The compound eye of Drosophila is used as a model for human disease and homology to eyes in other taxa. This book covers the major discoveries on the development of the compound eye of Drosophila melanogaster over the last 25 years. These include aspects of the biological mechanisms of pattern formation in the nervous system, the specification of neuronal cell types, unexpected phylogenetic conservation and many new insights into the function of several signal transduction pathways. All chapters in this book have been written by leading experts in this field who have made significant contributions to our understanding of fly eye development.

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1 Kevin Moses It is now 25 years since the study of the development of the compound eye in Drosophila really began with a classic paper (Ready et al. 1976). In 1864, August Weismann published a monograph on the development of Diptera and included some beautiful drawings of the developing imaginal discs (Weismann 1864). One of these is the first description of the third instar eye disc in which Weismann drew a vertical line separating a posterior domain that included a regular pattern of clustered cells from an anterior domain without such a pattern. Weismann suggested that these clusters were the precursors of the adult ommatidia and that the line marks the anterior edge of the eye. In his first suggestion he was absolutely correct - in his second he was wrong. The vertical line shown was not the anterior edge of the eye, but the anterior edge of a moving wave of patterning and cell type specification that 112 years later (1976) Ready, Hansen and Benzer would name the "morphogenetic furrow". While it is too late to hear from August Weismann, it is a particular pleasure to be able to include a chapter in this Volume from the first author of that 1976 paper: Don Ready! These past 25 years have seen an astonishing explosion in the study of the fly eye (see Fig.

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References.- Retinal Specification and Determination in Drosophila.- 1 Introduction.- 2 Structure and Early Development of the Drosophila Eye.- 3 The Retinal Determination Network.- 3.1 twin of eyeless and eyeless.- 3.2 eyes absent and sine oculis.- 3.3 dachshund.- 4 Retinal Determination Genes: New Members?.- 4.1 teashirt.- 4.2 optix.- 4.3 eyegone.- 4.4 homothorax and extradentscle.- 5 Patterning Genes and Retinal Determination.- 5.1 hedgehog.- 5.2 decapentaplegic.- 5.3 wingless.- 6 Conclusions and Future Directions.- References.- Regulators of the Morphogenetic Furrow.- 1 Introduction.- 2 Notch Activation Defines the Initiation Point.- 3 Hedgehog is Essential for Morphogenetic Furrow Movement.- 4 Decapentaplegic Promotes Morphogenetic Furrow Movement.- 5 Wingless Inhibits Morphogenetic Furrow Movement.- 6 Conclusions.- References.- NOTCH and the Patterning of Ommatidial Founder Cells in the Developing Drosophila Eye.- 1 Introduction.- 2 The Discovery of Ommatidial Founder Cells.- 2.1 Founder Cells for Each Ommatidium.- 2.2 Spacing Patterns, Lateral Inhibition and Notch.- 3 R8 Cell Specification and Patterning.- 3.1 Specification and Differentiation of R8 Precursors.- 3.2 Mechanism of N Signaling During Lateral Inhibition of R8 Precursors.- 3.3 Selection of Particular Cells Within Each Intermediate Group as R8 Precursors.- 4 Intermediate Group Specification and Patterning.- 4.1 Making an Intermediate Group - Proneural Enhancement.- 4.2 Spacing the Intermediate Groups.- 4.3 Role of the EGF Receptor.- 5 Conclusions.- 5.1 Summary of R8 Specification and Patterning.- 5.2 Comparisons with Other Proneural Groups.- References.- The Epidermal Growth Factor Receptor in Drosophila Eye Development.- 1 Introduction.- 2 EGFR Gene Organization, Protein Structure and Mutant Classes.- 3 EGFR Pathway.- 4 Origin and Structure of the Eye.- 5 Eye Specification.- 6 Cell Fate Specification.- 7 Programmed Cell Death.- 8 Concluding Remarks.- References.- Cell Fate Specification in the Drosophila Eye.