Long-range axonal projections of transplanted mouse embryonic stem cell-derived hypothalamic neurons into adult mouse brain.

The hypothalamus is comprised of heterogenous cell populations and includes highly complex neural circuits that regulate the autonomic nerve system. Its dysfunction therefore results in severe endocrine disorders. Although recent experiments have been conducted for in vitro organogenesis of hypothalamic neurons from embryonic stem (ES) or induced pluripotent stem (iPS) cells, whether these stem cell-derived hypothalamic neurons can be useful for regenerative medicine remains unclear. We therefore performed orthotopic transplantation of mouse ES cell (mESC)-derived hypothalamic neurons into adult mouse brains. We generated electrophysiologically functional hypothalamic neurons from mESCs and transplanted them into the supraoptic nucleus of mice. Grafts extended their axons along hypothalamic nerve bundles in host brain, and some of them even projected into the posterior pituitary (PPit), which consists of distal axons of the magnocellular neurons located in hypothalamic supraoptic and paraventricular nuclei. The axonal projections to the PPit were not observed when the mESC-derived hypothalamic neurons were ectopically transplanted into the substantia nigra reticular part. These findings suggest that our stem cell-based orthotopic transplantation approach might contribute to the establishment of regenerative medicine for hypothalamic and pituitary disorders.

EpCAM Is a Surface Marker for Enriching Anterior Pituitary Cells From Human Hypothalamic-Pituitary Organoids.

Human stem cell-derived organoid culture enables the in vitro analysis of the cellular function in three-dimensional aggregates mimicking native organs, and also provides a valuable source of specific cell types in the human body. We previously established organoid models of the hypothalamic-pituitary (HP) complex using human pluripotent stem cells. Although the models are suitable for investigating developmental and functional HP interactions, we consider that isolated pituitary cells are also useful for basic and translational research on the pituitary gland, such as stem cell biology and regenerative medicine. To develop a method for the purification of pituitary cells in HP organoids, we performed surface marker profiling of organoid cells derived from human induced pluripotent stem cells (iPSCs). Screening of 332 human cell surface markers and a subsequent immunohistochemical analysis identified epithelial cell adhesion molecule (EpCAM) as a surface marker of anterior pituitary cells, as well as their ectodermal precursors. EpCAM was not expressed on hypothalamic lineages; thus, anterior pituitary cells were successfully enriched by magnetic separation of EpCAM+ cells from iPSC-derived HP organoids. The enriched pituitary population contained functional corticotrophs and their progenitors; the former responded normally to a corticotropin-releasing hormone stimulus. Our findings would extend the applicability of organoid culture as a novel source of human anterior pituitary cells, including stem/progenitor cells and their endocrine descendants.

Characterization of Hypothalamic MCH Neuron Development in a 3D Differentiation System of Mouse Embryonic Stem Cells.

Hypothalamic melanin-concentrating hormone (MCH) neurons are important regulators of multiple physiological processes, such as sleep, feeding, and memory. Despite the increasing interest in their neuronal functions, the molecular mechanism underlying MCH neuron development remains poorly understood. We report that a three-dimensional culture of mouse embryonic stem cells (mESCs) can generate hypothalamic-like tissues containing MCH-positive neurons, which reproduce morphologic maturation, neuronal connectivity, and neuropeptide/neurotransmitter phenotype of native MCH neurons. Using this in vitro system, we demonstrate that Hedgehog (Hh) signaling serves to produce major neurochemical subtypes of MCH neurons characterized by the presence or absence of cocaine- and amphetamine-regulated transcript (CART). Without exogenous Hh signals, mESCs initially differentiated into dorsal hypothalamic/prethalamic progenitors and finally into MCH+CART+ neurons through a specific intermediate progenitor state. Conversely, activation of the Hh pathway specified ventral hypothalamic progenitors that generate both MCH+CART- and MCH+CART+ neurons. These results suggest that in vivo MCH neurons may originate from multiple cell lineages that arise through early dorsoventral patterning of the hypothalamus. Additionally, we found that Hh signaling supports the differentiation of mESCs into orexin/hypocretin neurons, a well-defined cell group intermingled with MCH neurons in the lateral hypothalamic area (LHA). The present study highlights and improves the utility of mESC culture in the analysis of the developmental programs of specific hypothalamic cell types.

