Isolation and characterization of posteriorly restricted genes in the zebrafish gastrula

TALE transcription factors: Cofactors no more

Exd/PBX, Hth/MEIS and PREP proteins belong to the TALE (three-amino-acid loop extension) superclass of transcription factors (TFs) with an atypical homedomain (HD). Originally discovered as "cofactors" to HOX proteins, revisiting their traditional role in light of genome-wide experiments reveals a strong and reproducible pattern of HOX and TALE co-occupancy across diverse embryonic tissues. While confirming that TALE increases HOX specificity and selectivity in vivo, this wider outlook also reveals novel aspects of HOX:TALE collaboration, namely that HOX TFs generally require pre-bound TALE factors to access their functional binding sites in vivo. In contrast to the restricted expression domains of HOX TFs, TALE factors are largely ubiquitous, and PBX and PREP are expressed at the earliest developmental stages. PBX and MEIS control development of many organs and tissues and their dysregulation is associated with congenital disease and cancer. Accordingly, many instances of TALE cooperation with non HOX TFs have been documented in various systems. The model that emerges from these studies is that TALE TFs create a permissive chromatin platform that is selected by tissue-restricted TFs for binding. In turn, HOX and other tissue-restricted TFs selectively convert a ubiquitous pool of low affinity TALE binding events into high confidence, tissue-restricted binding events associated with transcriptional activation. As a result, TALE:TF complexes are associated with active chromatin and domain/lineage-specific gene activity. TALE ubiquitous expression and broad genomic occupancy, as well as the increasing examples of TALE tissue-specific partners, reveal a universal and obligatory role for TALE in the control of tissue and lineage-specific transcriptional programs, beyond their initial discovery as HOX co-factors.

Insights into the pleiotropic roles of ZNF703 in cancer

Zinc finger proteins (ZNFs) belong to the NET/NLZ protein family. In physiological functions, ZNF703 play significant roles in embryonic development, especially in the nervous system. As an transcription factors with zinc finger domains, abnormal regulation of the ZNF703 protein is associated with enhanced proliferation, invasion, and metastasis as well as drug resistance in many tumors, although mechanisms of action vary depending on the specific tumor microenvironment. ZNF703 lacks a nuclear localization sequence despite its function requiring nuclear DNA binding. The purpose of this review is to summarize the architecture of ZNF703, its roles in tumorigenesis, and tumor progression, as well as future oncology therapeutic prospects, which have implications for understanding tumor susceptibility and progression.

ZNF703 promotes tumor progression in ovarian cancer by interacting with HE4 and epigenetically regulating PEA15

Background

It is known that the transcription factor zinc finger protein 703 (ZNF703) plays an important role in physiological functions and the occurrence and development of various tumors. However, the role and mechanism of ZNF703 in ovarian cancer are unclear.

Materials and methods

Immunohistochemistry was used to analyze the expression of ZNF703 in ovarian cancer patients and to assess the effect of ZNF703 expression on the survival and prognosis of ovarian cancer patients. ZNF703 overexpression and suppression expression experiments were used to evaluate the effect of ZNF703 on malignant biological behavior of ovarian cancer cells in vitro. Detecting the interaction between HE4 and ZNF703 by immunofluorescence colocalization and coprecipitation, and nuclear translocation. Chromatin immunoprecipitation-sequencing (ChIP-Seq), dual luciferase reporter assay, ChIP-PCR, in vivo model were applied to study the molecular mechanism of ZNF703 affecting the development of ovarian cancer.

Results

ZNF703 was highly expressed in ovarian cancer tissues, and its expression level is related to the prognosis of ovarian cancer patients. In vivo and in vitro experiments confirmed that ZNF703 overexpression/inhibition expression will promoted/inhibited the malignant biological behavior of ovarian cancer. Mechanically, ZNF703 interacted with HE4, and HE4 promoted nuclear translocation of ZNF703. ChIP-Seq identified multiple regulatory targets of ZNF703, of which ZNF703 directly binds to the enhancer region of PEA15 to promote the transcription of PEA15 and thereby promoted the proliferation of cancer cells.

Conclusion

The results showed that ZNF703 as an oncogene played an important role in the epigenetic modification of ovarian cancer proliferation, and suggested that ZNF703 as a transcription factor may become a prognostic factor and a potential therapeutic target for ovarian cancer.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13046-020-01770-0.

