Cloning and characterization of two vertebrate homologs of the Drosophila eyes absent gene

All eyes on Eya: A unique transcriptional co-activator and phosphatase in cancer

The Eya family of proteins (consisting of Eyas1-4 in mammals) play vital roles in embryogenesis by regulating processes such as proliferation, migration/invasion, cellular survival and pluripotency/plasticity of epithelial and mesenchymal states. Eya proteins carry out such diverse functions through a unique combination of transcriptional co-factor, Tyr phosphatase, and PP2A/B55α-mediated Ser/Thr phosphatase activities. Since their initial discovery, re-expression of Eyas has been observed in numerous tumor types, where they are known to promote tumor progression through a combination of their transcriptional and enzymatic activities. Eya proteins thus reinstate developmental processes during malignancy and represent a compelling class of therapeutic targets for inhibiting tumor progression.

EYA2 tyrosine phosphatase inhibition reduces MYC and prevents medulloblastoma progression

BACKGROUND

Medulloblastoma is the most common pediatric brain malignancy. Patients with the Group 3 subtype of medulloblastoma (MB) often exhibit MYC amplification and/or overexpression and have the poorest prognosis. While Group 3 MB is known to be highly dependent on MYC, direct targeting of MYC remains elusive.

METHODS

Patient gene expression data were used to identify highly expressed EYA2 in Group 3 MB samples, assess the correlation between EYA2 and MYC, and examine patient survival. Genetic and pharmacological studies were performed on EYA2 in Group 3 derived MB cell models to assess MYC regulation and viability in vitro and in vivo.

RESULTS

EYA2 is more highly expressed in Group 3 MB than other MB subgroups and is essential for Group 3 MB growth in vitro and in vivo. EYA2 regulates MYC expression and protein stability in Group 3 MB, resulting in global alterations of MYC transcription. Inhibition of EYA2 tyrosine phosphatase activity, using a novel small molecule inhibitor (NCGC00249987, or 9987), significantly decreases Group 3 MB MYC expression in both flank and intracranial growth in vivo. Human MB RNA-seq data show that EYA2 and MYC are significantly positively correlated, high EYA2 expression is significantly associated with a MYC transcriptional signature, and patients with high EYA2 and MYC expression have worse prognoses than those that do not express both genes at high levels.

CONCLUSIONS

Our data demonstrate that EYA2 is a critical regulator of MYC in Group 3 MB and suggest a novel therapeutic avenue to target this highly lethal disease.

Eya2 expression during mouse embryonic development revealed by Eya2lacZ knockin reporter and homozygous mice show mild hearing loss

BACKGROUND

Eya2 expression during mouse development has been studied by in situ hybridization and it has been shown to be involved skeletal muscle development and limb formation. Here, we generated Eya2 knockout (Eya2^- ) and a lacZ knockin reporter (Eya2^lacZ ) mice and performed a detailed expression analysis for Eya2^lacZ at different developmental stages to trace Eya2^lacZ -positive cells in Eya2-null mice. We describe that Eya2 is not only expressed in cranial sensory and dorsal root ganglia, retina and olfactory epithelium, and somites as previously reported, but also Eya2 is specifically detected in other organs during mouse development.

RESULTS

We found that Eya2 is expressed in ocular and trochlear motor neurons. In the inner ear, Eya2^lacZ is specifically expressed in differentiating hair cells in both vestibular and cochlear sensory epithelia of the inner ear and Eya2^-/- or Eya2^lacZ/lacZ mice displayed mild hearing loss. Furthermore, we detected Eya2 expression during both salivary gland and thymus development and Eya2-null mice had a smaller thymus.

CONCLUSIONS

As Eya2 is coexpressed with other members of the Eya family genes, these results together highlight that Eya2 as a potential regulator may act synergistically with other Eya genes to regulate the differentiation of the inner ear sensory hair cells and the formation of the salivary gland and thymus.

The Eya1 Phosphatase Mediates Shh-Driven Symmetric Cell Division of Cerebellar Granule Cell Precursors

During neural development, stem and precursor cells can divide either symmetrically or asymmetrically. The transition between symmetric and asymmetric cell divisions is a major determinant of precursor cell expansion and neural differentiation, but the underlying mechanisms that regulate this transition are not well understood. Here, we identify the Sonic hedgehog (Shh) pathway as a critical determinant regulating the mode of division of cerebellar granule cell precursors (GCPs). Using partial gain and loss of function mutations within the Shh pathway, we show that pathway activation determines spindle orientation of GCPs, and that mitotic spindle orientation correlates with the mode of division. Mechanistically, we show that the phosphatase Eya1 is essential for implementing Shh-dependent GCP spindle orientation. We identify atypical protein kinase C (aPKC) as a direct target of Eya1 activity and show that Eya1 dephosphorylates a critical threonine (T410) in the activation loop. Thus, Eya1 inactivates aPKC, resulting in reduced phosphorylation of Numb and other components that regulate the mode of division. This Eya1-dependent cascade is critical in linking spindle orientation, cell cycle exit and terminal differentiation. Together these findings demonstrate that a Shh-Eya1 regulatory axis selectively promotes symmetric cell divisions during cerebellar development by coordinating spindle orientation and cell fate determinants.

Photoperiod-Specific Expression of Eyes Absent 3 Splice Variant in the Pars Tuberalis of the Japanese Quail

The molecular mechanism underlying photoperiodic response in seasonal breeding animals such as the Japanese quail, red jungle fowl, sheep, mouse, and hamster involves thyroid-stimulating hormone beta subunit (TSHβ) mRNA expression in the pars tuberalis stimulated by the extension in day length. Furthermore, this mechanism is regulated by eyes absent 3 (Eya3) in mammals. Even in birds, the expression of both TSHβ and EYA3 is induced in the pars tuberalis by the extension in day length; however, the relationship between the two genes is unknown. To clarify the function of EYA3 in quail photoperiodism, in the present study, we performed mRNA structure analysis of the Japanese quail EYA3 mRNA using reverse transcription-polymerase chain reaction (RT-PCR) and Southern blot analysis. The results revealed that there are four types of splice variants within regions of exons 7, 8, and 9 of quail EYA3 mRNA. Among the four splice variants of quail EYA3, the splice variant containing exon 7 was expressed in the pars tuberalis on the first long day, when quails were transferred from the short-day condition to the long-day condition. The results indicate that EYA3 splice variant containing exon 7 is involved in the photoperiodic response of the pars tuberalis in the Japanese quail.