Epstein-Barr Virus Enhances Cancer-Specific Aberrant Splicing of TSG101 Pre-mRNA.

Tumor viruses gain control of cellular functions when they infect and transform host cells. Alternative splicing is one of the cellular processes exploited by tumor viruses to benefit viral replication and support oncogenesis. Epstein-Barr virus (EBV) participates in a number of cancers, as reported mostly in nasopharyngeal carcinoma (NPC) and Burkitt lymphoma (BL). Using RT-nested-PCR and Northern blot analysis in NPC and BL cells, here we demonstrate that EBV promotes specific alternative splicing of TSG101 pre-mRNA, which generates the TSG101∆154-1054 variant though the agency of its viral proteins, such as EBNA-1, Zta and Rta. The level of TSG101∆154-1054 is particularly enhanced upon EBV entry into the lytic cycle, increasing protein stability of TSG101 and causing the cumulative synthesis of EBV late lytic proteins, such as VCA and gp350/220. TSG101∆154-1054-mediated production of VCA and gp350/220 is blocked by the overexpression of a translational mutant of TSG101∆154-1054 or by the depletion of full-length TSG101, which is consistent with the known role of the TSG101∆154-1054 protein in stabilizing the TSG101 protein. NPC patients whose tumor tissues express TSG101∆154-1054 have high serum levels of anti-VCA antibodies and high levels of viral DNA in their tumors. Our findings highlight the functional importance of TSG101∆154-1054 in allowing full completion of the EBV lytic cycle to produce viral particles. We propose that targeting EBV-induced TSG101 alternative splicing has broad potential as a therapeutic to treat EBV-associated malignancies.

The Exon Junction Complex Core Represses Cancer-Specific Mature mRNA Re-splicing: A Potential Key Role in Terminating Splicing.

Using TSG101 pre-mRNA, we previously discovered cancer-specific re-splicing of mature mRNA that generates aberrant transcripts/proteins. The fact that mRNA is aberrantly re-spliced in various cancer cells implies there must be an important mechanism to prevent deleterious re-splicing on the spliced mRNA in normal cells. We thus postulated that mRNA re-splicing is controlled by specific repressors, and we searched for repressor candidates by siRNA-based screening for mRNA re-splicing activity. We found that knock-down of EIF4A3, which is a core component of the exon junction complex (EJC), significantly promoted mRNA re-splicing. Remarkably, we could recapitulate cancer-specific mRNA re-splicing in normal cells by knock-down of any of the core EJC proteins, EIF4A3, MAGOH, or RBM8A (Y14), implicating the EJC core as the repressor of mRNA re-splicing often observed in cancer cells. We propose that the EJC core is a critical mRNA quality control factor to prevent over-splicing of mature mRNA.

The Bartonella autotransporter BafA activates the host VEGF pathway to drive angiogenesis.

Pathogenic bacteria of the genus Bartonella can induce vasoproliferative lesions during infection. The underlying mechanisms are unclear, but involve secretion of an unidentified mitogenic factor. Here, we use functional transposon-mutant screening in Bartonella henselae to identify such factor as a pro-angiogenic autotransporter, called BafA. The passenger domain of BafA induces cell proliferation, tube formation and sprouting of microvessels, and drives angiogenesis in mice. BafA interacts with vascular endothelial growth factor (VEGF) receptor-2 and activates the downstream signaling pathway, suggesting that BafA functions as a VEGF analog. A BafA homolog from a related pathogen, Bartonella quintana, is also functional. Our work unveils the mechanistic basis of vasoproliferative lesions observed in bartonellosis, and we propose BafA as a key pathogenic factor contributing to bacterial spread and host adaptation.

Cancer-Specifically Re-Spliced TSG101 mRNA Promotes Invasion and Metastasis of Nasopharyngeal Carcinoma.