Cisplatin-induced hair cell loss in zebrafish neuromasts is accompanied by protein nitration and Lmo4 degradation

Generation of reactive oxygen species, a critical factor in cisplatin-induced ototoxicity, leads to the formation of peroxynitrite, which in turn results in the nitration of susceptible proteins. Previous studies indicated that LMO4, a transcriptional regulator, is the most abundantly nitrated cochlear protein after cisplatin treatment and that LMO4 nitration facilitates ototoxicity in rodents. However, the role of this mechanism in regulating cisplatin-induced hair cell loss in non-mammalian models is unknown. As the mechanosensory hair cells in the neuromasts of zebrafish share many features with mammalian inner ear and is a good model for studying ototoxicity, we hypothesized that cisplatin treatment induces protein nitration and Lmo4 degradation in zebrafish hair cells, thereby facilitating hair cell loss. Immunostaining with anti-parvalbumin revealed a significant decrease in the number of hair cells in the neuromast of cisplatin treated larvae. In addition, cisplatin treatment induced a significant decrease in the expression of Lmo4 protein and a significant increase in nitrotyrosine levels, in the hair cells. The cisplatin-induced changes in Lmo4 and nitrotyrosine levels strongly correlated with hair cell loss, implying a potential link. Furthermore, a significant increase in the expression of activated Caspase-3 in zebrafish hair cells, post cisplatin treatment, suggested that cisplatin-induced decrease in Lmo4 levels is accompanied by apoptosis. These findings suggest that nitrative stress and Lmo4 degradation are important factors in cisplatin-induced hair cell loss in zebrafish neuromasts and that zebrafish could be used as a model to screen the otoprotective efficacy of compounds that inhibit protein nitration.

Znf703 is a novel RA target in the neural plate border

Znf703 is an RAR- and Wnt-inducible transcription factor that exhibits a complex expression pattern in the developing embryo: Znf703 mRNA is found in the early circumblastoporal ring, then later throughout the neural plate and its border, and subsequently in the mid/hindbrain and somites. We show that Znf703 has a different and separable function in early mesoderm versus neural crest and placode development. Independent of its early knockdown phenotype on Gdf3 and Wnt8, Znf703 disrupts patterning of distinct neural crest migratory streams normally delineated by Sox10, Twist, and Foxd3 and inhibits otocyst formation and otic expression of Sox10 and Eya1. Furthermore, Znf703 promotes massive overgrowth of SOX2+ cells, disrupting the SoxB1 balance at the neural plate border. Despite prominent expression in other neural plate border-derived cranial and sensory domains, Znf703 is selectively absent from the otocyst, suggesting that Znf703 must be specifically cleared or down-regulated for proper otic development. We show that mutation of the putative Groucho-repression domain does not ameliorate Znf703 effects on mesoderm, neural crest, and placodes. We instead provide evidence that Znf703 requires the Buttonhead domain for transcriptional repression.

Dynamic expression and regulation by Fgf8 and Pou2 of the zebrafish LIM-only gene, lmo4

We report the expression of zebrafish lmo4 during the first 48 h of development. Like its murine ortholog, lmo4 is expressed in somitic mesoderm, branchial arches, otic vesicles, and limb (pectoral fin) buds. In addition, however, we report zebrafish lmo4 expression in the developing eye, cardiovascular tissue, and the neural plate and telencephalon. We demonstrate that expression in the rostral hindbrain requires acerebellar (ace/fgf8) and spiel ohne grenzen (spg/pou2) activity.

Characterization of human NLZ1/ZNF703 identifies conserved domains essential for proper subcellular localization and transcriptional repression

NET family members have recently emerged as important players in the development of multiple structures, from the trachea of fly larvae to the vertebrate eye and human breast cancers. However, their mechanisms of action are still poorly understood, and we lack a detailed characterization of their functional domains, as well as gene expression patterns-particularly in adult mammals. Here, we present a characterization of human NLZ1/ZNF703 (NocA-like zinc finger 1/Zinc finger 703), one of the two human NET family member genes. We show that the gene is ubiquitously expressed in adult human and mouse tissues, that three mRNA species with the same coding sequence are generated by alternative polyadenylation, and that the encoded protein contains six evolutionarily conserved domains, three of which are specific to NET proteins. Finally, we present functional evidence that these domains are necessary for proper subcellular distribution of and transcription repression by the NLZ1 protein, but not for its interaction with Groucho family co-repressors.

Cell type and tissue specific function of islet genes in zebrafish pancreas development

Isl1 is a LIM homeobox transcription factor showing conserved expression in the developing and mature vertebrate pancreas. So far, functions of pancreatic Isl1 have mainly been studied in the mouse, where Isl1 has independent functions during formation of exocrine and endocrine tissues. Here, we take advantage of a recently described isl1 mutation in zebrafish to address pancreatic isl1 functions in a non-mammalian system. Isl1 in zebrafish, as in mouse, shows transient expression in mesenchyme flanking the pancreatic endoderm, and continuous expression in all endocrine cells. In isl1 mutants, endocrine cells are specified in normal numbers but more than half of these cells fail to establish expression of endocrine hormones. By using a lineage tracking approach that highlights cells leaving cell cycle early in development, we show that isl1 functions are different in first and second wave endocrine cells. In isl1 mutants, early forming first wave cells show virtually no glucagon expression and a reduced number of cells expressing insulin and somatostatin, while in the later born second wave cells somatostatin expressing cells are strongly reduced and insulin and glucagon positive cells form in normal numbers. Isl1 mutant zebrafish also display a smaller exocrine pancreas. We find that isl1 expression in the pancreatic mesenchyme overlaps with that of the related genes isl2a and isl2b and that pancreatic expression of isl-genes is independent of each other. As a combined block of two or three isl1/2 genes results in a dose-dependent reduction of exocrine tissue, our data suggest that all three genes cooperatively contribute to non-cell autonomous exocrine pancreas extension. The normal expression of the pancreas mesenchyme markers meis3, fgf10 and fgf24 in isl1/2 depleted embryos suggests that this activity is independent of isl-gene function in pancreatic mesenchyme formation as was found in mouse. This indicates species-specific differences in the requirement for isl-genes in pancreatic mesenchyme formation. Overall, our data reveal a novel interaction of isl1 and isl2 genes in exocrine pancreas expansion and cell type specific requirements during endocrine cell maturation.