Eyes absent in the cockroach panoistic ovaries regulates proliferation and differentiation through ecdysone signalling

Eyes absent (Eya), is a protein structurally conserved from hydrozoans to humans, for which two basic roles have been reported: it can act as a transcription cofactor and as a protein tyrosine phosphatase. Eya was discovered in the fly Drosophila melanogaster in relation to its function in eye development, and the same function was later reported in other insects. Eya is also involved in insect oogenesis, although studies in this sense are limited to D. melanogaster, which has meroistic ovaries, and where eya mutations abolish gonad formation. In the present work we studied the function of eya in the panoistic ovary of the cockroach Blattella germanica. We show that eya is essential for correct development of panoistic ovaries. In B. germanica, eya acts at different level and in a distinct way in the germarium and the vitellarium. In the germarium, eya contributes to maintain the correct number of somatic and germinal cells by regulating the expression of steroidogenic genes in the ovary. In the vitellarium, eya facilitates follicle cells proliferation and contributes to regulate the cell program, in the context of basal ovarian follicle maturation. Thus, eya-depleted females of B. germanica arrest the growth and maturation of basal ovarian follicles and become sterile.

Identification of a Small-Molecule Inhibitor That Disrupts the SIX1/EYA2 Complex, EMT, and Metastasis

Metastasis is the major cause of mortality for patients with cancer, and dysregulation of developmental signaling pathways can significantly contribute to the metastatic process. The Sine oculis homeobox homolog 1 (SIX1)/eyes absent (EYA) transcriptional complex plays a critical role in the development of multiple organs and is typically downregulated after development is complete. In breast cancer, aberrant expression of SIX1 has been demonstrated to stimulate metastasis through activation of TGFβ signaling and subsequent induction of epithelial-mesenchymal transition (EMT). In addition, SIX1 can induce metastasis via non-cell autonomous means, including activation of GLI-signaling in neighboring tumor cells and activation of VEGFC-induced lymphangiogenesis. Thus, targeting SIX1 would be expected to inhibit metastasis while conferring limited side effects. However, transcription factors are notoriously difficult to target, and thus novel approaches to inhibit their action must be taken. Here we identified a novel small molecule compound, NCGC00378430 (abbreviated as 8430), that reduces the SIX1/EYA2 interaction. 8430 partially reversed transcriptional and metabolic profiles mediated by SIX1 overexpression and reversed SIX1-induced TGFβ signaling and EMT. 8430 was well tolerated when delivered to mice and significantly suppressed breast cancer-associated metastasis in vivo without significantly altering primary tumor growth. Thus, we have demonstrated for the first time that pharmacologic inhibition of the SIX1/EYA2 complex and associated phenotypes is sufficient to suppress breast cancer metastasis. SIGNIFICANCE: These findings identify and characterize a novel inhibitor of the SIX1/EYA2 complex that reverses EMT phenotypes suppressing breast cancer metastasis.

Eya2 is critical for the E2A‑HLF‑mediated immortalization of mouse hematopoietic stem/progenitor cells

The immunoglobulin enhancer‑binding factor/hepatic leukemia factor (E2A‑HLF) oncogenic fusion gene, generated by t(17;19)(q22;p13) translocation in childhood B‑cell acute lymphoblastic leukemia with a very poor prognosis, encodes a chimeric transcription factor in which the transactivation domains of E2A are fused to the DNA‑binding and dimerization domain of HLF. E2A‑HLF has been demonstrated to have an anti‑apoptotic effect. However, the molecular mechanism underlying E2A‑HLF‑mediated leukemogenesis remains unclear. The present study identified EYA transcriptional coactivator and phosphatase 2 (Eya2), the forced expression of which is known to immortalize mouse hematopoietic stem/progenitor cells (HSPCs), as a direct target molecule downstream of E2A‑HLF. E2A‑HLF‑immortalized mouse HSPCs expressed Eya2 at a high level in the aberrant self‑renewal program. Chromatin immunoprecipitation‑quantitative polymerase chain reaction and a reporter assay revealed that E2A‑HLF enhanced the Eya2 expression by binding to the promoter region containing the E2A‑HLF‑binding consensus sequence. Eya2 knockdown in E2A‑HLF‑immortalized cells resulted in reduced colony‑forming efficiency. These results suggest a critical role of Eya2 in E2A‑HLF‑mediated leukemogenesis.

Mutations that impair Eyes absent tyrosine phosphatase activity in vitro reduce robustness of retinal determination gene network output in Drosophila

A limited collection of signaling networks and transcriptional effectors directs the full spectrum of cellular behaviors that comprise development. One mechanism to diversify regulatory potential is to combine multiple biochemical activities into the same protein. Exemplifying this principle of modularity, Eyes absent (Eya), originally identified as a transcriptional co-activator within the retinal determination gene network (RDGN), also harbors tyrosine and threonine phosphatase activities. Although mounting evidence argues for the importance of Eya’s phosphatase activities to mammalian biology, genetic rescue experiments in Drosophila have shown that the tyrosine phosphatase function is dispensable for normal development. In this study, we repeated these rescue experiments in genetically sensitized backgrounds in which the dose of one or more RDGN factor was reduced. Heterozygosity for sine oculis or dachshund, both core RDGN members, compromised the ability of phosphatase-dead eya, but not of the control wild type eya transgene, to rescue the retinal defects and reduced viability associated with eya loss. We speculate that Eya’s tyrosine phosphatase activity, although non-essential, confers robustness to RDGN output.

Expression pattern of EYA4 in the common marmoset (Callithrix jacchus) cochlea

The eyes absent (EYA)-like genes are essential for the formation of sensory organs among fly (Drosophila melanogaster) and mammals. EYA4, one of the vertebrate genes of Eya family, is reported to be causative for late-onset mid-frequency sensorineural hearing loss in humans, while Eya4-deficient mice exhibited congenital profound deafness and otitis media with effusion due to the eustachian tube dysmorphology. Because of the species difference in the phenotype, the pathophysiology of EYA4 in the human cochlea has yet to be elucidated. Here, we examine the expression pattern of EYA4 in the cochlea of common marmoset (Callithrix jacchus), a non-human primate. The results indicated a distinct expression pattern of EYA4 in the adult marmoset cochleae, especially strong in all supporting cells, while in mouse their expressions were diminished. Interestingly, EYA4 expression in the hair cells, supporting cells and neurons was co-localized with sine oculis homeobox-SIX1, a transcription factor essential for the transcriptional activity of EYA4. The results revealed inter-species differences in the expression pattern of EYA4 gene in supporting cells between primates and rodents. The results also indicated a fundamental role of EYA4 in the primate auditory cells. Experiments with primate models such as marmosets or with human cochlear cells may provide cues about the unknown pathogenesis of EYA4-related hearing loss.