TSG101 (Tumor susceptibility 101) gene and its aberrantly spliced isoform, termed TSG101∆154-1054, are tightly linked to tumorigenesis in various cancers. The aberrant TSG101∆154-1054 mRNA is generated from cancer-specific re-splicing of mature TSG101 mRNA. The TSG101∆154-1054 protein protects the full-length TSG101 protein from ubiquitin-mediated degradation, implicating TSG101∆154-1054 protein in the progression of cancer. Here, we confirmed that the presence of TSG101∆154-1054 mRNA indeed caused an accumulation of the TSG101 protein in biopsies of human nasopharyngeal carcinoma (NPC), which was recapitulated by the overexpression of TSG101∆154-1054 in the NPC cell line TW01. We demonstrate the potential function of the TSG101∆154-1054 protein in the malignancy of human NPC with scratch-wound healing and transwell invasion assays. By increasing the stability of the TSG101 protein, TSG101∆154-1054 specifically enhanced TSG101-mediated TW01 cell migration and invasion, suggesting the involvement in NPC metastasis in vivo. This finding sheds light on the functional significance of TSG101∆154-1054 generation via re-splicing of TSG101 mRNA in NPC metastasis and hints at its potential importance as a therapeutic target.

Rearrangement of VPS13B, a causative gene of Cohen syndrome, in a case of RUNX1-RUNX1T1 leukemia with t(8;12;21).

Variant chromosomal translocations associated with t(8;21) are observed in 3-4% of acute myeloid leukemia (AML) cases with a RUNX1-RUNX1T1 fusion gene. However, the molecular events that occur in variants of t(8;21) are not well characterized. In the present study, we report genetic features of a variant three-way translocation of t(8;12;21)(q22;p11;q22) in a patient with AML. In this patient, leukemia cells lacked azurophilic granules, which does not correspond with the classic features of t(8;21). RNA-seq analysis revealed that TM7SF3 at 12p11 was fused to VPS13B at 8q22 and VPS13B to RUNX1, in addition to RUNX1-RUNX1T1. VPS13B was located near RUNX1T1 and both were localized at the same chromosomal bands. The reading frames of TM7SF3 and VPS13B did not match to those of VPS13B and RUNX1, respectively. Disruption of VPS13B causes Cohen syndrome, which presents intermittent neutropenia with a left-shifted granulopoiesis in the bone marrow. Disruption of VPS13B may thus cause the unusual features of RUNX1-RUNX1T1 leukemia. Our case indicates that rearrangement of VPS13B may be additional genetic events in variant t(8;21).

Endogenous Multiple Exon Skipping and Back-Splicing at the DMD Mutation Hotspot.

Duchenne muscular dystrophy (DMD) is a severe muscular disorder. It was reported that multiple exon skipping (MES), targeting exon 45-55 of the DMD gene, might improve patients' symptoms because patients who have a genomic deletion of all these exons showed very mild symptoms. Thus, exon 45-55 skipping treatments for DMD have been proposed as a potential clinical cure. Herein, we detected the expression of endogenous exons 44-56 connected mRNA transcript of the DMD using total RNAs derived from human normal skeletal muscle by reverse transcription polymerase chain reaction (RT-PCR), and identified a total of eight types of MES products around the hotspot. Surprisingly, the 5' splice sites of recently reported post-transcriptional introns (remaining introns after co-transcriptional splicing) act as splicing donor sites for MESs. We also tested exon combinations to generate DMD circular RNAs (circRNAs) and determined the preferential splice sites of back-splicing, which are involved not only in circRNA generation, but also in MESs. Our results fit the current circRNA-generation model, suggesting that upstream post-transcriptional introns trigger MES and generate circRNA because its existence is critical for the intra-intronic interaction or for extremely distal splicing.

ETV6-LPXN fusion transcript generated by t(11;12)(q12.1;p13) in a patient with relapsing acute myeloid leukemia with NUP98-HOXA9.

ETV6, which encodes an ETS family transcription factor, is frequently rearranged in human leukemias. We show here that a patient with acute myeloid leukemia with t(7;11)(p15;p15) gained, at the time of relapse, t(11;12)(q12.1;p13) with a split ETV6 FISH signal. Using 3'-RACE PCR analysis, we found that ETV6 was fused to LPXN at 11q12.1, which encodes leupaxin. ETV6-LPXN, an in-frame fusion between exon 4 of ETV6 and exon 2 of LPXN, did not transform the interleukin-3-dependent 32D myeloid cell line to cytokine independence; however, an enhanced proliferative response was observed when these cells were treated with G-CSF without inhibition of granulocytic differentiation. The 32D and human leukemia cell lines each transduced with ETV6-LPXN showed enhanced migration towards the chemokine CXCL12. We show here for the first time that LPXN is a fusion partner of ETV6 and present evidence indicating that ETV6-LPXN plays a crucial role in leukemia progression through enhancing the response to G-CSF and CXCL12.