• Overlapping functions of islet1, islet2a and islet2b in exocrine pancreas formation.

•  Islet1/2a/2b are not required for pancreatic mesenchyme formation.

• Islet1 but not islet2a/b is required for endocrine cell maturation.

• Endocrine cell types are differently affected by the loss of islet1.

Keeping two animal systems in one lab - a frog plus fish case study

For two decades, my lab has been studying development using two vertebrate animals, the frog Xenopus and the zebrafish, Danio. This has been both productive and challenging. The initial rationale for the choice was to compare the same process in two species, as a means to find commonalities that may carry through all vertebrates. As time progressed, however, each species has become exploited for its specific attributes, more than for comparative studies. Maintaining two species simultaneously has been challenging, as has the division of research between the two and making sure that lab members know both systems well enough to communicate productively. Other significant issues concern funding for disparate research, figuring out how to make contributions to both fish and frog communities, and being accepted as a member of two communities. I discuss whether this dual allegiance has been a good idea.

Maternal and zygotic aldh1a2 activity is required for pancreas development in zebrafish

We have isolated and characterized a novel zebrafish pancreas mutant. Mutant embryos lack expression of isl1 and sst in the endocrine pancreas, but retain isl1 expression in the CNS. Non-endocrine endodermal gene expression is less affected in the mutant, with varying degrees of residual expression observed for pdx1, carbA, hhex, prox1, sid4, transferrin and ifabp. In addition, mutant embryos display a swollen pericardium and lack fin buds. Genetic mapping revealed a mutation resulting in a glycine to arginine change in the catalytic domain of the aldh1a2 gene, which is required for the production of retinoic acid from vitamin A. Comparison of our mutant (aldh1a2^um22) to neckless (aldh1a2ⁱ²⁶), a previously identified aldh1a2 mutant, revealed similarities in residual endodermal gene expression. In contrast, treatment with DEAB (diethylaminobenzaldehyde), a competitive reversible inhibitor of Aldh enzymes, produces a more severe phenotype with complete loss of endodermal gene expression, indicating that a source of Aldh activity persists in both mutants. We find that mRNA from the aldh1a2^um22 mutant allele is inactive, indicating that it represents a null allele. Instead, the residual Aldh activity is likely due to maternal aldh1a2, since we find that translation-blocking, but not splice-blocking, aldh1a2 morpholinos produce a phenotype similar to DEAB treatment. We conclude that Aldh1a2 is the primary Aldh acting during pancreas development and that maternal Aldh1a2 activity persists in aldh1a2^um22 and aldh1a2ⁱ²⁶ mutant embryos.

G2 acquisition by transcription-independent mechanism at the zebrafish midblastula transition

Following fertilization of many animal embryos, rapid synchronous cleavage divisions give way to longer, asynchronous cell cycles at the midblastula transition (MBT). The cell cycle changes at the MBT, including the addition of gap phases and checkpoint controls, are accompanied by activation of the zygotic genome and the onset of cell motility. Whereas the biochemical changes accompanying the MBT in the vertebrate embryo have been extensively documented, the cellular events are not well understood. We show that cell cycle remodeling during the zebrafish MBT includes the transcription-independent acquisition of a G2 phase that is essential for preventing entry into mitosis before S-phase completion in cycles 11-13. We provide evidence from high-resolution imaging that inhibition of Cdc25a and Cdk1 activity, but not Cdk2 activity, is essential for cell cycle lengthening and asynchrony between cycles 9 and 12. We demonstrate that lengthening is not required for initiation of zygotic transcription. Our results are consistent with findings from Drosophila and Xenopus that indicate the central importance of G2 addition in checkpoint establishment, and point to similar mechanisms governing the MBT in diverse species.