Identification of novel direct targets of Drosophila Sine oculis and Eyes absent by integration of genome-wide data sets

Drosophila eye development is a complex process that involves many transcription factors (TFs) and interactions with their cofactors and targets. The TF Sine oculis (So) and its cofactor Eyes absent (Eya) are highly conserved and are both necessary and sufficient for eye development. Despite their many important roles during development, the direct targets of So are still largely unknown. Therefore the So-dependent regulatory network governing eye determination and differentiation is poorly understood. In this study, we intersected gene expression profiles of so or eya mutant eye tissue prepared from three different developmental stages and identified 1731 differentially expressed genes across the Drosophila genome. A combination of co-expression analyses and motif discovery identified a set of twelve putative direct So targets, including three known and nine novel targets. We also used our previous So ChIP-seq data to assess motif predictions for So and identified a canonical So binding motif. Finally, we performed in vivo enhancer reporter assays to test predicted enhancers from six candidate target genes and find that at least one enhancer from each gene is expressed in the developing eye disc and that their expression patterns overlap with that of So. We furthermore confirmed that the expression level of predicted direct So targets, for which antibodies are available, are reduced in so or eya post-mitotic knockout eye discs. In summary, we expand the set of putative So targets and show for the first time that the combined use of expression profiling of so with its cofactor eya is an effective method to identify novel So targets. Moreover, since So is highly conserved throughout the metazoa, our results provide the basis for future functional studies in a wide variety of organisms.

Multiple Functions of the Eya Phosphotyrosine Phosphatase

Eyes absent (Eya), a protein conserved from plants to humans and best characterized as a transcriptional coactivator, is also the prototype for a novel class of eukaryotic aspartyl protein tyrosine phosphatases. This minireview discusses recent breakthroughs in elucidating the substrates and cellular events regulated by Eya's tyrosine phosphatase function and highlights some of the complexities, new questions, and surprises that have emerged from efforts to understand how Eya's unusual multifunctionality influences developmental regulation and signaling.

Epigenetic silencing of EYA2 in pancreatic adenocarcinomas promotes tumor growth

To identify potentially important genes dysregulated in pancreatic cancer, we analyzed genome-wide transcriptional analysis of pancreatic cancers and normal pancreatic duct samples and identified the transcriptional coactivator, EYA2 (Drosophila Eyes Absent Homologue-2) as silenced in the majority of pancreatic cancers. We investigated the role of epigenetic mechanisms of EYA2 gene silencing in pancreatic cancers, performed in vitro and in vivo proliferation and migration assays to assess the effect of EYA2 silencing on tumor cell growth and metastasis formation, and expression analysis to identify genes transcriptionally regulated by EYA2. We found loss of tumoral Eya2 expression in 63% of pancreatic cancers (120/189 cases). Silencing of EYA2 expression in pancreatic cancer cell lines correlated with promoter methylation and histone deacetylation and was reversible with DNA methyltransferase and HDAC inhibitors. EYA2 knockdown in pancreatic cancer cell lines increased cell proliferation. Compared to parental pancreatic cancer cells, pancreatic cancers stably-expressing EYA2 grew more slowly and had fewer metastases in orthotopic models. The transcriptional changes after stable expression of EYA2 in pancreatic cancer cells included induction of genes in the TGFbeta pathway. Epigenetic silencing of EYA2 is a common event in pancreatic cancers and stable expression EYA2 limits the growth and metastases of pancreatic adenocarcinoma.

Allosteric inhibitors of the Eya2 phosphatase are selective and inhibit Eya2-mediated cell migration

Eya proteins are essential co-activators of the Six family of transcription factors and contain a unique tyrosine phosphatase domain belonging to the haloacid dehalogenase family of phosphatases. The phosphatase activity of Eya is important for the transcription of a subset of Six1-target genes, and also directs cells to the repair rather than apoptosis pathway upon DNA damage. Furthermore, Eya phosphatase activity has been shown to mediate transformation, invasion, migration, and metastasis of breast cancer cells, making it a potential new drug target for breast cancer. We have previously identified a class of N-arylidenebenzohydrazide compounds that specifically inhibit the Eya2 phosphatase. Herein, we demonstrate that these compounds are reversible inhibitors that selectively inhibit the phosphatase activity of Eya2, but not Eya3. Our mutagenesis results suggest that this class of compounds does not bind to the active site and the binding does not require the coordination with Mg(2+). Moreover, these compounds likely bind within a site on the opposite face of the active site, and function as allosteric inhibitors. We also demonstrate that this class of compounds inhibits Eya2 phosphatase-mediated cell migration, setting the foundation for these molecules to be developed into chemical probes for understanding the specific function of the Eya2 phosphatase and to serve as a prototype for the development of Eya2 phosphatase specific anti-cancer drugs.

The EYA-SO/SIX complex in development and disease

Eyes absent (EYA) and Sine oculis (SO/SIX) proteins function as transcriptional activation complexes and play essential roles in organogenesis during embryonic development in regulating cell proliferation and survival and coordination of particular differentiation programs. Mutations of the Eya and So/Six genes cause profound developmental defects in organisms as diverse as flies, frogs, fish, mice, and humans. EYA proteins also possess an intrinsic phosphatase activity, which is essential for normal development. Here, we review crucial roles of EYA and SO/SIX in development and disease in mice and humans.

Eyes absent tyrosine phosphatase activity is not required for Drosophila development or survival

Eyes absent (Eya) is an evolutionarily conserved transcriptional coactivator and protein phosphatase that regulates multiple developmental processes throughout the metazoans. Drosophila eya is necessary for survival as well as for the formation of the adult eye. Eya contains a tyrosine phosphatase domain, and mutations altering presumptive active-site residues lead to strongly reduced activities in ectopic eye induction, in vivo genetic rescue using the Gal4-UAS system, and in vitro phosphatase assays. However, these mutations have not been analyzed during normal development with the correct levels, timing, and patterns of endogenous eya expression. To investigate whether the tyrosine phosphatase activity of Eya plays a role in Drosophila survival or normal eye formation, we generated three eya genomic rescue (eyaGR) constructs that alter key active-site residues and tested them in vivo. In striking contrast to previous studies, all eyaGR constructs fully restore eye formation as well as viability in an eya null mutant background. We conclude that the tyrosine phosphatase activity of Eya is not required for normal eye development or survival in Drosophila. Our study suggests the need for a re-evaluation of the mechanism of Eya action and underscores the importance of studying genes in their native context.