NUP214-RAC1 and RAC1-COL12A1 Fusion in Complex Variant Translocations Involving Chromosomes 6, 7 and 9 in an Acute Myeloid Leukemia Case with DEK-NUP214.

DEK-NUP214 gene fusion in acute myeloid leukemia (AML) is associated with poor prognosis. It is most often a sole translocation and more rarely observed as complex chromosomal forms. We describe an AML case with complex karyotype abnormalities involving chromosome bands 6p23, 6q13, 7p22, and 9q34. RNA sequencing analysis revealed that exon 17 of NUP214 (9q34) was fused to exon 2 of RAC1 (7p22). We also detected that the 5'-end of intron 1 of RAC1 was fused with the antisense strand of intron 5 of COL12A1 (6q13). RT-PCR analysis confirmed the expression of DEK-NUP214, NUP214-RAC1, RAC1-COL12A1, NUP214, and RAC1. These results suggest that the 5'- and 3'-ends of NUP214 from the breakpoint in the same locus were fused to RAC1 and DEK, respectively, and the 5'-end of RAC1 was fused to COL12A1. The reading frame of NUP214 was not matched with RAC1; however, high expression of the RAC1 protein was detected by Western blotting. This study identifies the variant complex fusion genesNUP214-RAC1 and RAC1- COL12A1 in a case of AML.

Fluvoxamine moderates reduced voluntary activity following chronic dexamethasone infusion in mice via recovery of BDNF signal cascades.

Major depression is a complex disorder characterized by genetic and environmental interactions. Selective serotonin reuptake inhibitors (SSRIs) effectively treat depression. Neurogenesis following chronic antidepressant treatment activates brain derived neurotrophic factor (BDNF) signaling. In this study, we analyzed the effects of the SSRI fluvoxamine (Flu) on locomotor activity and forced-swim behavior using chronic dexamethasone (cDEX) infusions in mice, which engenders depression-like behavior. Infusion of cDEX decreased body weight and produced a trend towards lower locomotor activity during darkness. In the forced-swim test, cDEX-mice exhibited increased immobility times compared with mice administered saline. Flu treatment reversed decreased locomotor activity and mitigated forced-swim test immobility. Real-time polymerase chain reactions using brain RNA samples yielded significantly lower BDNF mRNA levels in cDEX-mice compared with the saline group. Endoplasmic reticulum stress-associated X-box binding protein-1 (XBP1) gene expression was lower in cDEX-mice compared with the saline group. However, marked expression of the XBP1 gene was observed in cDEX-mice treated with Flu compared with mice given saline and untreated cDEX-mice. Expression of 5-HT2A and Sigma-1 receptors decreased after cDEX infusion compared with the saline group, and these decreases normalized to control levels upon Flu treatment. Our results indicate that the Flu moderates reductions in voluntary activity following chronic dexamethasone infusions in mice via recovery of BDNF signal cascades.

Spatiotemporal expression pattern of Myt/NZF family zinc finger transcription factors during mouse nervous system development.

BACKGROUND: Three members of the Myt/NZF family of transcription factors are involved in many processes of vertebrate development. Several studies have reported that Myt1/NZF-2 has a regulatory function in the development of cultured oligodendrocyte progenitors or in neuronal differentiation during Xenopus primary neurogenesis. However, little is known about the proper function of Myt/NZF family proteins during mammalian nervous system development. To assess the possible function of Myt/NZF transcription factors in mammalian neuronal differentiation, we determined the comparative spatial and temporal expression patterns of all three types of Myt/NZF family genes in the embryonic mouse nervous system using quantitative reverse transcriptase polymerase chain reaction and in situ hybridization. RESULTS: All three Myt/NZF family genes were extensively expressed in developing mouse nervous tissues, and their expression was transient. NZF-1 was expressed later in post-mitotic neurons. NZF-2 was initially expressed in neuronal cells a little earlier than NZF-3. NZF-3 was initially expressed in neuronal cells, just after proliferation was complete. CONCLUSION: These expression patterns suggest that the expression of NZF family genes is spatially and temporally regulated, and each Myt/NZF family gene may have a regulatory function in a specific phase during neuronal differentiation.