Organ-specific requirements for Hdac1 in liver and pancreas formation

Liver, pancreas and lung originate from the presumptive foregut in temporal and spatial proximity. This requires precisely orchestrated transcriptional activation and repression of organ-specific gene expression within the same cell. Here, we show distinct roles for the chromatin remodelling factor and transcriptional repressor Histone deacetylase 1 (Hdac1) in endodermal organogenesis in zebrafish. Loss of Hdac1 causes defects in timely liver specification and in subsequent differentiation. Mosaic analyses reveal a cell-autonomous requirement for hdac1 within the hepatic endoderm. Our studies further reveal specific functions for Hdac1 in pancreas development. Loss of hdac1 causes the formation of ectopic endocrine clusters anteriorly to the main islet, as well as defects in exocrine pancreas specification and differentiation. In addition, we observe defects in extrahepatopancreatic duct formation and morphogenesis. Finally, loss of hdac1 results in an expansion of the foregut endoderm in the domain from which the liver and pancreas originate. Our genetic studies demonstrate that Hdac1 is crucial for regulating distinct steps in endodermal organogenesis. This suggests a model in which Hdac1 may directly or indirectly restrict foregut fates while promoting hepatic and exocrine pancreatic specification and differentiation, as well as pancreatic endocrine islet morphogenesis. These findings establish zebrafish as a tractable system to investigate chromatin remodelling factor functions in controlling gene expression programmes in vertebrate endodermal organogenesis.

Zebrafish cdc25a is expressed during early development and limiting for post-blastoderm cell cycle progression

Cdc25 phosphatases are required for eukaryotic cell cycle progression. To investigate mechanisms governing spatiotemporal dynamics of cell cycle progression during vertebrate development, we isolated two cdc25 genes from the zebrafish, Danio rerio, cdc25a, and cdc25d. We propose that Zebrafish cdc25a is the zebrafish orthologue of the tetrapod Cdc25A genes, while cdc25d is of indeterminate origin. We show that both genes have proliferation promoting activity, but that only cdc25d can complement a Schizosaccharomyces pombe loss of function cdc25 mutation. We present expression data demonstrating that cdc25d expression is very limited during early development, while cdc25a is widely expressed and consistent with the mitotic activity in previously identified mitotic domains of the post-blastoderm zebrafish embryo. Finally, we show that cdc25a can accelerate the entry of post-blastoderm cells into mitosis, suggesting that levels of cdc25a are rate limiting for cell cycle progression during gastrulation.

Reciprocal endoderm-mesoderm interactions mediated by fgf24 and fgf10 govern pancreas development

In amniotes, the pancreatic mesenchyme plays a crucial role in pancreatic epithelium growth, notably through the secretion of fibroblast growth factors. However, the factors involved in the formation of the pancreatic mesenchyme are still largely unknown. In this study, we characterize, in zebrafish embryos, the pancreatic lateral plate mesoderm, which is located adjacent to the ventral pancreatic bud and is essential for its specification and growth. We firstly show that the endoderm, by expressing the fgf24 gene at early stages, triggers the patterning of the pancreatic lateral plate mesoderm. Based on the expression of isl1, fgf10 and meis genes, this tissue is analogous to the murine pancreatic mesenchyme. Secondly, Fgf10 acts redundantly with Fgf24 in the pancreatic lateral plate mesoderm and they are both required to specify the ventral pancreas. Our results unveil sequential signaling between the endoderm and mesoderm that is critical for the specification and growth of the ventral pancreas, and explain why the zebrafish ventral pancreatic bud generates the whole exocrine tissue.

A zebrafish LMO4 ortholog limits the size of the forebrain and eyes through negative regulation of six3b and rx3

The Six3 and Rx3 homeodomain proteins are essential for the specification and proliferation of forebrain and retinal precursor cells of the vertebrate brain, and the regulatory networks that control their expression are beginning to be elucidated. We identify the zebrafish lmo4b gene as a negative regulator of forebrain growth that acts via restriction of six3 and rx3 expression during early segmentation stages. Loss of lmo4b by morpholino knockdown results in enlargement of the presumptive telencephalon and optic vesicles and an expansion of the post-gastrula expression domains of six3 and rx3. Overexpression of lmo4b by mRNA injection causes complementary phenotypes, including a reduction in the amount of anterior neural tissue, especially in the telencephalic, optic and hypothalamic primordia, and a dosage-sensitive reduction in six3 and rx3 expression. We suggest that lmo4b activity is required at the neural boundary to restrict six3b expression, and later within the neural plate to for attenuation of rx3 expression independently of its effect on six3 transcription. We propose that lmo4b has an essential role in forebrain development as a modulator of six3 and rx3 expression, and thus indirectly influences neural cell fate commitment, cell proliferation and tissue growth in the anterior CNS.

Fish 'n' chips: the use of microarrays for aquatic toxicology

Gene expression analysis is changing the way that we look at toxicity, allowing toxicologists to perform parallel analyses of entire transcriptomes. While this technology is not as advanced in aquatic toxicology as it is for mammalian models, it has shown promise for determining modes of action, identifying biomarkers and developing "signatures" of chemicals that can be used for field and mixture studies. A major hurdle for the use of microarrays in aquatic toxicology is the lack of sequence information for non-model species. Custom arrays based on gene libraries enriched for genes that are expressed in response to specific contaminants have been used with excellent success for some non-model species, suggesting that this approach will work well for ecotoxicology and spurring on the sequencing of cDNA libraries for species of interest. New sequencing technology and development of repositories for gene expression data will accelerate the use of microarrays in aquatic toxicology. Notwithstanding the preliminary successes that have been achieved even with partial cDNA libraries printed on arrays, ecological samples present elevated challenges for this technology due to the high degree of variation of the samples. Furthermore, recent studies that show nonlinear toxic responses for ecological species underscore the necessity of establishing time and dose dependence of effects on gene expression and comparing these results with traditional markers of toxicity. To realize the full potential of microarrays, researchers must do the experiments required to bridge the gap between the 'omics' technologies and traditional toxicology to demonstrate that microarrays have predictive value in ecotoxicology.

