motor, kinesin, and have found that the fusion protein transiently localizes to the posterior of the oocyte during stages 8 and 9 of oogenesis. Treatment with the microtubule-depolymerizing agent colchicine prevents both the localization of the fusion protein and the posterior transport of oskar mRNA and Staufen protein. Furthermore, the fusion protein localizes normally in oocytes mutant for either oskar and staufen, but not in other mutants in which oskar mRNA and Staufen protein are mislocalized. CONCLUSIONS: Association with a plus-end-directed microtubule motor can promote posterior localization of a reporter protein during oogenesis. The genetic requirements for this localization and its sensitivity to colchicine, both of which are shared with the posterior transport of oskar mRNA and Staufen protein, suggest that similar mechanism may function in both processes.

Adenosine Triphosphate↗
PubMed1994

lola encodes a putative transcription factor required for axon growth and guidance in Drosophila.

Mutations in the gene longitudinals lacking (lola) lead to defects in the development of axon tracts in the Drosophila embryonic central nervous system. We now show that lola mutations also cause defects of axon growth and guidance in the peripheral nervous system, and causes a particular cluster of embryonic sense organs (lch5) to be oriented improperly. Axonal aberrations caused by lola are similar to those caused by mutations of three other genes, logo, Notch and Delta, raising the possibility that lola works in the same genetic pathway as do these other molecules. The lola gene encodes at least two nuclear protein products, apparently by differential RNA splicing. The predicted proteins contain an amino-terminal motif similar to that recently described for a family of transcription factors, including the products of the Drosophila genes tramtrack and the Broad Complex. Like Ttk and BR-C, one of the two characterized products of the lola locus bears sequences similar to the zinc-finger motif, but the other (neuronal) form of the protein has no recognizable DNA-binding motif.

Amino Acid Sequence↗
PubMed1993

Specifying the path of the intersegmental nerve of the Drosophila embryo: a role for Delta and Notch.

The intersegmental nerve (ISN) of the Drosophila embryo follows a reproducible course near the anterior border of each segment. Based on the experiments reported here, we suggest that growth of the axons constituting the nerve is guided, in part, by the transmembrane proteins Delta and Notch. In particular, we suggest that expression of Delta protein on a branch of the trachea provides a path for the nerve through the lateral part of the embryo, and that the growing axons use the Notch protein on their surfaces to recognize this path. Consistent with this idea, we show that disruption of the trachea abolishes the ability of the ISN to extend through this part of the embryonic periphery. Finally, we argue that the same regulatory network that directs these peripheral axons also specifies the trajectory of part of the axonal scaffold of the central nervous system.

Animals↗
PubMed1988

GAL4 activates transcription in Drosophila.

GAL4 is a yeast regulatory protein that binds to specific sites within a DNA sequence called UASG (galactose upstream activating sequence) and activates transcription of linked genes. This activation requires two functions of the protein: a DNA binding domain located near the amino terminus, and one or more 'activating regions'. The 'activating regions' are highly acidic (see also ref. 12) and can be replaced, for example, by a short peptide designed to form a negatively charged, amphipathic alpha-helix. GAL4, as well as deletion derivatives bearing one or more 'activating regions' attached to the DNA binding domain, activates transcription in cultured mammalian cells from mammalian promoters linked to a UASG (refs 14, 15). Here we show that GAL4, when expressed in particular tissues of Drosophila larvae, stimulates tissue-specific transcription of a Drosophila promoter linked to GAL4 binding sites.

Animals↗
PubMed1988

Cooperative DNA binding of the yeast transcriptional activator GAL4.

The yeast transcriptional regulatory protein GAL4 binds to four sites in the GAL upstream activating sequence and stimulates transcription of the adjacent GAL1 and GAL10 genes. We show here that binding to at least two of these sites is cooperative in vivo. We also measure stimulation of transcription by pairs of GAL4 binding sites and find that the activities of low-affinity binding sites combine synergistically, whereas the activities of high-affinity binding sites combine only additively. We suggest that the synergistic transcriptional stimulatory activity of the naturally occurring GAL4 binding sites is solely a manifestation of cooperative binding of GAL4 protein to DNA and that the activity of a GAL upstream activating sequence is roughly proportional to the number of GAL4 molecules bound.

Binding Sites↗
PubMed1985

Specific DNA binding of GAL4, a positive regulatory protein of yeast.

We show by the following series of experiments that the yeast positive regulatory protein GAL4 binds to four sites in the upstream activating sequence UASG to activate transcription of the adjacent GAL1 and GAL10 genes. GAL4 protein expressed in E. coli protected guanine residues in UASG from methylation by dimethyl sulfate. The same set of protections was seen in vivo in yeast and depended on the GAL4+ allele. This protection pattern is consistent with the idea that GAL4 protein binds to four related 17 bp sequences, each of which displays approximate 2-fold rotational symmetry. A single near-consensus synthetic 17 bp oligonucleotide, installed in front of the yeast GAL1 or CYC1 transcription units, conferred a high level of galactose inducibility upon these genes. Further experiments suggest that one mechanism of glucose repression is inhibition of the binding of GAL4 protein to DNA.

Base Sequence↗
PubMed1981

Calcium-sensitive binding of heavy meromyosin to regulated actin in the presence of ATP.

Regulated actin, F-actin plus troponin-tropomyosin, activates the myosin ATPase in the presence but not in the absence of calcium. Ultracentrifugation has been used to examine the interaction of regulated actin with two proteolytic fragments of myosin, heavy meromyosin (HMM), a two-headed species, and subfragment 1 (S-1), a single head. In the presence of ATP, the association constant (Ka) for the binding of S-1 to regulated actin is approximately 1.5 X 10(4) M-1, whether or not calcium is present. This is true for S-1 with and without the Mr = 19,000 phosphorylatable light chain. These results confirm the observations of Chalovich et al. (Chalovich, J., Chock, P. B., and Eisenberg, E. (1981) J. Biol. Chem. 256, 575-578) and support their suggestion that the inhibition of the regulated actin-activated ATPase of S-1 by removal of calcium does not result from preventing S-1 binding. The binding of HMM to regulated actin in the presence of ATP, however, is calcium sensitive. Removal of calcium results in approximately a 4-fold decrease in Ka, from 1.1 X 10(4) M-1 to 2.5 X 10(3) M-1. The results with HMM are more easily reconciled with the low stiffness of relaxed muscle and suggest a functional difference between S-1 and HMM.

Actins↗
PubMedDate not supplied

Transcription in yeast activated by a putative amphipathic alpha helix linked to a DNA binding unit.

Gene activation by a DNA-binding regulatory protein in yeast requires the protein to have two components: one to recognize a specific DNA sequence and a second, the 'activating region', to interact with a general transcription factor or perhaps with RNA polymerase. The activating regions that have been characterized are acidic, and mutational analysis of one indicates that this acidity is important for activity. Here we report the design of an artificial protein bearing a novel 15-amino acid peptide linked to a DNA binding fragment of the yeast regulatory protein GAL4). The synthetic peptide is acidic and should it form an alpha-helix, that helix would be amphipathic, having one hydrophilic face bearing the acidic residues, and one hydrophobic face. When expressed in yeast, the artificial protein bearing this peptide efficiently activates the GAL1 gene which is ordinarily activated by GAL4. An otherwise identical protein with the novel 15 amino acids in a scrambled order, and which is thus unable to form an amphipathic structure, does not activate GAL1 transcription.

Binding Sites↗