sine oculis(
so) and
eyes absent (
eya) are required for Drosophila eye development and are founding members of the mammalian
Six and
Eya gene families. These genes have been proposed to act with
...eyeless(
Pax6) to regulate eye development in vertebrates and invertebrates.
so encodes a highly diverged homeobox transcription factor and
eya encodes a novel nuclear protein. We demonstrate that So and Eya (1) regulate common steps in eye development including cell proliferation, patterning, and neuronal development; (2) synergize in inducing ectopic eyes; and (3) interact in yeast and in vitro through evolutionarily conserved domains. We propose that an So/Eya complex regulates multiple steps in eye development and functions within the context of a network of genes to specify eye tissue identity.
ABSTRACT
Hippo-Yorkie (Hpo-Yki) signaling is central to diverse developmental processes. Although its redeployment has been amply demonstrated, its context-specific regulation remains poorly ...understood. The Drosophila eye disc is a continuous epithelium folded into two layers, the peripodial epithelium (PE) and the retinal progenitor epithelium. Here, Yki acts in the PE, first to promote PE identity by suppressing retina fate, and subsequently to maintain proper disc morphology. In the latter process, loss of Yki results in the displacement of a portion of the differentiating retinal epithelium onto the PE side. We show that Protein Phosphatase 2A (PP2A) complexes comprising different substrate-specificity B-type subunits govern the Hpo-Yki axis in this context. These include holoenzymes containing the B‴ subunit Cka and those containing the B′ subunits Wdb or Wrd. Whereas PP2A(Cka), as part of the STRIPAK complex, is known to regulate Hpo directly, PP2A(Wdb) acts genetically upstream of the antagonistic activities of the Hpo regulators Sav and Rassf. These in vivo data provide the first evidence of PP2A(B′) heterotrimer function in Hpo pathway regulation and reveal pathway diversification at distinct developmental times in the same tissue.
The specification of organs, tissues and cell types results from cell fate restrictions enacted by nuclear transcription factors under the control of conserved signaling pathways. The progenitor ...epithelium of the
compound eye, the eye imaginal disc, is a premier model for the study of such processes. Early in development, apposing cells of the eye disc are established as either retinal progenitors or support cells of the peripodial epithelium (PE), in a process whose genetic and mechanistic determinants are poorly understood. We have identified protein phosphatase 2A (PP2A), and specifically a STRIPAK-PP2A complex that includes the scaffolding and substrate-specificity components Cka, Strip and SLMAP, as a critical player in the retina-PE fate choice. We show that these factors suppress ectopic retina formation in the presumptive PE and do so via the Hippo signaling axis. STRIPAK-PP2A negatively regulates Hippo kinase, and consequently its substrate Warts, to release the transcriptional co-activator Yorkie into the nucleus. Thus, a modular higher-order PP2A complex refines the activity of this general phosphatase to act in a precise specification of cell fate.
Homeobox transcription factors of the vertebrate CRX/OTX family play critical roles in photoreceptor neurons, the rostral brain and circadian processes. In mouse, the three related proteins, CRX, ...OTX1, and OTX2, fulfill these functions. In Drosophila, the single founding member of this gene family, called orthodenticle (otd), is required during embryonic brain and photoreceptor neuron development. We have used global gene expression analysis in late pupal heads to better characterize the post-embryonic functions of Otd in Drosophila. We have identified 61 genes that are differentially expressed between wild type and a viable eye-specific otd mutant allele. Among them, about one-third represent potentially direct targets of Otd based on their association with evolutionarily conserved Otd-binding sequences. The spectrum of biological functions associated with these gene targets establishes Otd as a critical regulator of photoreceptor morphology and phototransduction, as well as suggests its involvement in circadian processes. Together with the well-documented role of otd in embryonic patterning, this evidence shows that vertebrate and fly genes contribute to analogous biological processes, notwithstanding the significant divergence of the underlying genetic pathways. Our findings underscore the common evolutionary history of photoperception-based functions in vertebrates and invertebrates and support the view that a complex nervous system was already present in the last common ancestor of all bilateria.
The MITF protein is a member of the MYC family of basic helix-loop-helix leucine zipper (bHLH-Zip) transcription factors and is most closely related to the TFE3, TFEC, and TFEB proteins. In the ...mouse, MITF is required for the development of several different cell types, including the retinal pigment epithelial (RPE) cells of the eye. In Mitf mutant mice, the presumptive RPE cells hyperproliferate, abnormally express the retinal transcriptional regulator Pax6, and form an ectopic neural retina. Here we report the structure of the Mitf gene in Drosophila and demonstrate expression during embryonic development and in the eye-antennal imaginal disc. In vitro, transcriptional regulation by Drosophila Mitf, like its mouse counterpart, is modified by the Eyeless (Drosophila Pax6) transcription factor. In vivo, targeted expression of wild-type or dominant-negative Drosophila Mitf results in developmental abnormalities reminiscent of Mitf function in mouse eye development. Our results suggest that the Mitf gene is the original member of the Mitf-Tfe subfamily of bHLH-Zip proteins and that its developmental function is at least partially conserved between vertebrates and invertebrates. These findings further support the common origin of the vertebrate and invertebrate eyes.
