Involvement of the zebrafish trrap gene in craniofacial development.

Trrap (transformation/transcription domain-associated protein) is a component shared by several histone acetyltransferase (HAT) complexes and participates in transcriptional regulation and DNA repair; however, the developmental functions of Trrap in vertebrates are not fully understood. Recently, it has been reported that human patients with genetic mutations in the TRRAP gene show various symptoms, including facial dysmorphisms, microcephaly and global developmental delay. To investigate the physiological functions of Trrap, we established trrap gene-knockout zebrafish and examined loss-of-function phenotypes in the mutants. The trrap zebrafish mutants exhibited smaller eyes and heads than the wild-type zebrafish. The size of the ventral pharyngeal arches was reduced and the mineralization of teeth was impaired in the trrap mutants. Whole-mount in situ hybridization analysis revealed that dlx3 expression was narrowly restricted in the developing ventral pharyngeal arches, while dlx2b expression was diminished in the trrap mutants. These results suggest that trrap zebrafish mutants are useful model organisms for a human disorder associated with genetic mutations in the human TRRAP gene.

Critical roles of the ddx5 gene in zebrafish sex differentiation and oocyte maturation.

DEAD-box helicase 5 (Ddx5) functions as an ATP-dependent RNA helicase and as a transcriptional coactivator for several transcription factors; however, the developmental function of the ddx5 gene in vertebrates is not fully understood. We found that the zebrafish ddx5 gene was expressed in developing gonads. Using the genome editing technology transcription activator-like effector nuclease, we established a ddx5-disrupted zebrafish and examined the morphological phenotypes of the mutant. We found that the majority of ddx5-deficient mutants developed as fertile males with normal testes and a small number of ddx5-deficient mutants developed as infertile females with small ovaries. Apoptotic cell death at 31 days post fertilization was increased in thick immature gonads (presumptive developing ovaries) of the ddx5-deficient mutant compared to those of heterozygous wild-type fish, while the number of apoptotic cells in thin immature gonads (presumptive developing testes) was comparable between the mutant and wild-type animals. Histological analysis revealed that ovaries of adult ddx5-deficient females had fewer vitellogenic oocytes and a larger number of stage I and II oocytes. The amount of cyclic adenosine monophosphate in the ddx5-deficient ovaries was high compared to that of wild-type ovaries, presumably leading to the mitotic arrest of oocyte maturation. Therefore, the ddx5 gene is dispensable for testis development, but it is essential for female sex differentiation and oocyte maturation in zebrafish.

Characterization of biklf/klf17-deficient zebrafish in posterior lateral line neuromast and hatching gland development.

Krüpple-like factors (Klfs) are highly conserved zinc-finger transcription factors that regulate various developmental processes, such as haematopoiesis and cardiovascular development. In zebrafish, transient knockdown analysis of biklf/klf17 using antisense morpholino suggests the involvement of biklf/klf17 in primitive erythropoiesis and hatching gland development; however, the continuous physiological importance of klf17 remains uncharacterized under the genetic ablation of the klf17 gene among vertebrates. We established the klf17-disrupted zebrafish lines using the CRISPR/Cas9 technology and performed phenotypic analysis throughout early embryogenesis. We found that the klf17-deficient embryos exhibited abnormal lateral line neuromast deposition, whereas the production of primitive erythrocytes and haemoglobin production were observed in the klf17-deficient embryos. The expression of lateral line neuromast genes, klf17 and s100t, in the klf17-deficient embryos was detected in posterior lateral line neuromasts abnormally positioned at short intervals. Furthermore, the klf17-deficient embryos failed to hatch and died without hatching around 15 days post-fertilization (dpf), whereas the dechorionated klf17-deficient embryos and wild-type embryos were alive at 15 dpf. The klf17-deficient embryos abolished hatching gland cells and Ctsl1b protein expression, and eliminated the expression of polster and hatching gland marker genes, he1.1, ctsl1b and cd63. Thus, the klf17 gene plays important roles in posterior lateral line neuromast and hatching gland development.