TALE-family homeodomain proteins regulate endodermal sonic hedgehog expression and pattern the anterior endoderm

sonic hedgehog (shh) is expressed in anterior endoderm, where it is required to repress pancreas gene expression and to pattern the endoderm, but the pathway controlling endodermal shh expression is unclear. We find that expression of meis3, a TALE class homeodomain gene, coincides with shh expression in the endoderm of zebrafish embryos. Using a dominant negative construct or anti-sense morpholino oligos (MOs) to disrupt meis3 function, we observe ectopic insulin expression in anterior endoderm. This phenotype is also observed when meis3 MOs are targeted to the endoderm, suggesting that meis3 acts within the endoderm to restrict insulin expression. We also find that meis3 is required for endodermal shh expression, indicating that meis3 acts upstream of shh to restrict insulin expression. Loss of pbx4, a TALE gene encoding a Meis cofactor, produces the same phenotype as loss of meis3, consistent with Meis3 acting in a complex with Pbx4 as reported in other systems. Lastly, we observe a progressive anterior displacement of endoderm-derived organs upon disruption of meis3 or pbx4, apparently as a result of underdevelopment of the pharyngeal region. Our data indicate that meis3 and pbx4 regulate shh expression in anterior endoderm, thereby influencing patterning and growth of the foregut.

MEIS homeobox genes in neuroblastoma

The common pediatric tumor neuroblastoma originates from primitive neural crest-derived precursor cells of the peripheral nervous system. Neuroblastoma especially affects very young children, and can already be present at birth. Its early onset and cellular origin predict the involvement of developmental control genes in neuroblastoma etiology. These genes are indispensable for the tight regulation of normal embryonic development but as a consequence cause cancer and congenital diseases upon mutation or aberrant expression. To date however, the connotation of these genes in neuroblastoma pathogenesis is scant. This review recapitulates data on the MEIS homeobox control genes in cancer and focuses on neuroblastoma.

A novel subfamily of zinc finger genes involved in embryonic development

C2H2 zinc finger proteins make up one of the largest protein families in eukaryotic organisms. Recent study in several different systems has identified a set of novel zinc finger proteins that appear to form a distinct subfamily that we have named the NET family. Members of the NET family (Noc, Nlz, Elbow, and Tlp-1) share two protein motifs--a buttonhead box and an Sp motif--with zinc finger proteins from the Sp family. However, the NET family is uniquely characterized by a single atypical C2H2 zinc finger, in contrast to the Sp family that contains three tandem C2H2 fingers. Here, we review current information about the biochemical function and in vivo role for members of this subfamily. In general, NET family proteins are required during embryonic development. They appear to act by regulating transcription, most likely as repressors, although they are unlikely to bind DNA directly. In the future, it will be important to directly test if NET family proteins control transcription of specific target genes, perhaps via interactions with DNA-binding transcription factors, as well as to further explore their function in vivo.

Zebrafishacvr2a andacvr2b exhibit distinct roles in craniofacial development

To examine the roles of activin type II receptor signaling in craniofacial development, full-length zebrafish acvr2a and acvr2b clones were isolated. Although ubiquitously expressed as maternal mRNAs and in early embryogenesis, by 24 hr postfertilization (hpf), acvr2a and acvr2b exhibit restricted expression in neural, hindbrain, and neural crest cells (NCCs). A morpholino-based targeted protein depletion approach was used to reveal discrete functions for each acvr2 gene product. The acvr2a morphants exhibited defects in the development of most cranial NCC-derived cartilage, bone, and pharyngeal tooth structures, whereas acvr2b morphant defects were largely restricted to posterior arch structures and included the absence and/or aberrant migration of posterior NCC streams, defects in NCC-derived posterior arch cartilages, and dysmorphic pharyngeal tooth development. These studies revealed previously uncharacterized roles for acvr2a and acvr2b in hindbrain and NCC patterning, in NCC derived pharyngeal arch cartilage and joint formation, and in tooth development.