The "eyes absent" (eya) gene in the eye-bearing hydrozoan jellyfish Cladonema radiatum: conservation of the retinal determination network

Eyes absent (Eya) is a member of the Retinal Determination Gene Network (RDGN), a set of genes responsible for eye specification in Drosophila. Eya is a dual function protein, working as a transcription factor in the nucleus and as a tyrosine phosphatase in the cytoplasm. It had been shown that Pax and Six family genes, main components of the RDGN, are present in the hydrozoan Cladonema radiatum and that they are expressed in the eye. However, nothing had been known about the Eya family in hydrozoan jellyfish. Here we report the presence of an Eya homologue (CrEya) in Cladonema. Real-time PCR analysis and in situ hybridization showed that CrEya is expressed in the eye. Furthermore, the comprehensive survey of eukaryote genomes revealed that the acquisition of the N-terminal transactivation domain, including the EYA Domain 2 and its adjacent sequence shared by all eumetazoans, happened early in evolution, before the separation of Cnidaria and Bilateria. Our results uncover the evolution of the two domains and show a conservation of the expression pattern of the Eya gene between Cnidaria and Bilateria, which, together with previous data, supports the hypothesis of the monophyletic origin of metazoans eyes. We additionally show that CrEya is also expressed in the oocytes, where two other members of the RDGN, CrPaxB, and Six4/5-Cr, are known to be expressed. These data suggest that several members of the RDGN have begun to be localized also into the different context of egg development early in the course of metazoan evolution.

EYA1-SIX1 complex in neurosensory cell fate induction in the mammalian inner ear

The phosphatase-transactivator EYA1 interacts with the homeodomain protein SIX1 to form transcriptional activation complexes, which play essential roles in regulating cell proliferation, survival and induction of sensory and neuronal differentiation programs during inner ear development. Mutations of the Eya1 and Six1 genes cause profound developmental auditory defects in mice and humans. The molecular mechanisms and developmental processes controlled by the EYA1 and SIX1 complex in inner ear development and neurosensory fate induction are the focus of this review.

The Eyes Absent proteins in development and disease

The Eyes Absent (EYA) proteins, first described in the context of fly eye development, are now implicated in processes as disparate as organ development, innate immunity, DNA damage repair, photoperiodism, angiogenesis, and cancer metastasis. These functions are associated with an unusual combination of biochemical activities: tyrosine phosphatase and threonine phosphatase activities in separate domains, and transactivation potential when associated with a DNA-binding partner. EYA mutations are linked to multiorgan developmental disorders, as well as to adult diseases ranging from dilated cardiomyopathy to late-onset sensorineural hearing loss. With the growing understanding of EYA biochemical and cellular activity, biological function, and association with disease, comes the possibility that the EYA proteins are amenable to the design of targeted therapeutics. The availability of structural information, direct links to disease states, available animal models, and the fact that they utilize unconventional reaction mechanisms that could allow specificity, suggest that EYAs are well-positioned for drug discovery efforts. This review provides a summary of EYA structure, activity, and function, as they relate to development and disease, with particular emphasis on recent findings.

EWS/FLI1 regulates EYA3 in Ewing sarcoma via modulation of miRNA-708, resulting in increased cell survival and chemoresistance

Ewing sarcoma is an aggressive pediatric cancer of the bone and soft tissue, in which patients whose tumors have a poor histologic response to initial chemotherapy have a poor overall prognosis. Therefore, it is important to identify molecules involved in resistance to chemotherapy. Herein, we show that the DNA repair protein and transcriptional cofactor, EYA3, is highly expressed in Ewing sarcoma tumor samples and cell lines compared with mesenchymal stem cells, the presumed cell-of-origin of Ewing sarcoma, and that it is regulated by the EWS/FLI1 fusion protein transcription factor. We further show that EWS/FLI1 mediates upregulation of EYA3 via repression of miR-708, a miRNA that targets the EYA3 3'-untranslated region, rather than by binding the EYA3 promoter directly. Importantly, we show that high levels of EYA3 significantly correlate with low levels of miR-708 in Ewing sarcoma samples, suggesting that this miR-mediated mechanism of EYA3 regulation holds true in human cancers. Because EYA proteins are important for cell survival during development, we examine, and show, that loss of EYA3 decreases survival of Ewing sarcoma cells. Most importantly, knockdown of EYA3 in Ewing sarcoma cells leads to sensitization to DNA-damaging chemotherapeutics used in the treatment of Ewing sarcoma, and as expected, after chemotherapeutic treatment, EYA3 knockdown cells repair DNA damage less effectively than their control counterparts. These studies identify EYA3 as a novel mediator of chemoresistance in Ewing sarcoma and define the molecular mechanisms of both EYA3 overexpression and of EYA3-mediated chemoresistance.

Interactions with the Abelson tyrosine kinase reveal compartmentalization of eyes absent function between nucleus and cytoplasm

Eyes absent (Eya), named for its role in Drosophila eye development but broadly conserved in metazoa, possesses dual functions as a transcriptional coactivator and protein tyrosine phosphatase. Although Eya's transcriptional activity has been extensively characterized, the physiological requirements for its phosphatase activity remain obscure. In this study, we provide insight into Eya's participation in phosphotyrosine-mediated signaling networks by demonstrating cooperative interactions between Eya and the Abelson (Abl) tyrosine kinase during development of the Drosophila larval visual system. Mechanistically, Abl-mediated phosphorylation recruits Eya to the cytoplasm, where in vivo studies reveal a requirement for its phosphatase function. Thus, we propose a model in which, in addition to its role as a transcription factor, Eya functions as a cytoplasmic protein tyrosine phosphatase.

The eyes absent family of phosphotyrosine phosphatases: properties and roles in developmental regulation of transcription

Integration of multiple signaling pathways at the level of their transcriptional effectors provides an important strategy for fine-tuning gene expression and ensuring a proper program of development. Posttranslational modifications, such as phosphorylation, play important roles in modulating transcription factor activity. The discovery that the transcription factor Eyes absent (Eya) possesses protein phosphatase activity provides an interesting new paradigm. Eya may regulate the phosphorylation state of either itself or its transcriptional cofactors, thereby directly affecting transcriptional output. The identification of a growing number of transcription factors with enzymic activity suggests that such dual-function proteins exert greater control of signaling events than previously imagined. Given the conservation of both its phosphatase and transcription factor activity across mammalian species, Eya provides an excellent model for studying how a single protein integrates these two functions under the influence of multiple signaling pathways to promote development.

Branchio-oto-renal syndrome

Branchio-oto-renal syndrome, a phenotype consisting of hearing loss, auricular malformations, branchial arch remnants, and renal anomalies is now recognized as one of the more common forms of autosomal dominant syndromic hearing impairment. Three loci known to be associated with the BOR phenotype have been identified and two genes that act in a regulatory network have been cloned, EYA1 and SIX1. EYA1 and SIX1 are homologous to genes involved in Drosophila eye development, eyes absent gene (eya), and sine oculis (so), respectively. EYA1, a transcriptional co-activator has a conserved, 271-amino acid, C-terminal known as the Eya Domain (ED). SIX1 has two highly conserved domains; a homeodomain (HD) and a specific Six-domain (SD) whose products function as transcription factors with specific DNA-binding activity that are crucial for protein-protein interaction. To determine the molecular basis for the organ defects that occur in BOR syndrome, many studies have focused on the effects of mutations to EYA and effects of mutations of the EYA-SIX regulatory system. However, over 60% of BOR syndrome patients do not have known mutations in EYA1 and relatively little is known about mutations to SIX1. Further evaluation of SIX1 and its related target genes may provide a better understanding of the pathophysiology of BOR syndrome and offer greater clues to the disease mechanisms.