Involvement of the centrosomal protein 55 (cep55) gene in zebrafish head formation.

Mammalian CEP55 (centrosomal protein 55 kDa) is a coiled-coil protein localized to the centrosome in interphase cells and is required for cytokinesis. A homozygous non-sense mutation in human CEP55 has been recently identified in perinatal lethal MARCH (multinucleated neurons, anhydramnios, renal dysplasia, cerebellar hypoplasia and hydranencephaly) syndrome. We have isolated zebrafish cep55 mutants defective in head morphology. The zebrafish cep55 gene was expressed in the head including the retina and the pectoral fin at 1 day post-fertilization (dpf), and extensive cell death was widely observed in the head and tail of the cep55 mutant. In the cep55 mutant, the anterior-posterior distance of the ventral pharyngeal arches was short, and retinal lamination was disorganized. Neural cells, such as islet1-positive cells and pax2-positive cells, and fli1b-positive vascular cells were reduced in the head of the cep55 mutant. Thus, we propose that the zebrafish cep55 mutant is a model organism for human MARCH syndrome.

Spatiotemporal expression of the cocaine- and amphetamine-regulated transcript-like (cart-like) gene during zebrafish embryogenesis.

The cocaine- and amphetamine-regulated transcript (CART) genes are involved in the neural regulation of energy homeostasis; however, their developmental expressions and functions are not fully understood in vertebrates. We have identified a novel zebrafish cart-like gene that encodes a protein of 105 amino acids possessing sequence similarity to zebrafish and mammalian CART proteins. RT-PCR analysis revealed that the cart-like transcripts were maternally supplied and gradually decreased during the cleavage, blastula and gastrula stages; then, transcripts subsequently reaccumulated at the segmentation, pharyngula and hatching stages. Based on a whole-mount in situ hybridization analysis using an antisense cart-like RNA probe, we found that the cart-like transcript was predominantly expressed in both the Rohon-Beard neurons and trigeminal ganglia, suggesting the involvement of the cart-like gene in zebrafish neural development.

Developmental expression of the slurp-like1/ly2.3/ly97.3 and slurp-like2/ly2.2/ly97.2 genes during zebrafish early embryogenesis.

Mammalian SLURP1 and SLURP2 belong to the Ly-6/uPAR superfamily and are involved in maintaining the physiological integrity of keratinocytes. However, the developmental expression and functions of other Ly-6/uPAR family genes in vertebrates are still obscure. We have isolated novel Ly-6/uPAR family genes slurp-like1 (ly2.3/ly97.3) and slurp-like2 (ly2.2/ly97.2) in zebrafish. Both the Slurp-like1 and Slurp-like2 proteins contain the typical signal sequence and carboxy-terminal CCXXXXCN (X: an arbitrary amino acid) consensus sequence of the Ly-6/uPAR family but lack a transmembrane domain and a GPI-anchoring signal sequence, suggesting that both proteins may function as secretory proteins. Whole-mount in situ hybridization analysis revealed that slurp-like1 was predominantly expressed in the floor plate of the neural tube and in the hypochord of the notochord at 24 h post-fertilization (hpf) and detected in the liver and intestinal bulb at 72 hpf, while slurp-like2 was expressed in the midbrain and hindbrain at 24 hpf and detected in the liver and pancreas at 72 hpf. Differential expression profiles of the slurp-like1 and slurp-like2 genes suggest the distinct physiological involvement of these genes in zebrafish early embryogenesis.

Functional visualization and disruption of targeted genes using CRISPR/Cas9-mediated eGFP reporter integration in zebrafish.