Nested introns in an intron: evidence of multi-step splicing in a large intron of the human dystrophin pre-mRNA.

The mechanisms by which huge human introns are spliced out precisely are poorly understood. We analyzed large intron 7 (110199 nucleotides) generated from the human dystrophin (DMD) pre-mRNA by RT-PCR. We identified branching between the authentic 5' splice site and the branch point; however, the sequences far from the branch site were not detectable. This RT-PCR product was resistant to exoribonuclease (RNase R) digestion, suggesting that the detected lariat intron has a closed loop structure but contains gaps in its sequence. Transient and concomitant generation of at least two branched fragments from nested introns within large intron 7 suggests internal nested splicing events before the ultimate splicing at the authentic 5' and 3' splice sites. Nested splicing events, which bring the authentic 5' and 3' splice sites into close proximity, could be one of the splicing mechanisms for the extremely large introns.

Re-splicing of mature mRNA in cancer cells promotes activation of distant weak alternative splice sites.

Transcripts of the human tumor susceptibility gene 101 (TSG101) are aberrantly spliced in many cancers. A major aberrant splicing event on the TSG101 pre-mRNA involves joining of distant alternative 5' and 3' splice sites within exon 2 and exon 9, respectively, resulting in the extensive elimination of the mRNA. The estimated strengths of the alternative splice sites are much lower than those of authentic splice sites. We observed that the equivalent aberrant mRNA could be generated from an intron-less TSG101 gene expressed ectopically in breast cancer cells. Remarkably, we identified a pathway-specific endogenous lariat RNA consisting solely of exonic sequences, predicted to be generated by a re-splicing between exon 2 and exon 9 on the spliced mRNA. Our results provide evidence for a two-step splicing pathway in which the initial constitutive splicing removes all 14 authentic splice sites, thereby bringing the weak alternative splice sites into close proximity. We also demonstrate that aberrant multiple-exon skipping of the fragile histidine triad (FHIT) pre-mRNA in cancer cells occurs via re-splicing of spliced FHIT mRNA. The re-splicing of mature mRNA can potentially generate mutation-independent diversity in cancer transcriptomes. Conversely, a mechanism may exist in normal cells to prevent potentially deleterious mRNA re-splicing events.

Myt/NZF family transcription factors regulate neuronal differentiation of P19 cells.

During mammalian central nervous system development, neural stem cells differentiate and then mature into various types of neurons. Myelin transcription factor (Myt)/neural zinc finger (NZF) family proteins were first identified as myelin proteolipid protein promoter binding factors and were shown to be involved in oligodendrocyte development. In this study, we found that Myt/NZF family molecules were expressed during neuronal differentiation in vivo and in vitro. Transient over-expression of Myt/NZF family genes could convert undifferentiated P19 cells into neurons without induction by retinoic acid (RA), and the ability of these genes to induce neuronal differentiation was comparable to that of Neurog1 and Neurod1. Additionally, we found that St18 (or NZF-3) was induced by several bHLH transcription factors. When NZF-3 and Neurog1 were co-expressed in P19 cells, the rate of neuronal differentiation was significantly increased. These data suggest not only that NZF-3 works downstream of Neurog1 but also that it plays a crucial role together with Neurog1 in neuronal differentiation.

NZF-2b is a novel predominant form of mouse NZF-2/MyT1, expressed in differentiated neurons especially at higher levels in newly generated ones.

NZF-2 (MyT1) is a member of C2HC-type zinc finger transcription factors. A novel form of mouse NZF-2 has been isolated. This novel form, NZF-2b, has an additional C2HC-type zinc finger motif. The expression levels of NZF-2b are by far the more predominant than those of the already known form of NZF-2. In embryonic mouse nervous system, the expression of NZF-2b starts as early as at 9.5 days post-coitum (dpc) in newly differentiated neurons in the central nervous system (CNS) and the peripheral nervous system (PNS).