Identification of transcriptional targets of the dual-function transcription factor/phosphatase eyes absent

Drosophila eye specification and development relies on a collection of transcription factors termed the retinal determination gene network (RDGN). Two members of this network, Eyes absent (EYA) and Sine oculis (SO), form a transcriptional complex in which EYA provides the transactivation function while SO provides the DNA binding activity. EYA also functions as a protein tyrosine phosphatase, raising the question of whether transcriptional output is dependent or independent of phosphatase activity. To explore this, we used microarrays together with binding site analysis, quantitative real-time PCR, chromatin immunoprecipitation, genetics and in vivo expression analysis to identify new EYA-SO targets. In parallel, we examined the expression profiles of tissue expressing phosphatase mutant eya and found that reducing phosphatase activity did not globally impair transcriptional output. Among the targets identified by our analysis was the cell cycle regulatory gene, string (stg), suggesting that EYA and SO may influence cell proliferation through transcriptional regulation of stg. Future investigation into the regulation of stg and other EYA-SO targets identified in this study will help elucidate the transcriptional circuitries whereby output from the RDGN integrates with other signaling inputs to coordinate retinal development.

A novel splice site mutation inEYA4 causes DFNA10 hearing loss

Nonsyndromic autosomal dominant sensorineural hearing loss (SNHL) at the DFNA10 locus was described in two families in 2001. Causative mutations that affect the EyaHR domain of the 'Eyes absent 4' (EYA4) protein were identified. We report on the clinical and genetic analyses of an Australian family with nonsyndromic SNHL. Screening of the EYA4 gene showed the novel polypyrimidine tract variation ca. 1,282-12T > A that introduces a new 3' splice acceptor site. This is the first report of a point mutation in EYA4 that is hypothesized to lead to aberrant pre-mRNA splicing and human disease. The DFNA10 family described is only the fourth to be identified. One individual presented with apparently the same phenotype as other affected members of the family. However, genotyping illustrated that he did not share the DFNA10 disease haplotype. Detailed clinical investigation showed differences in the onset and severity of his hearing loss and thus he is presumed to represent a phenocopy, perhaps resulting from long-term exposure to loud noise.

Xeya3regulates survival and proliferation of neural progenitor cells within the anterior neural plate ofXenopusembryos

The transcriptional coactivater and tyrosine phosphatase eyes absent (eya) is vital for eye development in Drosophila. We identified a vertebrate member of the Eya family, Xeya3, which is expressed in the anterior neural plate, including the eye field. Overexpression of wild-type Xeya3 or of a phosphatase-negative version of Xeya3 creates massive enlargements of brain and retinal tissues, mainly caused by overproliferation of neural precursor cells. On the other hand, suppression of Xeya3 function induces local apoptosis within the sensorial layer of the anterior neuroectoderm. Thus, Xeya3 is key factor for the formation and size control of brain and eyes in vertebrates.

Pax-Six-Eya-Dach network during amphioxus development: conservation in vitro but context specificity in vivo

The Drosophila retinal determination gene network occurs in animals generally as a Pax-Six-Eyes absent-Dachshund network (PSEDN). For amphioxus, we describe the complete network of nine PSEDN genes, four of which-AmphiSix1/2, AmphiSix4/5, AmphSix3/6, and AmphiEya-are characterized here for the first time. For amphioxus, in vitro interactions among the genes and proteins of the network resemble those of other animals, except for the absence of Dach-Eya binding. Amphioxus PSEDN genes are expressed in highly stage- and tissue-specific patterns (sometimes conspicuously correlated with the local intensity of cell proliferation) in the gastrular organizer, notochord, somites, anterior central nervous system, peripheral nervous system, pharyngeal endoderm, and the likely homolog of the vertebrate adenohypophysis. In this last tissue, the anterior region expresses all three amphioxus Six genes and is a zone of active cell proliferation, while the posterior region expresses only AmphiPax6 and is non-proliferative. In summary, the topologies of animal PSEDNs, although considerably more variable than originally proposed, are conserved enough to be recognizable among species and among developing tissues; this conservation may reflect indispensable involvement of PSEDNs during the critically important early phases of embryology (e.g. in the control of mitosis, apoptosis, and cell/tissue motility).

Eya1 regulates the growth of otic epithelium and interacts with Pax2 during the development of all sensory areas in the inner ear

Members of the Eyes absent (Eya) gene family are important for auditory system development. While mutations in human EYA4 cause late-onset deafness at the DFNA10 locus, mutations in human EYA1 cause branchio-oto-renal (BOR) syndrome. Inactivation of Eya1 in mice causes an early arrest of the inner ear development at the otocyst stage. To better understand the role of Eya1 in inner ear development, we analyzed the cellular and molecular basis of the early defect observed in the Eya1 mutant embryos. We report here that Eya1-/- otic epithelium shows reduced cell proliferation from E8.5 and increased cell apoptosis from E9.0, thus providing insights into the cellular basis of inner ear defect which occurred in the absence of Eya1. Previous studies have suggested that Pax, Eya and Six genes function in a parallel or independent pathway during inner ear development. However, it remains unknown whether Pax genes interact with Eya1 or Six1 during inner ear morphogenesis. To further evaluate whether Pax genes function in the Eya1-Six1 pathway or whether they interact with Eya1 or Six1 during inner ear morphogenesis, we have analyzed the expression pattern of Eya1, Pax2 and Pax8 on adjacent sections of otic epithelium from E8.5 to 9.5 by in situ hybridization and the inner ear gross structures of Pax2, Eya1 and Six1 compound mutants at E17.5 by latex paintfilling. Our data strongly suggest that Pax2 interacts with Eya1 during inner ear morphogenesis, and this interaction is critical for the development of all sensory areas in the inner ear. Furthermore, otic marker analysis in both Eya1-/- and Pax2-/- embryos indicates that Eya1 but not Pax2 regulates the establishment of regional specification of the otic vesicle. Together, these results show that, while Eya1 exerts an early function essential for normal growth and patterning of the otic epithelium, it also functionally synergizes with Pax2 during the morphogenesis of all sensory areas of mammalian inner ear.

