Prepattern in the developing Drosophila eye revealed by an activated torso--sevenless chimeric receptor (original) (raw)
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Dynamics of Drosophila eye development and temporal requirements of sevenless expression
Development, 1989
The development of the compound eye of Drosophila consists of a linear, stereotyped program starting at the posterior end of the eye imaginal disc and progressing towards the anterior border. The determination of the R7 photoreceptor cells is part of this process and is dependent on the sevenless gene. In this study, we used a heat-shock-inducible sevenless gene as a conditional allele to determine the exact temporal requirements of sevenless gene expression and to reveal the stages of ommatidial development during which the presumptive R7 cell can respond to the presence of sevenless protein. Our results indicate that sevenless gene function is only required during a brief, defined period for the initiation of R7 development; subsequently sevenless is dispensable for both differentiation and function of the R7 photoreceptors. Furthermore, using rescue of R7 cells as an internal marker to monitor the progression of eye development we could examine when and at what rate ommatidial co...
Specification of cell fate in the developing eye ofDrosophila
BioEssays, 1991
Determination of cell fate in the developing eye of Drosophila depends on cellular interactions. In the eye imaginal disc, an initially unpatterned epithelial sheath of cells, single cells are specified in regular intervals to become the R8 photoreceptor cells. Genes such as Notch and scabrous participate in this process suggesting that specification of ommatidial founder cells and the formation of bristles in the adult epidermis involve a similar mechanism known as lateral inhibition. The subsequent steps of ommatidial assembly involve a different mechanism: undetermined cells read their position based on the contacts they make with neighbors that have already begun to differentiate. The development of the R7 photoreceptor cell is best understood. The key role seems to be played by sevenless, a receptor tyrosine kinase on the surface of the R7 precursor. It transmits the positional information-most likely encoded by boss on the neighboring R8 cell membraneinto the cell via its tyrosine kinase that activates a signal transduction cascade. Two components of this cascade-Sos and sina-have been identified genetically, sina encodes a nuclear protein whose expression is not limited to R7. Constitutive activation of the sevenless kinase by overexpression results in the diversion of other ommatidial cells into the R7 pathway, suggesting that activation of the sevenless signalling pathway is sufficient to specify R7 development.
Mechanisms of Development, 1992
Studies on the development of the R7 photoreceptor in the Drosophila eye thus far have identified three genes that specifically affect this cell: sevenless, boss and sina. In each of these mutants the R7 precursor develops instead as the equatorial cone cell (EQC). We have isolated an enhancer trap line, 1-1214, in which fl-galactosidase is primarily expressed in the R7 cell throughout its development. In mutations of sevenless, boss and sina, expression in H214 is initially reduced although still present in the R7 precursor and persists in the EQC into which it develops. The EQC in wild type never expresses /acZ in 1-1214. This result is in contrast to that seen with other enhancer trap lines that display expression in R7, and indicates that some aspect of R7 differentiation is independent of the genetic pathway(s) involving sevenless, boss and sina. Drosophila eye; H214; Positional information; sevenless; bride of sevenless; seven in absentia Correspondence to:
Journal of Cell Science, 1990
Summary In the developing eye of Drosophila cell fate is controlled by a cascade of inductive interactions. Little is known about how the specificity of positional signalling is achieved such that directly adjacent progenitor cells reproducibly choose distinct developmental pathways. The determination of the R7 photoreceptor in each ommatidium depends on the presence of the sevenless protein which acts as a receptor for positional information on the R7 precursor. The rough gene encodes a homeodomain protein that plays an instructive role in the determination of the R3 and R4 photoreceptor cells. The use of ectopic expression of sevenless and rough has provided insight into the mechanisms of positional signalling and the normal function of rough. Ubiquitous expression of sevenless does not alter cell fate suggesting that the inducing signal is both spatially and temporally controlled. Conversely, ectopic expression of rough in the R7 precursor causes a transformation of R7 cells into...
Journal of Cell Science, 2006
How cellular behaviors such as cell-to-cell communication, epithelial organization and cell shape reorganization are coordinated during development is poorly understood. The developing Drosophila eye offers an ideal model system to study these processes. Localized actin polymerization is required to constrict the apical surface of epithelial cells of the eye imaginal disc to maintain the refined arrangement of the developing ommatidia. The identity of each photoreceptor cell within the epithelium is determined by cell-to-cell contacts involving signal transduction events. The R7 photoreceptor cell requires the activity of the Sevenless RTK to adopt a proper cell fate. We performed an EP screen for negative regulators of this inductive process, and we identified the serine/threonine kinase Center divider (cdi) as a suppressor of the phenotype caused by an activated Sevenless receptor. Cdi is homologous to the human testis-specific kinase 1 (TESK1), a member of the LIM kinases involve...