Two Frodo/Dapper homologs are expressed in the developing brain and mesoderm of zebrafish

Members of the Wnt family of extracellular proteins play essential roles during many phases of vertebrate embryonic development. The molecular mechanism of their action involves a complex cascade of intracellular signaling events, which remains to be understood completely. Recently, two novel cytoplasmic modulators of Wnt signaling, Frodo and Dapper, were identified in Xenopus. We report isolation of their homologs in zebrafish, and show that these genes, frd1 and frd2, are expressed in restricted domains during embryogenesis. Both genes are expressed during early gastrulation in the future mesendoderm, and continue to be expressed in distinct patterns in the forming neurectoderm and mesoderm. Comparative sequence analysis and similar expression patterns argue that frd1 is the zebrafish ortholog of Frodo and Dapper, whereas frd2 is a more divergent member of the same family. Our data suggest important roles for zebrafish frd1 and frd2 in patterning the neural plate and several mesodermal derivatives.

nlz gene family is required for hindbrain patterning in the zebrafish

This study describes the conserved nlz gene family whose members encode unusual zinc finger proteins. In the zebrafish neurectoderm, both nlz1 and the newly isolated nlz2 are expressed in the presumptive hindbrain and midbrain/hindbrain boundary, where expression of nlz1 is dependent on pax2a. In addition, nlz2 is uniquely expressed more anteriorly, in the presumptive midbrain and diencephalon. Overexpression of Nlz proteins during gastrula stages inhibits hindbrain development. In particular, ectopically expressed Nlz1 inhibits formation of future rhombomeres 2 and 3 (r2, r3), whereas neighboring r1 and r4 are not affected. Conversely, simultaneous reduction of Nlz1 and Nlz2 protein function by expression of antisense morpholino-modified oligomers leads to expansion of future r3 and r5, with associated loss of r4. These data indicate that one function of the nlz gene family is to specify or maintain r4 identity, and to limit r3 and r5 during hindbrain formation.

Paralog group 1 hox genes regulate rhombomere 5/6 expression of vhnf1, a repressor of rostral hindbrain fates, in a meis-dependent manner

The vertebrate hindbrain is segmented into an array of rhombomeres (r), but it remains to be fully understood how segmentation is achieved. Here we report that reducing meis function transforms the caudal hindbrain to an r4-like fate, and we exploit this experimental state to explore how r4 versus r5-r6 segments are set aside. We demonstrate that r4 transformation of the caudal hindbrain is mediated by paralog group 1 (PG1) hox genes and can be repressed by vhnf1, a gene expressed in r5-r6. We further find that vhnf1 expression is regulated by PG1 hox genes in a meis-dependent manner. This implies that PG1 hox genes not only induce r4 fates throughout the caudal hindbrain, but also induce expression of vhnf1, which then represses r4 fates in the future r5-r6. Our results further indicate that r4 transformation of the caudal hindbrain occurs at intermediate levels of meis function, while extensive removal of meis function produces a hindbrain completely devoid of segments, suggesting that different hox-dependent processes may have distinct meis requirements. Notably, reductions in the function of another Hox cofactor, pbx, have not been reported to transform the caudal hindbrain, suggesting that Meis and Pbx proteins may also function differently in their roles as Hox cofactors.

Differential gene expression analysis in fish exposed to endocrine disrupting compounds

This review discusses various methodologies that can be used to understand, at the gene level, the consequences to fish upon exposure to endocrine disrupting compounds (EDCs). Several approaches for measuring expression of gene transcripts are discussed, including directed approaches, such as Northern blotting and quantitative reverse transcriptase polymerase chain reaction (RT-PCR) as well as open-ended approaches, such as differential display RT-PCR, subtractive hybridizations, and gene arrays. Each of these systems has advantages and disadvantages, strengths and weaknesses. Conducting experiments with each of these methods provides important information about the molecular mechanisms that result from exposure to EDCs, information which can be used in risk assessment of polluted sites found in the environment.

Identification of a developmentally regulated striatum-enriched zinc-finger gene, Nolz-1, in the mammalian brain

Neural information processed through the striatum of the basal ganglia is crucial for sensorimotor and psychomotor functions. Genes that are highly expressed in the striatum during development may be involved in neural development and plasticity in the striatum. We report in the present study the identification of a previously uncharacterized mammalian member of the nocA/elB/tlp-1 family, Nolz-1, that is preferentially expressed at high levels in the developing striatum. Nolz-1 mRNA was expressed as soon as striatal anlage began to form at embryonic day 13 in the rat. Nolz-1 mRNA was predominantly expressed in the lateral ganglionic eminence (striatal primordium) and was nearly absent in the adjacent structures of the medial ganglionic eminence and the cerebral cortex. Moreover, Nolz-1 was highly expressed in the subventricular zone of the lateral ganglionic eminence and was colocalized with the early neuronal differentiation markers of TuJ1 and Isl1 and the projection neuron marker of DARPP-32, suggesting that Nolz-1 was expressed in differentiating progenitors of striatal projection neurons. A time course study showed that Nolz-1 mRNA was developmentally regulated, as its expression was down-regulated postnatally with low levels remaining in the ventral striatum at adulthood. As the tagged Nolz-1 protein was localized in the nucleus, Nolz-1 may function as transcriptional regulator. In a model system for neural differentiation, Nolz-1 mRNA was dramatically induced on neural induction of P19 embryonal carcinoma cells by retinoic acid, suggesting that Nolz-1 activation may be involved in neural differentiation. Our study suggests that Nolz-1 is preferentially expressed in differentiating striatal progenitors and may be engaged in the genetic program for controlling striatal development.