Induction and specification of cranial placodes

Cranial placodes are specialized regions of the ectoderm, which give rise to various sensory ganglia and contribute to the pituitary gland and sensory organs of the vertebrate head. They include the adenohypophyseal, olfactory, lens, trigeminal, and profundal placodes, a series of epibranchial placodes, an otic placode, and a series of lateral line placodes. After a long period of neglect, recent years have seen a resurgence of interest in placode induction and specification. There is increasing evidence that all placodes despite their different developmental fates originate from a common panplacodal primordium around the neural plate. This common primordium is defined by the expression of transcription factors of the Six1/2, Six4/5, and Eya families, which later continue to be expressed in all placodes and appear to promote generic placodal properties such as proliferation, the capacity for morphogenetic movements, and neuronal differentiation. A large number of other transcription factors are expressed in subdomains of the panplacodal primordium and appear to contribute to the specification of particular subsets of placodes. This review first provides a brief overview of different cranial placodes and then synthesizes evidence for the common origin of all placodes from a panplacodal primordium. The role of various transcription factors for the development of the different placodes is addressed next, and it is discussed how individual placodes may be specified and compartmentalized within the panplacodal primordium. Finally, tissues and signals involved in placode induction are summarized with a special focus on induction of the panplacodal primordium itself (generic placode induction) and its relation to neural induction and neural crest induction. Integrating current data, new models of generic placode induction and of combinatorial placode specification are presented.

Eya1 is required for lineage-specific differentiation, but not for cell survival in the zebrafish adenohypophysis

The homeodomain transcription factor Six1 and its modulator, the protein phosphatase Eya1, cooperate to promote cell differentiation and survival during mouse organ development. Here, we studied the effects caused by loss of eya1 and six1 function on pituitary development in zebrafish. eya1 and six1 are co-expressed in all adenohypophyseal cells. Nevertheless, eya1 (aal, dog) mutants show lineage-specific defects, defining corticotropes, melanotropes, and gonadotropes as an Eya1-dependent lineage, which is complementary to the Pit1 lineage. Furthermore, eya1 is required for maintenance of pit1 expression, leading to subsequent loss of cognate hormone gene expression in thyrotropes and somatotropes of mutant embryos, whereas prolactin expression in lactotropes persists. In contrast to other organs, adenohypophyseal cells of eya1 mutants do not become apoptotic, and the adenohypophysis remains at rather normal size. Also, cells do not trans-differentiate, as in the case of pit1 mutants, but display morphological features characteristic for nonsecretory cells. Some of the adenohypophyseal defects of eya1 mutants are moderately enhanced in combination with antisense-mediated loss of Six1 function, which per se does not affect pituitary cell differentiation. In conclusion, this is the first report of an essential role of Eya1 during pituitary development in vertebrates. Eya1 is required for lineage-specific differentiation of adenohypophyseal cells, but not for their survival, thereby uncoupling the differentiation-promoting and anti-apoptotic effects of Eya proteins seen in other tissues.

Evolutionary origins of vertebrate placodes: insights from developmental studies and from comparisons with other deuterostomes

Ectodermal placodes comprise the adenohypophyseal, olfactory, lens, profundal, trigeminal, otic, lateral line, and epibranchial placodes. The first part of this review presents a brief overview of placode development. Placodes give rise to a variety of cell types and contribute to many sensory organs and ganglia of the vertebrate head. While different placodes differ with respect to location and derivative cell types, all appear to originate from a common panplacodal primordium, induced at the anterior neural plate border by a combination of mesodermal and neural signals and defined by the expression of Six1, Six4, and Eya genes. Evidence from mouse and zebrafish mutants suggests that these genes promote generic placodal properties such as cell proliferation, cell shape changes, and specification of neurons. The common developmental origin of placodes suggests that all placodes may have evolved in several steps from a common precursor. The second part of this review summarizes our current knowledge of placode evolution. Although placodes (like neural crest cells) have been proposed to be evolutionary novelties of vertebrates, recent studies in ascidians and amphioxus have proposed that some placodes originated earlier in the chordate lineage. However, while the origin of several cellular and molecular components of placodes (e.g., regionalized expression domains of transcription factors and some neuronal or neurosecretory cell types) clearly predates the origin of vertebrates, there is presently little evidence that these components are integrated into placodes in protochordates. A scenario is presented according to which all placodes evolved from an adenohypophyseal-olfactory protoplacode, which may have originated in the vertebrate ancestor from the anlage of a rostral neurosecretory organ (surviving as Hatschek's pit in present-day amphioxus).

The C. elegans eyes absent ortholog EYA-1 is required for tissue differentiation and plays partially redundant roles with PAX-6

eyes absent/Eya is a conserved transcriptional coactivator involved in development of various tissues and organs in arthropods and vertebrates. In Drosophila eye development, eya functions as part of the transcriptional regulatory network along with eyeless/Pax6, sine oculis/Six and dachshund/Dach. Here, we present the first functional study of the C. elegans Eya homolog, EYA-1. Loss of EYA-1 function by RNAi and deletion mutations resulted in early larval lethality with incomplete penetrance, associated with defects of differentiation and morphogenesis of several tissues and organs. In late embryogenesis, morphological defect in the head region, pharyngeal malformation and excess cell deaths in the anterior region were observed. Consistently, EYA-1 was expressed in the nuclei of a subset of anterior cells including pharyngeal and body wall muscle cells, starting from the morphogenesis stage in embryogenesis. Interestingly, eya-1 and pax-6/Pax6 mutants showed a strong genetic interaction for larval viability and embryonic anterior morphogenesis. Thus, eya-1 appears to play a partially redundant role with pax-6 during C. elegans embryogenesis.

Using Drosophila to decipher how mutations associated with human branchio-oto-renal syndrome and optical defects compromise the protein tyrosine phosphatase and transcriptional functions of eyes absent

Eyes absent (EYA) proteins are defined by a conserved C-terminal EYA domain (ED) that both contributes to its function as a transcriptional coactivator by mediating protein-protein interactions and possesses intrinsic protein tyrosine phosphatase activity. Mutations in human EYA1 result in an autosomal dominant disorder called branchio-oto-renal (BOR) syndrome as well as congenital cataracts and ocular defects (OD). Both BOR- and OD-associated missense mutations alter residues in the conserved ED as do three missense mutations identified from Drosophila eya alleles. To investigate the molecular mechanisms whereby these mutations disrupt EYA function, we tested their activity in a series of assays that measured in vivo function, phosphatase activity, transcriptional capability, and protein-protein interactions. We find that the OD-associated mutations retain significant in vivo activity whereas those derived from BOR patients show a striking decrease or loss of in vivo functionality. Protein-protein interactions, either with its partner transcription factor Sine oculis or with EYA itself, were not significantly compromised. Finally, the results of the biochemical assays suggest that both loss of protein tyrosine phosphatase activity and reduced transcriptional capability contribute to the impaired EYA function associated with BOR/OD syndrome, thus shedding new light into the molecular mechanisms underlying this disease.