The CRISPR/Cas9 complex, which is composed of a guide RNA (gRNA) and the Cas9 nuclease, is useful for carrying out genome modifications in various organisms. Recently, the CRISPR/Cas9-mediated locus-specific integration of a reporter, which contains the Mbait sequence targeted using Mbait-gRNA, the hsp70 promoter and the eGFP gene, has allowed the visualization of the target gene expression. However, it has not been ascertained whether the reporter integrations at both targeted alleles cause loss-of-function phenotypes in zebrafish. In this study, we have inserted the Mbait-hs-eGFP reporter into the pax2a gene because the disruption of pax2a causes the loss of the midbrain-hindbrain boundary (MHB) in zebrafish. In the heterozygous Tg[pax2a-hs:eGFP] embryos, MHB formed normally and the eGFP expression recapitulated the endogenous pax2a expression, including the MHB. We observed the loss of the MHB in homozygous Tg[pax2a-hs:eGFP] embryos. Furthermore, we succeeded in integrating the Mbait-hs-eGFP reporter into an uncharacterized gene epdr1. The eGFP expression in heterozygous Tg[epdr1-hs:eGFP] embryos overlapped the epdr1 expression, whereas the distribution of eGFP-positive cells was disorganized in the MHB of homozygous Tg[epdr1-hs:eGFP] embryos. We propose that the locus-specific integration of the Mbait-hs-eGFP reporter is a powerful method to investigate both gene expression profiles and loss-of-function phenotypes.

Comprehensive analysis of sphingosine-1-phosphate receptor mutants during zebrafish embryogenesis.

The lipid mediator sphingosine-1-phosphate (S1P) regulates various physiological and pathological phenomena such as angiogenesis and oncogenesis. Secreted S1P associates with the G-protein-coupled S1P receptors (S1PRs), leading to the activation of downstream signaling molecules. In mammals, five S1prs have been identified and the genetic disruption of a single S1pr1 gene causes vascular defects. In zebrafish, seven s1prs have been isolated. We found that individual s1prs showed unique expression patterns with some overlapping expression domains during early embryogenesis. We generated all s1pr single-mutant zebrafish by introducing premature stop codons in their coding regions using transcription activator-like effector nucleases and analyzed their phenotypes during early embryogenesis. Zygotic s1pr1, s1pr3a, s1pr3b, s1pr4, s1pr5a and s1pr5b mutants showed no developmental defects and grew into adults, whereas zygotic s1pr2 mutant showed embryonic lethality with a cardiac defect, showing quite distinct embryonic phenotypes for individual S1pr mutants between zebrafish and mouse. We further generated maternal-zygotic s1pr1, s1pr3a, s1pr3b, s1pr4, s1pr5a and s1pr5b mutants and found that these maternal-zygotic mutants also showed no obvious developmental defects, presumably suggesting the redundant functions of the S1P receptor-mediated signaling in zebrafish.

Efficient Multiple Genome Modifications Induced by the crRNAs, tracrRNA and Cas9 Protein Complex in Zebrafish.

The type II clustered regularly interspaced short palindromic repeats (CRISPR) associated with Cas9 endonuclease (CRISPR/Cas9) has become a powerful genetic tool for understanding the function of a gene of interest. In zebrafish, the injection of Cas9 mRNA and guide-RNA (gRNA), which are prepared using an in vitro transcription system, efficiently induce DNA double-strand breaks (DSBs) at the targeted genomic locus. Because gRNA was originally constructed by fusing two short RNAs CRISPR RNA (crRNA) and trans-activating crRNA (tracrRNA), we examined the effect of synthetic crRNAs and tracrRNA with Cas9 mRNA or Cas9 protein on the genome editing activity. We previously reported that the disruption of tyrosinase (tyr) by tyr-gRNA/Cas9 mRNA causes a retinal pigment defect, whereas the disruption of spns2 by spns2-gRNA1/Cas9 mRNA leads to a cardiac progenitor migration defect in zebrafish. Here, we found that the injection of spns2-crRNA1, tyr-crRNA and tracrRNA with Cas9 mRNA or Cas9 protein simultaneously caused a migration defect in cardiac progenitors and a pigment defect in retinal epithelial cells. A time course analysis demonstrated that the injection of crRNAs and tracrRNA with Cas9 protein rapidly induced genome modifications compared with the injection of crRNAs and tracrRNA with Cas9 mRNA. We further show that the crRNA-tracrRNA-Cas9 protein complex is functional for the visualization of endogenous gene expression; therefore, this is a very powerful, ready-to-use system in zebrafish.