An early Fgf signal required for gene expression in the zebrafish hindbrain primordium

We have explored the role of fibroblast growth factor (Fgf) signaling in regulating gene expression in the early zebrafish hindbrain primordium. We demonstrate that a dominant negative Fgf receptor (FgfR) construct disrupts gene expression along the entire rostrocaudal axis of the hindbrain primordium and, using an FgfR antagonist, we find that this Fgf signal is required at early gastrula stages. This effect cannot be mimicked by morpholino antisense oligos to Fgf3, Fgf8 or Fgf24--three Fgf family members known to be secreted from signaling centers at the midbrain-hindbrain boundary (MHB), in rhombomere 4 and in caudal mesoderm at gastrula stages. We propose that an Fgf signal is required in the early gastrula to initiate hindbrain gene expression and that this is distinct from the later roles of Fgfs in patterning the hindbrain during late gastrula/early segmentation stages. We also find that blocking either retinoic acid (RA) or Fgf signaling disrupts hindbrain gene expression at gastrula stages, suggesting that both pathways are essential at this stage. However, both pathways must be blocked simultaneously to disrupt hindbrain gene expression at segmentation stages, indicating that these signaling pathways become redundant at later stages. Furthermore, exogenous application of RA or Fgf alone is sufficient to induce hindbrain genes in gastrula stage tissues, suggesting that the two-signal requirement can be overcome under some conditions. Our results demonstrate an early role for Fgf signaling and reveal a dynamic relationship between the RA and Fgf signaling pathways during hindbrain development.

Isolation of nlz2 and characterization of essential domains in Nlz family proteins

In this study, we first cloned nlz2, a second zebrafish member of the nlz-related zinc-finger gene family. nlz2 was expressed together with nlz1 in a broad posterior domain during gastrula stages as well as at the midbrain-hindbrain boundary and in the hindbrain caudal to rhombomere 4 during segmentation. nlz2 was also expressed in regions distinct from nlz1, notably in the forebrain, midbrain, and trunk. Misexpression of nlz2 in zebrafish embryos disrupted gene expression in the rostral hindbrain, similar to the effect of misexpressing nlz1. We next compared the nlz1 and nlz2 sequences to identify and characterize domains conserved within this family. We found a C-terminal domain required for nuclear localization and two conserved domains (the Sp motif and a putative C(2)H(2) zinc finger) required for nlz1 function. We also demonstrate that Nlz1 self-associated via its C terminus, interacted with Nlz2, and bound to histone deacetylases. Last, we found two forms of Nlz1 generated from alternative translation initiation sites in vivo. These forms have distinct activities, apparently depending on the function of the N-terminal Sp motif. Our data demonstrate that nlz2 functions similarly to nlz1 and define conserved domains essential for nuclear localization, self-association, and corepressor binding in this novel family of zinc-finger genes.

Nlz belongs to a family of zinc-finger-containing repressors and controls segmental gene expression in the zebrafish hindbrain

The zebrafish nlz gene has a rostral expression limit at the presumptive rhombomere (r) 3/r4 boundary during gastrula stages, and its expression progressively expands rostrally to encompass both r3 and r2 by segmentation stages, suggesting a role for nlz in hindbrain development. We find that Nlz is a nuclear protein that associates with the corepressor Groucho, suggesting that Nlz acts to repress transcription. Consistent with a role as a repressor, misexpression of nlz causes a loss of gene expression in the rostral hindbrain, likely due to ectopic nlz acting prematurely in this domain, and this repression is accompanied by a partial expansion in the expression domains of r4-specific genes. To interfere with endogenous nlz function, we generated a form of nlz that lacks the Groucho binding site and demonstrate that this construct has a dominant negative effect. We find that interfering with endogenous Nlz function promotes the expansion of r5 and, to a lesser extent, r3 gene expression into r4, leading to a reduction in the size of r4. We conclude that Nlz is a transcriptional repressor that controls segmental gene expression in the hindbrain. Lastly, we identify additional nlz-related genes, suggesting that Nlz belongs to a family of zinc-finger proteins.

vhnf1 and Fgf signals synergize to specify rhombomere identity in the zebrafish hindbrain

Vertebrate hindbrain segmentation is a highly conserved process but the mechanism of rhombomere determination is not well understood. Recent work in the zebrafish has shown a requirement for fibroblast growth factor (Fgf) signaling and for the transcription factor variant hepatocyte nuclear factor 1 (vhnf1) in specification of rhombomeres 5 and 6 (r5+r6). We show here that vhnf1 functions in two ways to subdivide the zebrafish caudal hindbrain domain (r4-r7) into individual rhombomeres. First, vhnf1 promotes r5+r6 identity through an obligate synergy with Fgf signals to activate valentino and krox20 expression. Second, vhnf1 functions independently of Fgf signals to repress hoxb1a expression. Although vhnf1 is expressed in a broad posterior domain during gastrulation, it promotes the specification of individual rhombomeres. This is achieved in part because vhnf1 gives cellular competence to respond to Fgf signals in a caudal hindbrain-specific manner.