Signaling circuitries in development: insights from the retinal determination gene network

Context-specific integration of information received from the Notch, Transforming growth factor beta, Wingless/Wnt, Hedgehog and Epidermal growth factor receptor signaling pathways sets the stage for deployment of the retinal determination gene network (RDGN), a group of transcription factors that collectively directs the formation of the eye and other tissues. Recent investigations have revealed how these transcription factors are regulated by their interactions with each other and with effectors of the above signaling pathways. Further study of the RDGN may provide insights into how common cues can generate context-specific responses, a key aspect of developmental regulation that remains poorly understood.

Transcriptional Coactivator Drosophila Eyes Absent Homologue 2 Is Up-Regulated in Epithelial Ovarian Cancer and Promotes Tumor Growth

Epithelial ovarian cancer is the most frequent cause of gynecologic malignancy-related mortality in women. To identify genes up-regulated in ovarian cancer, PCR-select cDNA subtraction was done and Drosophila Eyes Absent Homologue 2 (EYA2) was isolated as a promising candidate. The transcriptional coactivator eya controls essential cellular functions during organogenesis of Drosophila. EYA2 mRNA was found to be up-regulated in ovarian cancer by real-time reverse transcription–PCR, whereas its protein product was detected in 93.6% of ovarian cancer specimens by immunohistochemistry (n = 140). EYA2 was amplified in 14.8% of ovarian carcinomas, as detected by array-based comparative genomic hybridization (n = 88). Most importantly, EYA2 overexpression was significantly associated with short overall survival in advanced ovarian cancer (n = 99, P = 0.0361). EYA2 was found to function as transcriptional activator in ovarian cancer cells by Gal4 assay and to promote tumor growth in vivo in xenograft models. Therefore, this study suggests an important role of EYA2 in ovarian cancer and its potential application as a therapeutic target.

A comparative study of Eya1 and Eya4 protein function and its implication in branchio-oto-renal syndrome and DFNA10

Allele variants of EYA1 and EYA4, two members of the vertebrate Eya gene family, underlie two types of inherited human deafness, branchio-oto-renal (BOR) syndrome and DFNA10, respectively. To clarify how mutations in these two genes and their encoded proteins impact the normal biology of hearing, we completed a number of functional studies using the yeast-two-hybrid system. We verified that bait constructs of the homologous region ( Eya1HR and Eya4HR) interact with Six1 prey constructs, although no interaction with Dach1 prey was demonstrable. To compare interaction affinities, we evaluated alpha-galactosidase activity after cotransformation of Eya1HR/Six1 and Eya4HR/Six1 and found that the latter interaction was weaker. By immunofluorescence staining, we showed Eya4HR localization to the cytoplasm. After coexpression of Six1, Eya4HR was translocated to the nucleus. Results with Eya1HR were similar. Translation of mutant constructs ( Eya4HR(R564X) and Eya1HR(R539X)) could not be demonstrated. Using dual Eya-containing constructs (with two wild-type alleles or wild-type and mutant alleles), we confirmed no translation of the mutant allele, even if the mutation was nontruncating. These results are consistent with clinical data and implicate haploinsufficiency as the cause of BOR syndrome and DFNA10.

Functional dissection of eyes absent reveals new modes of regulation within the retinal determination gene network

The retinal determination (RD) gene network encodes a group of transcription factors and cofactors necessary for eye development. Transcriptional and posttranslational regulation of RD family members is achieved through interactions within the network and with extracellular signaling pathways, including epidermal growth factor receptor/RAS/mitogen-activated protein kinase (MAPK), transforming growth factor beta/DPP, Wingless, Hedgehog, and Notch. Here we present the results of structure-function analyses that reveal novel aspects of Eyes absent (EYA) function and regulation. We find that the conserved C-terminal EYA domain negatively regulates EYA transactivation potential, and that GROUCHO-SINE OCULIS (SO) interactions provide another mechanism for negative regulation of EYA-SO target genes. We have mapped the transactivation potential of EYA to an internal proline-, serine-, and threonine-rich region that includes the EYA domain 2 (ED2) and two MAPK phosphorylation consensus sites and demonstrate that activation of the RAS/MAPK pathway potentiates transcriptional output of EYA and the EYA-SO complex in certain contexts. Drosophila S2 cell two-hybrid assays were used to describe a novel homotypic interaction that is mediated by EYA's N terminus. Our data suggest that EYA requires homo- and heterotypic interactions and RAS/MAPK signaling responsiveness to ensure context-appropriate RD gene network activity.

Tissue-specific regulation of retinal and pituitary precursor cell proliferation

Mammalian organogenesis requires the expansion of pluripotent precursor cells before the subsequent determination of specific cell types, but the tissue-specific molecular mechanisms that regulate the initial expansion of primordial cells remain poorly defined. We have genetically established that Six6 homeodomain factor, acting as a strong tissue-specific repressor, regulates early progenitor cell proliferation during mammalian retinogenesis and pituitary development. Six6, in association with Dach corepressors, regulates proliferation by directly repressing cyclin-dependent kinase inhibitors, including the p27Kip1 promoter. These data reveal a molecular mechanism by which a tissue-specific transcriptional repressor-corepressor complex can provide an organ-specific strategy for physiological expansion of precursor populations.

Eya1is required for the morphogenesis of mammalian thymus, parathyroid and thyroid

Eyes absent (Eya) genes regulate organogenesis in both vertebrates and invertebrates. Mutations in human EYA1 cause congenital Branchio-Oto-Renal (BOR) syndrome, while targeted inactivation of murine Eya1 impairs early developmental processes in multiple organs, including ear, kidney and skeletal system. We have now examined the role of Eya1 during the morphogenesis of organs derived from the pharyngeal region, including thymus, parathyroid and thyroid. The thymus and parathyroid are derived from 3rd pharyngeal pouches and their development is initiated via inductive interactions between neural crest-derived arch mesenchyme, pouch endoderm, and possibly the surface ectoderm of 3rd pharyngeal clefts. Eya1 is expressed in all three cell types during thymus and parathyroid development from E9.5 and the organ primordia for both of these structures failed to form in Eya1–/– embryos. These results indicate that Eya1 is required for the initiation of thymus and parathyroid gland formation. Eya1 is also expressed in the 4th pharyngeal region and ultimobranchial bodies. Eya1–/– mice show thyroid hypoplasia, with severe reduction in the number of parafollicular cells and the size of the thyroid lobes and lack of fusion between the ultimobranchial bodies and the thyroid lobe. These data indicate that Eya1 also regulates mature thyroid gland formation. Furthermore, we show that Six1 expression is markedly reduced in the arch mesenchyme, pouch endoderm and surface ectoderm in the pharyngeal region of Eya1–/– embryos, indicating that Six1 expression in those structures is Eya1 dependent. In addition, we show that in Eya1–/– embryos, the expression of Gcm2 in the 3rd pouch endoderm is undetectable at E10.5, however, the expression of Hox and Pax genes in the pouch endoderm is preserved at E9.5-10.5. Finally, we found that the surface ectoderm of the 3rd and 4th pharyngeal region show increased cell death at E10.5 in Eya1–/– embryos. Our results indicate that Eya1 controls critical early inductive events involved in the morphogenesis of thymus, parathyroid and thyroid.

