Building a Fly Eye
ABSTRACT In the past, vast differences in ocular structure, development, and physiology throughout the animal kingdom led to the widely accepted notion that eyes are polyphyletic, that is, they have independently arisen multiple times during evolution. Despite the dissimilarity between vertebrate and invertebrate eyes, it is becoming increasingly evident that the development of the eye in both groups shares more similarity at the genetic level than was previously assumed, forcing a reexamination of eye evolution. Understanding the molecular underpinnings of cell type specification during Drosophila eye development has been a focus of research for many labs over the past 25 years, and many of these findings are nicely reviewed in Chapters 1 and 4. A somewhat less explored area of research, however, considers how these cells, once specified, develop into functional ocular structures. This review aims to summarize the current knowledge related to the terminal differentiation events of the retina, corneal lens, and pigmented epithelia in the fly eye. In addition, we discuss emerging evidence that the different functional components of the fly eye share developmental pathways and functions with the vertebrate eye.
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- "We then quantified CC, PR, and PPC numbers by immunostaining for the cell-specific markers Cut, Otd, and BarH1, respectively [36-38] (Table 1). We also analyzed the development of different PR cell types in the adult eye based on morphology and opsin expression - the R1 to R6 outer PRs arrange their actin-rich apical surfaces (rhabdomeres) as a trapezoid surrounding the central smaller R7 inner PR rhabdomere at distal sections, and R7 cells specifically express the opsin proteins Rh3 or Rh4 (Figure 3C,D) . R8 cells are uniquely positioned at the proximal region of the retina, and therefore are not visible in distal retina sections. "
ABSTRACT: The concept of an equivalence group, a cluster of cells with equal potential to adopt the same specific fate, has served as a useful paradigm to understand neural cell type specification. In the Drosophila eye, a set of five cells, called the 'R7 equivalence group', generates a single photoreceptor neuron and four lens-secreting epithelial cells. This choice between neuronal versus non-neuronal cell fates rests on differential requirements for, and cross-talk between, Notch/Delta- and Ras/mitogen-activated protein kinase (MAPK)-dependent signaling pathways. However, many questions remain unanswered related to how downstream events of these two signaling pathways mediate distinct cell fate decisions. Here, we demonstrate that two direct downstream targets of Ras and Notch signaling, the transcription factors Prospero and dPax2, are essential regulators of neuronal versus non-neuronal cell fate decisions in the R7 equivalence group. Prospero controls high activated MAPK levels required for neuronal fate, whereas dPax2 represses Delta expression to prevent neuronal fate. Importantly, activity from both factors is required for proper cell fate decisions to occur. These data demonstrate that Ras and Notch signaling are integrated during cell fate decisions within the R7 equivalence group through the combinatorial and opposing activities of Pros and dPax2. Our study provides one of the first examples of how the differential expression and synergistic roles of two independent transcription factors determine cell fate within an equivalence group. Since the integration of Ras and Notch signaling is associated with many developmental and cancer models, these findings should provide new insights into how cell specificity is achieved by ubiquitously used signaling pathways in diverse biological contexts.Neural Development 05/2011; 6(1):20. DOI:10.1186/1749-8104-6-20 · 3.45 Impact Factor
Article: 800 Facets of Retinal Degeneration[Show abstract] [Hide abstract]
ABSTRACT: In today's world of genomics and large computational analyses, rapid progress has been made in identifying genes associated with human retinal diseases. Nevertheless, before significant advances toward effective therapeutic intervention is made, a clearer understanding of the molecular and cellular role of these gene products in normal and diseased photoreceptor cell biology is required. Given the complexity of the vertebrate retina, these advancements are unlikely to be revealed in isolated human cell lines, but instead, will require the use of numerous model systems. Here, we describe several parallels between vertebrate and invertebrate photoreceptor cell biology that are beginning to emerge and advocate the use of Drosophila melanogaster as a powerful genetic model system for uncovering molecular mechanisms of human retinal pathologies, in particular photoreceptor neurodegeneration.Progress in molecular biology and translational science 01/2011; 100:331-68. DOI:10.1016/B978-0-12-384878-9.00008-X · 3.49 Impact Factor
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ABSTRACT: The evolution of the eye has been a major subject of study dating back centuries. The advent of molecular genetics offered the surprising finding that morphologically distinct eyes rely on conserved regulatory gene networks for their formation. While many of these advances often stemmed from studies of the compound eye of the fruit fly, Drosophila melanogaster, and later translated to discoveries in vertebrate systems, studies on vertebrate lens development far outnumber those in Drosophila. This may be largely historical, since Spemann and Mangold's paradigm of tissue induction was discovered in the amphibian lens. Recent studies on lens development in Drosophila have begun to define molecular commonalities with the vertebrate lens. Here, we provide an overview of Drosophila lens development, discussing intrinsic and extrinsic factors controlling lens cell specification and differentiation. We then summarize key morphological and molecular events in vertebrate lens development, emphasizing regulatory factors and networks strongly associated with both systems. Finally, we provide a comparative analysis that highlights areas of research that would help further clarify the degree of conservation between the formation of dioptric systems in invertebrates and vertebrates.MGG Molecular & General Genetics 08/2011; 286(3-4):189-213. DOI:10.1007/s00438-011-0643-y · 2.73 Impact Factor