An expression pattern screen for genes involved in the induction of the posterior nervous system of zebrafish

The posterior nervous system, including the hindbrain and the spinal cord, has been shown to be formed by the transformation of neural plate of anterior character by signals derived from non-axial mesoderm. Although secreted factors, such as fibroblast growth factors (FGFs), Wnts, retinoic acid (RA) and Nodal, have been proposed to be the posteriorizing factors, the mechanism how neural tissue of posterior character is induced and subsequently specified along the anteroposterior axis remains elusive. To identify intercellular signaling molecules responsible for posteriorization of the neural plate as well as to find molecules induced intracellularly by the posteriorizing signal in the caudal neural plate, we screened by in situ hybridization for genes specifically expressed in posterior tissues, including the posterior neural plate and non-axial mesoderm when posteriorization of the neural plate takes place. From a subtracted library differentiating anterior versus posterior neural plate, 420 cDNA clones were tested, out of which 76 cDNA fragments showed expression restricted to the posterior tissue. These clones turned out to represent 32 different genes, including one novel secreted factor and one transmembrane protein. Seven genes were induced by non-axial mesodermal implants and bFGF beads, suggesting that these are among the early-response genes of the posteriorizing signal. Thus, our approach employing cDNA subtraction and subsequent expression pattern screening allows us to clone candidate genes involved in a novel signaling pathway contributing to the formation of the posterior nervous system.

A zebrafish unc-45-related gene expressed during muscle development

We report the isolation and expression pattern of zebrafish unc45r, a gene related to Caenorhabditis elegans unc-45. UNC-45 is a muscle-specific protein thought to interact with myosin and promote the assembly of muscle thick filaments during C. elegans development. Zebrafish Unc45r shares sequence features with C. elegans UNC-45, including three tetratricopeptide repeats and a CRO1/She4p homology domain. unc45r is expressed in mesoderm adjacent to the dorsal midline during late gastrula stages and is coexpressed with muscle specific genes in somitic mesoderm during development of trunk skeletal muscle. unc45r is also expressed in cranial skeletal muscle as well as in cardiac and smooth muscle. The isolation of a muscle-specific unc-45 related gene from zebrafish suggests a common mechanism for muscle filament assembly between vertebrates and invertebrates.

Constructing the hindbrain: insights from the zebrafish

The hindbrain is responsible for controlling essential functions such as respiration and heart beat that we literally do not think about most of the time. In addition, cranial nerves projecting from the hindbrain control muscles in the jaw, eye, and face, and receive sensory input from these same areas. In all vertebrates that have been studied, the hindbrain passes through a segmented phase shortly after the neural tube has formed, with a series of seven bulges--the rhombomeres--forming along the anterior-posterior extent of the neural tube. Our current understanding of vertebrate hindbrain development comes from integrating data from several model systems. Work on the chick has helped us to understand the cell biology of the rhombomeres, whereas the power of mouse molecular genetics has allowed investigation of the molecular mechanisms underlying their development. This review focuses on the special insights that the zebrafish system has provided to our understanding of hindbrain development. As we will discuss, work in the zebrafish has elucidated inductive events that specify the presumptive hindbrain domain and has identified genes required for hindbrain segmentation and the specification of segment identities.

Meis family proteins are required for hindbrain development in the zebrafish

Meis homeodomain proteins function as Hox-cofactors by binding Pbx and Hox proteins to form multimeric complexes that control transcription of genes involved in development and differentiation. It is not known what role Meis proteins play in these complexes, nor is it clear which Hox functions require Meis proteins in vivo. We now show that a divergent Meis family member, Prep1, acts as a Hox co-factor in zebrafish. This suggests that all Meis family members have at least one shared function and that this function must be carried out by a conserved domain. We proceed to show that the Meinox domain, an N-terminal conserved domain shown to mediate Pbx binding, is sufficient to provide Meis activity to a Pbx/Hox complex. We find that this activity is separable from Pbx binding and resides within the M1 subdomain. This finding also presents a rational strategy for interfering with Meis activity in vivo. We accomplish this by expressing the Pbx4/Lzr N-terminus, which sequesters Meis proteins in the cytoplasm away from the nuclear transcription complexes. Sequestering Meis proteins in the cytoplasm leads to extensive loss of rhombomere (r) 3- and r4-specific gene expression, as well as defective rhombomere boundary formation in this region. These changes in gene expression correlate with impaired neuronal differentiation in r3 and r4, e.g. the loss of r3-specific nV branchiomotor neurons and r4-specific Mauthner neurons. We conclude that Meis family proteins are essential for the specification of r3 and r4 of the hindbrain.