The Microphthalmia-associated Transcription Factor (MITF) governs numerous cellular and developmental processes. In mice, it promotes specification and differentiation of the retinal pigmented ...epithelium (RPE), and in humans, some mutations in MITF induce congenital eye malformations. Herein, we explore the function and regulation of Mitf in Drosophila eye development and uncover two roles. We find that knockdown of Mitf results in retinal displacement (RDis), a phenotype associated with abnormal eye formation. Mitf functions in the peripodial epithelium (PE), a retinal support tissue akin to the RPE, to suppress RDis, via the Hippo pathway effector Yorkie (Yki). Yki physically interacts with Mitf and can modify its transcriptional activity in vitro. Severe loss of Mitf, instead, results in the de-repression of retinogenesis in the PE, precluding its development. This activity of Mitf requires the protein phosphatase 2 A holoenzyme STRIPAK-PP2A, but not Yki; Mitf transcriptional activity is potentiated by STRIPAK-PP2A in vitro and in vivo. Knockdown of STRIPAK-PP2A results in cytoplasmic retention of Mitf in vivo and in its decreased stability in vitro, highlighting two potential mechanisms for the control of Mitf function by STRIPAK-PP2A. Thus, Mitf functions in a context-dependent manner as a key determinant of form and fate in the Drosophila eye progenitor epithelium.
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•Mitf works with Yki to preserve eye disc epithelium morphology during eye morphogenesis.•Mitf is a selector factor that promotes peripodial (PE) fate over retinal fate.•Ectopic expression of Mitf blocks retinogenesis.•Mitf works with STRIPAK-PP2A but not Yki in PE development and retina suppression.
Drosophila has three types of visual organs, the larval eyes or Bolwig's organs (BO), the ocelli (OC) and the compound eyes (CE). In all, the bHLH protein Atonal (Ato) functions as the proneural ...factor for photoreceptors and effects the transition from progenitor cells to differentiating neurons. In this work, we investigate the regulation of ato expression in the BO primordium (BOP). Surprisingly, we find that ato transcription in the BOP is entirely independent of the shared regulatory DNA for the developing CE and OC. The core enhancer for BOP expression, atoBO, lies ~6kb upstream of the ato gene, in contrast to the downstream location of CE and OC regulatory elements. Moreover, maintenance of ato expression in the neuronal precursors through autoregulation—a common and ancient feature of ato expression that is well-documented in eyes, ocelli and chordotonal organs—does not occur in the BO. We also show that the atoBO enhancer contains two binding sites for the transcription factor Sine oculis (So), a core component of the progenitor specification network in all three visual organs. These binding sites function in vivo and are specifically bound by So in vitro. Taken together, our findings reveal that the control of ato transcription in the evolutionarily derived BO has diverged considerably from ato regulation in the more ancestral compound eyes and ocelli, to the extent of acquiring what appears to be a distinct and evolutionarily novel cis-regulatory module.
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•Control of ato induction in BO is separate from compound eye or ocellar regulation.•Unlike in other Ato-dependent organs, all BO control lies 5’ to transcription unit.•Cis-sites for retinal determination factor Sine oculis mediate onset of ato in BO.•Unlike in adult eyes and ocelli, ato does not autoregulate in BO founder neurons.•atoBO is an apparently novel CRM for ato transcriptional regulation in the Bolwig’s.
Limb development membrane protein-1 (LMBR1)/lipocalin-interacting membrane receptor (LIMR)-type proteins are putative nine-transmembrane receptors that are evolutionarily conserved across metazoans. ...However, their biological function is unknown. Here, we show that the fly family member Lilipod (Lili) is required for germline stem cell (GSC) self-renewal in theDrosophilaovary where it enhances bone morphogenetic protein (BMP) signaling.lilimutant GSCs are lost through differentiation, and display reduced levels of the Dpp transducer pMad and precocious activation of the master differentiation factorbam.Conversely, overexpressed Lili induces supernumerary pMad-positivebamP-GFP–negative GSCs. Interestingly, differentiation oflilimutant GSCs isbam-dependent; however, its effect on pMad is not. Thus, although it promotes stem cell self-renewal by repressing abam-dependent process, Lilipod enhances transduction of the Dpp signal independently of its suppression of differentiation. In addition, because Lili is still required by a ligand-independent BMP receptor, its function likely occurs between receptor activation and pMad phosphorylation within the signaling cascade. This first, to our knowledge, in vivo characterization of a LMBR1/LIMR-type protein in a genetic model reveals an important role in modulating BMP signaling during the asymmetric division of an adult stem cell population and in other BMP signaling contexts.
During animal development, accurate control of tissue specification and growth are critical to generate organisms of reproducible shape and size. The eye-antennal disc epithelium of Drosophila is a ...powerful model system to identify the signaling pathway and transcription factors that mediate and coordinate these processes. We show here that the Yorkie (Yki) pathway plays a major role in tissue specification within the developing fly eye disc epithelium at a time when organ primordia and regional identity domains are specified. RNAi-mediated inactivation of Yki, or its partner Scalloped (Sd), or increased activity of the upstream negative regulators of Yki cause a dramatic reorganization of the eye disc fate map leading to specification of the entire disc epithelium into retina. On the contrary, constitutive expression of Yki suppresses eye formation in a Sd-dependent fashion. We also show that knockdown of the transcription factor Homothorax (Hth), known to partner Yki in some developmental contexts, also induces an ectopic retina domain, that Yki and Scalloped regulate Hth expression, and that the gain-of-function activity of Yki is partially dependent on Hth. Our results support a critical role for Yki- and its partners Sd and Hth--in shaping the fate map of the eye epithelium independently of its universal role as a regulator of proliferation and survival.