Genetics, 2014
The Ras/MAPK-signaling pathway plays pivotal roles during development of metazoans by controlling cell proliferation and cell differentiation elicited, in several instances, by receptor tyrosine kinases (RTKs). While the internal mechanism of RTK-driven Ras/ MAPK signaling is well understood, far less is known regarding its interplay with other corequired signaling events involved in developmental decisions. In a genetic screen designed to identify new regulators of RTK/Ras/MAPK signaling during Drosophila eye development, we identified the small GTPase Rap1, PDZ-GEF, and Canoe as components contributing to Ras/MAPK-mediated R7 cell differentiation. Rap1 signaling has recently been found to participate in assembling cadherin-based adherens junctions in various fly epithelial tissues. Here, we show that Rap1 activity is required for the integrity of the apical domains of developing photoreceptor cells and that reduced Rap1 signaling hampers the apical accumulation of the Sevenless RTK in presumptive R7 cells. It thus appears that, in addition to its role in cell-cell adhesion, Rap1 signaling controls the partitioning of the epithelial cell membrane, which in turn influences signaling events that rely on apico-basal cell polarity.
Science, 1987
Tthe determination ofcell fates during the assembly ofthe ommatidia in the compound eye ofDrosopbila appears to be controlled by cell-cell interactions. In this process, the sepenless gene is essential for the development of a single type of photoreceptor cell. In the absence of proper sevenlss function the cells that would normally become the R7 photoreceptors instead become nonneuronal cells. Previous morphological and genetic analysis has indicated that the product of the sevenlss gene is involved in reading or interpreting the positional information that specifies this particular developmental pathway. The sevenless gene has now been isola characterized. The data indicate that sepenkss encodes a transmembrane protein with a tyrosine kinase domain. This structural similarity between sevenless and certain hormone receptors suggests that similar mehanisms are involved in developmental decisions based on cell-cell interaction and physiological or developmental changes induced by diffusible factors.
Neuroscience Research, 1996
Inhibitory signals of cellular differentiation from differentiating cells play an important role in regulating the number and spatial distribution of distinctive types of cells in developing tissues. Several types of inhibitory mechanisms of cellular differentiation have been identified by making full use of the developmental genetics of Drosophila compound eyes. These inhibitory mechanisms are distinct from each other in their signal transduction cascades and/or their role in the pattern formation of the developing Drosophila eye. The following events occur: firstly a diffusible protein, Scabrous (Sca), is required to confer regular spacings of the founder cells, R8 cells, or preommatidial clusters in the developing eye disc via an unknown signal transduction cascade, secondly the Notch-signalling is at least required for the single-out of the R8 cells within the pre-ommatidial cluster possibly by preventing other cells in the equivalent groups from adapting fates as R8 cells. Notch-signalling activates a simple signal cascade mediating communication between the plasma membrane and nucleus not via protein phosphorylation. In contrast, a novel diffusible ligand,.Argos, was likely to be required subsequently to the selection of R8 cells. Argos was shown to inhibit the activation of a receptor tyrosine kinase, DER, and the subsequent signal transduction in the Ras/MAPK cascade (the third inhibitory mechanism). We proposed that the role of Argos is to regulate the number of differentiated cells by controlling cellular differentiation and subsequent programmed cell death. The distinct roles of these inhibitory signals in the developing Drosophila eye are discussed in detail.
The Role of Sevenless in Drosophila R7 Photoreceptor Specification
2019
Sevenless (Sev) is a Receptor Tyrosine Kinase (RTK) that is required for the specification of theDrosophilaR7 photoreceptor. OtherDrosophilaphotoreceptors are specified by the action of another RTK; the Drosophila EGF Receptor (DER). Why Sev is required specifically in the R7 precursor, and the exact role it plays in the cell’s fate assignment have long remained unclear. Notch (N) signaling plays many roles in R7 specification, one of which is to prevent DER activity from establishing the photoreceptor fate. Our current model of Sev function is that it hyperactivates the RTK pathway in the R7 precursor to overcome in the N-imposed block on photoreceptor specification. From this perspective DER and Sev are viewed as engaging the same transduction machinery, the only difference between them being the level of pathway activation that they induce. To test this model, we generated a Sev/DER chimera in which the intracellular domain of Sev is replaced with that of DER. This chimerical rec...