A novel Eyes Absent 2 protein is expressed in the human eye

The Drosophila eyes absent (eya) gene has a role in regulating cell death and/or differentiation and is expressed throughout development. We evaluated the transcripts and proteins encoded by one of the human homologues of Drosophila eya coined Eyes Absent 2 (EYA2). Interestingly, EYA2 was expressed in several neuroblastoma cell lines as four distinct transcripts having alternative 5'-ends, whereas only one EYA2 transcript was expressed in the normal human eye. Due to different translation start sites on the four unique transcripts, two isoforms of EYA2 protein (one previously identified and one novel) could be generated in neuroblastoma cells, but the sole EYA2 transcript expressed in the eye can only encode the novel isoform. Immunoblot analyses suggest that EYA2 may also be post-translationally modified. Finally, the alternative EYA2 transcripts have dissimilar numbers of upstream open reading frames in their 5'-untranslated regions. Therefore, in addition to encoding alternative isoforms of EYA2, regulation of EYA2 expression appears to involve both transcriptional and translational components.

Misexpression of the eyes absent family triggers the apoptotic program

Genetic studies in Drosophila and mice have shown that eyes absent (eya) is an important and conserved transcriptional regulator of development. Along with eyeless/Pax6, sine oculis, and dachshund, eya genes function as master regulators in eye development and can induce ectopic eye formation. Furthermore, the loss-of-function mutants of these genes in the fly causes partial or complete loss of the compound eye, and this is associated with inappropriate apoptosis. Conversely, ectopic eyeless expression in the context of eyes absent or sine oculis mutations results in apoptosis, suggesting that the proper ratio of these factors regulates apoptosis. Here we report that enforced expression of fly eya or of one of its mammalian homologs, Eya2, triggers rapid apoptosis in interleukin-3-dependent 32D.3 murine myeloid cells, which express Eya family members but not Pax6. Eya-induced cell death overrides survival factors and has many features typical of apoptosis, including plasma and mitochondrial membrane changes and caspase activation. Eya-induced apoptosis is blocked by Bcl-2 overexpression but not by the broad-spectrum caspase inhibitor z-VAD.fmk, suggesting that mitochondria are a major target in Eya-induced apoptosis. These results support the concept that inappropriate changes in the steady state levels of Eya proteins may trigger programmed cell deaths during development.

Expression of evolutionarily conserved eye specification genes during Drosophila embryogenesis

Eye specification in Drosophila is thought be controlled by a set of seven nuclear factors that includes the Pax6 homolog, Eyeless. This group of genes is conserved throughout evolution and has been repeatedly recruited for eye specification. Several of these genes are expressed within the developing eyes of vertebrates and mutations in several mouse and human orthologs are the underlying causes of retinal disease syndromes. Ectopic expression in Drosophila of any one of these genes is capable of inducing retinal development, while loss-of-function mutations delete the developing eye. These nuclear factors comprise a complex regulatory network and it is thought that their combined activities are required for the formation of the eye. We examined the expression patterns of four eye specification genes, eyeless (ey), sine oculis (so), eyes absent (eya), and dachshund (dac) throughout all time points of embryogenesis and show that only eyeless is expressed within the embryonic eye anlagen. This is consistent with a recently proposed model in which the eye primordium acquires its competence to become retinal tissue over several time points of development. We also compare the expression of Ey with that of a putative antennal specifying gene Distal-less (Dll). The expression patterns described here are quite intriguing and raise the possibility that these genes have even earlier and wide ranging roles in establishing the head and visual field.

Eyes absent mediates cross-talk between retinal determination genes and the receptor tyrosine kinase signaling pathway

Eyes absent (eya) encodes a member of a network of nuclear transcription factors that promotes eye development in both vertebrates and invertebrates. Despite extensive studies, the molecular mechanisms whereby cell-cell signaling pathways coordinate the function of this retinal determination gene network remain unknown. Here, we report that Drosophila Eya function is positively regulated by mitogen-activated protein kinase (MAPK)-mediated phosphorylation and that this regulation extends to developmental contexts independent of eye determination. In vivo genetic analyses, together with in vitro kinase assay results, demonstrate that Eya is a substrate for extracellular signal-regulated kinase, the MAPK acting downstream in the receptor tyrosine kinase (RTK) signaling pathway. Thus, phosphorylation of Eya appears to provide a direct regulatory link between the RTK/Ras/MAPK signaling cascade and the retinal determination gene network.

Characterization of mouse Dach2, a homologue of Drosophila dachshund

The Drosophila genes eyeless, eyes absent, sine oculis and dachshund cooperate as components of a network to control retinal determination. Vertebrate homologues of these genes have been identified and implicated in the control of cell fate. We present the cloning and characterization of mouse Dach2, a homologue of dachshund. In situ hybridization studies demonstrate Dach2 expression in embryonic nervous tissues, sensory organs and limbs. This pattern is similar to mouse Dach1, suggesting a partially redundant role for these genes during development. In addition, we determine that Dach2 expression in the forebrain of Pax6 mutants and dermamyotome of Pax3 mutants is not detectably altered. Finally, genetic mapping experiments place mouse Dach2 on the X chromosome between Xist and Esx1. The identification of human DACH2 sequences at Xq21 suggests a possible role for this gene in Allan-Herndon syndrome, Miles-Carpenter syndrome, X-linked cleft palate and/or Megalocornea.

The alpha subunits of Gz and Gi interact with the eyes absent transcription cofactor Eya2, preventing its interaction with the six class of homeodomain-containing proteins

Yeast two-hybrid techniques were used to identify possible effectors for the heterotrimeric G protein G(z) in human bone marrow cells. Eya2, a human homologue of the Drosophila Eya transcription co-activator, was identified. Eya2 interacts with activated Galpha(z) and at least one other member of the Galpha(i) family, Galpha(i2). Interactions were confirmed in mammalian two-hybrid and glutathione S-transferase fusion protein pull-down assays. Regions of Eya2-mediating interaction were mapped to the C-terminal Eya consensus domain. Eya2 is an intrinsically cytosolic protein that is translocated to the nucleus by members of the Six homeodomain-containing family of proteins. Activated Galpha(z) and Galpha(i2) prevent Eya2 translocation and inhibit Six/Eya2-mediated activation of a reporter gene controlled through the MEF3/TATA promoter. Although G proteins are known to regulate the activity of numerous transcription factors, this regulation is normally achieved indirectly via one or more intermediates. We show here a novel functional regulation of a co-activator directly by G protein subunits.