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Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
The Drosophila eye develops from the larval eye disc, a flattened vesicle comprised of continuous retinal and peripodial epithelia (PE). The PE is an epithelium that plays a supporting role in ...retinal neurogenesis, but gives rise to cuticle in the adult. We report here that the PE is also necessary to preserve the morphology of the retinal epithelium. Depletion of the adherens junction (AJ) components β-Catenin (β-Cat), DE-Cadherin or α-Catenin from the PE leads to altered disc morphology, characterized by retinal displacement (RDis); so too does loss of the Ajuba protein Jub, an AJ-associated regulator of the transcriptional coactivator Yorkie (Yki). Restoring AJs or overexpressing Yki in β-Cat deficient PE results in suppression of RDis. Additional suppressors of AJ-dependent RDis include knockdown of Rho kinase (Rok) and Dystrophin (Dys). Furthermore, knockdown of βPS integrin (Mys) from the PE results in RDis, while overexpression of Mys can suppress RDis induced by the loss of β-Cat. We thus propose that AJ-Jub-Yki signaling in PE cells regulates PE cell contractile properties and/or attachment to the extracellular matrix to promote normal eye disc morphology.
Cranial placodes, which give rise to sensory organs in the vertebrate head, are important embryonic structures whose development has not been well studied because of their transient nature and ...paucity of molecular markers. We have used markers of pre-placodal ectoderm (PPE) ( six1, eya1 ) to determine that gradients of both neural inducers and anteroposterior signals are necessary to induce and appropriately position the PPE. Overexpression of six1 expands the PPE at the expense of neural crest and epidermis, whereas knock-down of Six1 results in reduction of the PPE domain and expansion of the neural plate, neural crest and epidermis. Using expression of activator and repressor constructs of six1 or co-expression of wild-type six1 with activating or repressing co-factors ( eya1 and groucho , respectively), we demonstrate that Six1 inhibits neural crest and epidermal genes via transcriptional repression and enhances PPE genes via transcriptional activation. Ectopic expression of neural plate, neural crest and epidermal genes in the PPE demonstrates that these factors mutually influence each other to establish the appropriate boundaries between these ectodermal domains.
During eye development, the selector factors of the Eyeless/Pax6 or Retinal Determination (RD) network control specification of organ-type whereas the bHLH-type proneural factor Atonal drives ...neurogenesis. Although significant progress has been made in dissecting the acquisition of `eye identity' at the transcriptional level, the molecular mechanisms underlying the progression from neuronal progenitor to differentiating neuron remain unclear. A recently proposed model for the integration of organ specification and neurogenesis hypothesizes that atonal expression in the eye is RD-network-independent and that Eyeless works in parallel or downstream of atonal to modify the neurogenetic program. We show here that distinct cis-regulatory elements control atonal expression specifically in the eye and that the RD factors Eyeless and Sine oculis function as direct regulators. We find that these transcription factors interact in vitro and provide indirect evidence that this interaction may be required in vivo. The subordination of neurogenesis to the RD pathway in the eye provides a direct mechanism for the coordination of neurogenesis and tissue specification during sensory organ formation.
The Drosophila decapentaplegic (dpp) gene, encoding a secreted protein of the transforming growth factor-beta (TGF-beta) superfamily, controls proliferation and patterning in diverse tissues, ...including the eye imaginal disc. Pattern formation in this tissue is initiated at the posterior edge and moves anteriorly as a wave; the front of this wave is called the morphogenetic furrow (MF). Dpp is required for proliferation and initiation of pattern formation at the posterior edge of the eye disc. It has also been suggested that Dpp is the principal mediator of Hedgehog function in driving progression of the MF across the disc. In this paper, ectopic Dpp expression is shown to be sufficient to induce a duplicated eye disc with normal shape, MF progression, neuronal cluster formation and direction of axon outgrowth. Induction of ectopic eye development occurs preferentially along the anterior margin of the eye disc. Ectopic Dpp clones situated away from the margins induce neither proliferation nor patterning. The Dpp signalling pathway is shown to be under tight transcriptional and post-transcriptional control within different spatial domains in the developing eye disc. In addition, Dpp positively controls its own expression and suppresses wingless transcription. In contrast to the wing disc, Dpp does not appear to be the principal mediator of Hedgehog function in the eye.
The Decapentaplegic and Notch signaling pathways are thought to direct regional specification in the
Drosophila eye-antennal epithelium by controlling the expression of selector genes for the eye ...(Eyeless/Pax6, Eyes absent) and/or antenna (Distal-less). Here, we investigate the function of these signaling pathways in this process. We find that organ primordia formation is indeed controlled at the level of Decapentaplegic expression but critical steps in regional specification occur earlier than previously proposed. Contrary to previous findings, Notch does not specify eye field identity by promoting Eyeless expression but it influences eye primordium formation through its control of proliferation. Our analysis of Notch function reveals an important connection between proliferation, field size, and regional specification. We propose that field size modulates the interaction between the Decapentaplegic and Wingless pathways, thereby linking proliferation and patterning in eye primordium development.
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