- 1 Introduction.- 2 Early Events in Cell Fate Specification.- 3 Undifferentiated Cells.- 4 The Precluster.- 4.1 R8 Specification.- 4.2 R2/R5 Specification.- 4.3 R3/R4 Specification.- 5 The Second Wave of Morphogenesis.- 5.1 R1/R6 Specification.- 5.2 R7 Specification.- 5.3 Cone Cell Specification.- 5.4 Pigment Cell Specification.- 6 Generating and Testing Combinatorial Models.- References.- Tissue Polarity in the Retina.- 1 Tissue Polarization in Development.- 1.1 What Is Tissue Polarity?.- 1.2 Why Is the Retina Polarized?.- 2 The Arrangement of the Ommatidia Within the Plane of the Retina.- 2.1 Establishment of Ommatidial Polarity During Development.- 2.2 The Role of the R3 and R4 Photoreceptors in Ommatidial Polarization.- 3 Genetic Control of Retinal Polarization.- 3.1 The "Tissue Polarity" or Planar Polarity Genes.- 3.2 Frizzled and Dishevelled.- 3.3 A Frizzled Mediated Planar Polarity Signaling Pathway Is Emerging.- 3.4 How Is Frizzled Activity Regulated?.- 3.5 Other Primary Polarity Genes Involved in Retinal Polarity.- 4 How Is the Polarity Signal Interpreted Within a Single Ommatidium?.- 5 Ommatidial Rotation.- 6 General Conclusions.- References.- Regulation of Growth and Cell Proliferation During Eye Development.- 1 Introduction.- 2 Growth and Cell Proliferation During Eye Development.- 3 Mechanisms That Regulate Imaginal Disc Growth.- 3.1 Disc Autonomous Mechanisms That Regulate Growth.- 3.2 Non-Autonomous Control of Disc Growth.- 3.3 Signaling Pathways Regulating Imaginal Disc Growth.- 3.3.1 PI-3 Kinase Pathway.- 3.3.2 Myc.- 3.3.3 Ras/MAPK.- 3.3.4 Cyclin D/cdk4.- 3.3.5 Tscl and Tsc2.- 3.3.6 Drosophila "Tumor-Suppressor" Genes.- 3.3.7 Non-Autonomous Regulators of Growth.- 4 Mechanisms That Regulate Growth and Cell Proliferation in the Eye-Imaginal Disc.- 4.1 Cell Proliferation in First and Second Larval Instar Discs.- 4.2 Cell Proliferation in the Anterior Domain of the Third-Instar Discs.- 4.3 Synchronization of Cells in the Morphogenetic Furrow.- 4.4 Regulation of the Second Mitotic Wave.- 4.5 Exit from the Cell Cycle.- 4.6 Post-Mitotic Growth of the Eye.- 5 Connections Between Disc Patterning and Growth.- 5.1 Lessons from the Wing Disc.- 5.2 Patterned Growth in the Eye Disc; Notch and Morphogen Gradients.- 5.3 Growth Control by Other Patterning Factors.- 5.4 Influence of the Peripodial Membrane.- 5.5 Interactions Between Patterning Networks and Growth Pathways.- 6 Concluding Remarks.- References.- Evolution of Color Vision.- 1 The Retinal Mosaic of the Compound Eye.- 1.1 Rhabdomere and Photoreception.- 1.2 Image Formation and Neural Superposition.- 1.3 Ocelli.- 2 Photoreceptors and Visual Pigments.- 2.1 Color Vision.- 2.2 Evolution and Properties of Rhodopsins.- 2.3 Polarized Light Vision.- 3 Spectral Organization of the Fly Retina.- 3.1 Inner Photoreceptors and Color Vision.- 3.2 Yellow and Pale Ommatidia.- 3.3 Regulation of Rhodopsin Expression.- References.- Developmental Regulation Through Protein Stability.- 1 Introduction.- 2 The Ubiquitin/Proteasome Pathway.- 3 Regulation of Ttk88 Protein Stability.- 3.1 Sina and Phyl Regulate Ttk88 Stability.- 3.1.1 Genetic Evidence.- 3.1.2 Biochemical Evidence.- 3.1.3 Involvement of UbcDl.- 3.2 Ebi, an E3, Also Controls Ttk88 Degradation.- 4 Control of Cell Communication by Faf, a Ubp.- 4.1 Faf Prevents the Mystery Cells from Becoming R-Cells.- 4.1.1 Faf Functions Outside R-Cells.- 4.1.2 Faf Indirectly Downregulates Egfr Activity in R-Cells.- 4.2 Faf Activity Antagonizes Ubiquitination and Proteolysis.- 4.3 The Key Substrate of Faf May Be Lqf, Drosophila Epsin.- 4.4 Faf Activity Facilitates Endocytosis.- 4.5 Faf Also Has a Redundant Function in Eye Development.- 4.6 Models for the Faf Pathway.- 5 Future Directions.- References.- Programmed Death in Eye Development.- 1 Introduction.- 2 Downstream Components: Molecules of Death.- 3 Adaptive Apoptosis: DNA Damage.- 4 Upstream Signals: Death Decisions in the Fly Eye.- 5 Morphogenesis of Lattice Patterning: Making a Hexagon.- 6 Retinal D…