The conserved Hippo signalling pathway regulates multiple cellular events, including tissue growth, cell fate decision and neuronal homeostasis. While the core Hippo kinase module appears to mediate ...all the effects of the pathway, various upstream inputs have been identified depending on tissue context. We have recently shown that, in the Drosophila wing imaginal disc, actin-Capping Protein and Hippo pathway activities inhibit F-actin accumulation. In turn, the reduction in F-actin sustains Hpo pathway activity, preventing Yorkie nuclear translocation and the upregulation of proliferation and survival genes. Here, we investigate the role of Capping Protein in growth-unrelated events controlled by the Hippo pathway. We provide evidence that loss of Capping Protein induces degeneration of the adult Drosophila retina through misregulation of the Hippo pathway. We propose a model by which F-actin dynamics might be involved in all processes that require the activity of the core Hippo kinase module.
Abstract Hearing in infants is essential for brain development, acquisition of verbal language skills, and development of social interactions. Therefore, it is important to diagnose hearing loss soon ...after birth so that interventions can be provided as early as possible. Most newborns in the United States are screened for hearing deficits and commercially available next‐generation sequencing hearing loss panels often can identify the causative gene, which may also identify congenital defects in other organs. One of the most prevalent autosomal dominant congenital hearing loss syndromes is branchio‐oto‐renal syndrome (BOR), which also presents with defects in craniofacial structures and the kidney. Currently, mutations in three genes, SIX1, SIX5 , and EYA1 , are known to be causative in about half of the BOR patients that have been tested. To uncover new candidate genes that could be added to congenital hearing loss genetic screens, we have combined the power of Drosophila mutants and protein biochemical assays with the embryological advantages of Xenopus , a key aquatic animal model with a high level of genomic similarity to human, to identify potential Six1 transcriptional targets and interacting proteins that play a role during otic development. We review our transcriptomic, yeast 2‐hybrid, and proteomic approaches that have revealed a large number of new candidates. We also discuss how we have begun to identify how Six1 and co‐factors interact to direct developmental events necessary for normal otic development.
Research Highlights Branchio‐oto‐renal patients have hearing loss and kidney defects. Mutations in SIX1, SIX5 , and EYA1 are causative in about half of cases. To uncover putative new candidate genes, we used Xenopus and identified novel transcriptional targets and interacting proteins.
A host of classical and molecular genetic tools make
Drosophila
a tremendous model for the dissection of gene activity. In particular, the FLP-FRT technique for mitotic recombination has greatly ...enhanced gene loss-of-function analysis. This technique efficiently induces formation of homozygous mutant clones in tissues of heterozygous organisms. However, the dependence of the FLP-FRT method on cell division and other constraints also impose limits on its effectiveness. We describe here the generation and testing of tools for
M
utant
A
nalysis by
R
escue
G
ene
E
xcision (MARGE), an approach whereby mutant cells are formed by loss of a rescue transgene in a homozygous mutant organism. Rescue-transgene loss can be induced in any tissue or cell type and at any time during development or the lifetime of the adult by using available
FLP, Gal4
and
Gal80
ts
reagents. The simultaneous loss of a constitutive fluorescence marker (GFP or RFP) identifies the mutant cells. We demonstrate the efficacy of the MARGE technique by flip-out (clonal and disc-wide) of a
Ubi-GFP
-carrying construct in imaginal discs, and by inducing a known
yki
mutant phenotype in the
Drosophila
ovary.
The v-ATPase is a fundamental eukaryotic enzyme that is central to cellular homeostasis. Although its impact on key metabolic regulators such as TORC1 is well documented, our knowledge of mechanisms ...that regulate v-ATPase activity is limited. Here, we report that the Drosophila transcription factor Mitf is a master regulator of this holoenzyme. Mitf directly controls transcription of all 15 v-ATPase components through M-box cis-sites and this coordinated regulation affects holoenzyme activity in vivo. In addition, through the v-ATPase, Mitf promotes the activity of TORC1, which in turn negatively regulates Mitf. We provide evidence that Mitf, v-ATPase and TORC1 form a negative regulatory loop that maintains each of these important metabolic regulators in relative balance. Interestingly, direct regulation of v-ATPase genes by human MITF also occurs in cells of the melanocytic lineage, showing mechanistic conservation in the regulation of the v-ATPase by MITF family proteins in fly and mammals. Collectively, this evidence points to an ancient module comprising Mitf, v-ATPase and TORC1 that serves as a dynamic modulator of metabolism for cellular homeostasis.
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