Maternal and Zygotic Sphingosine Kinase 2 Are Indispensable for Cardiac Development in Zebrafish.

Sphingosine 1-phosphate (S1P) is synthesized from sphingosine by sphingosine kinases (SPHK1 and SPHK2) in invertebrates and vertebrates, whereas specific receptors for S1P (S1PRs) selectively appear in vertebrates, suggesting that S1P acquires novel functions in vertebrates. Because the developmental functions of SPHK1 and SPHK2 remain obscure in vertebrates, we generated sphk1 or sphk2 gene-disrupted zebrafish by introducing premature stop codons in their coding regions using transcription activator-like effector nucleases. Both zygotic sphk1 and sphk2 zebrafish mutants exhibited no obvious developmental defects and grew to adults. The maternal-zygotic sphk2 mutant (MZsphk2), but not the maternal-zygotic sphk1 mutant and maternal sphk2 mutant, had a defect in the cardiac progenitor migration and a concomitant decrease in S1P level, leading to a two-heart phenotype (cardia bifida). Cardia bifida in MZsphk2, which was rescued by injecting sphk2 mRNA, was a phenotype identical to that of zygotic mutants of the S1P transporter spns2 and S1P receptor s1pr2, indicating that the Sphk2-Spns2-S1pr2 axis regulates the cardiac progenitor migration in zebrafish. The contribution of maternally supplied lipid mediators during vertebrate organogenesis presents as a requirement for maternal-zygotic Sphk2.

Precise in-frame integration of exogenous DNA mediated by CRISPR/Cas9 system in zebrafish.

The CRISPR/Cas9 system provides a powerful tool for genome editing in various model organisms, including zebrafish. The establishment of targeted gene-disrupted zebrafish (knockouts) is readily achieved by CRISPR/Cas9-mediated genome modification. Recently, exogenous DNA integration into the zebrafish genome via homology-independent DNA repair was reported, but this integration contained various mutations at the junctions of genomic and integrated DNA. Thus, precise genome modification into targeted genomic loci remains to be achieved. Here, we describe efficient, precise CRISPR/Cas9-mediated integration using a donor vector harbouring short homologous sequences (10-40 bp) flanking the genomic target locus. We succeeded in integrating with high efficiency an exogenous mCherry or eGFP gene into targeted genes (tyrosinase and krtt1c19e) in frame. We found the precise in-frame integration of exogenous DNA without backbone vector sequences when Cas9 cleavage sites were introduced at both sides of the left homology arm, the eGFP sequence and the right homology arm. Furthermore, we confirmed that this precise genome modification was heritable. This simple method enables precise targeted gene knock-in in zebrafish.

Sangivamycin induces apoptosis by suppressing Erk signaling in primary effusion lymphoma cells.

Sangivamycin, a structural analog of adenosine and antibiotic exhibiting antitumor and antivirus activities, inhibits protein kinase C and the synthesis of both DNA and RNA. Primary effusion lymphoma (PEL) is an aggressive neoplasm caused by Kaposi's sarcoma-associated herpesvirus (KSHV) in immunosuppressed patients and HIV-infected homosexual males. PEL cells are derived from post-germinal center B cells, and are infected with KSHV. Herein, we asked if sangivamycin might be useful to treat PEL. We found that sangivamycin killed PEL cells, and we explored the underlying mechanism. Sangivamycin treatment drastically decreased the viability of PEL cell lines compared to KSHV-uninfected B lymphoma cell lines. Sangivamycin induced the apoptosis of PEL cells by activating caspase-7 and -9. Further, sangivamycin suppressed the phosphorylation of Erk1/2 and Akt, thus inhibiting activation of the proteins. Inhibitors of Akt and MEK suppressed the proliferation of PEL cells compared to KSHV-uninfected cells. It is known that activation of Erk and Akt signaling inhibits apoptosis and promotes proliferation in PEL cells. Our data therefore suggest that sangivamycin induces apoptosis by inhibiting Erk and Akt signaling in such cells. We next investigated whether sangivamycin, in combination with an HSP90 inhibitor geldanamycin (GA) or valproate (valproic acid), potentiated the cytotoxic effects of the latter drugs on PEL cells. Compared to treatment with GA or valproate alone, the addition of sangivamycin enhanced cytotoxic activity. Our data thus indicate that sangivamycin may find clinical utility as a novel anti-cancer agent targeting PEL.

The effects of heat shock protein 90 inhibitors on apoptosis and viral replication in primary effusion lymphoma cells.

Primary effusion lymphoma (PEL) is an aggressive neoplasm caused by Kaposi's sarcoma-associated herpesvirus (KSHV) in immunosuppressed patients and human immunodeficiency virus (HIV)-infected homosexual males. We evaluated the cytotoxic effects of heat shock protein 90 (HSP90) inhibitors on PEL cells. The HSP90 inhibitors geldanamycin (GA), 17(allylamino)-17-demethoxygeldanamycin (17-AAG), and radicicol dramatically inhibited cell proliferation and induced apoptosis of PEL cells through caspase activation. Furthermore, GA induced the stabilization of inhibitor of κB (IκB)α and reduced the phosphorylation of IκBα in PEL cells. HSP90 inhibitors suppressed the transcriptional activity of nuclear factor-kappa B (NF-κB) in PEL cells. It is known that the constitutive activation of NF-κB signaling is essential for the survival of PEL cells and HSP90 contributes to promote activation of NF-κB signaling. The suppression of NF-κB signaling by HSP90 inhibitors may contribute to the induction of apoptosis in PEL cells. In addition, HSP90 activity is required for KSHV replication in KSHV latently infected PEL cells. GA, 17-AAG and radicicol reduced the production of progeny virus from PEL cells at low concentrations, which do not affect PEL cell growth. Our results suggest that HSP90 activity is required for both the survival of PEL cells and viral replication in PEL cells, and that pharmacologic inhibition of HSP90 may be an effective treatment for PEL and KSHV-related diseases.

The Ubiquitin System and Kaposi's Sarcoma-Associated Herpesvirus.

Ubiquitination is a post-translational modification in which one or more ubiquitin molecules are covalently linked to lysine residues of target proteins. The ubiquitin system plays a key role in the regulation of protein degradation, which contributes to cell signaling, vesicular trafficking, apoptosis, and immune regulation. Bacterial and viral pathogens exploit the cellular ubiquitin system by encoding their own proteins to serve their survival and replication in infected cells. Recent studies have revealed that Kaposi's sarcoma-associated herpesvirus (KSHV) manipulates the ubiquitin system of infected cells to facilitate cell proliferation, anti-apoptosis, and evasion from immunity. This review summarizes recent developments in our understanding of the molecular mechanisms used by KSHV to interact with the cellular ubiquitin machinery.

Isolation of desmosomes from the epidermis of Xenopus laevis and immunochemical characterization of the Xenopus desmosomal cadherins.

Here we report a new method of isolating epidermal desmosomes from Xenopus laevis, and a major constituent of desmosomes designated as Xenopus desmogleins (XDsg). Isolation of desmosomes from Xenopus laevis epidermis was carried out by a two step-incubation with different concentrations of NP-40. After discontinuous sucrose gradient centrifugation at 30,000 g for 60 min, a pure desmosomal fraction was obtained at 30%/40% interface. In the SDS-PAGE of isolated desmosomes, at least 12 bands (XDB1 to XDB12) were observed over a 75 kD region. Among them, three bands (XDB3, XDB7, XDB8; estimated MW 175, 124, and 112 kD respectively) were recognized as glycoproteins based on ConA binding. Monospecific polyclonal antibody against XDB3 cross-reacted with bovine Dsgs and vis-a-vis anti-bovine Dsgs with XDB3. By contrast, monospecific antibody against bovine Dsc a/b did not cross-react with either XDB7 or XDB8. Heterogeneous molecular constituents of desmosomal adhesion molecule, which have been observed among different bovine tissues, were confirmed in a phylogenetically different animal, Xenopus laevis. Combined results with other evidence could suggest an alternative system for desmosome-mediated cell adhesion.