Cloning and developmental expression of Xenopus Stat1

Proteomics of Xenopus development

Modern mass spectrometry-based methods provide an exciting opportunity to characterize protein expression in the developing embryo. We have employed an isotopic labeling technology to quantify the expression dynamics of nearly 6000 proteins across six stages of development in Xenopus laevis from the single stage zygote through the mid-blastula transition and the onset of organogenesis. Approximately 40% of the proteins show significant changes in expression across the development stages. The expression changes for these proteins naturally falls into six clusters corresponding to major events that mark early Xenopus development. A subset of experiments in this study have quantified protein expression differences between single embryos at the same stage of development, showing that, within experimental error, embryos at the same developmental stage have identical protein expression levels.

Quantitative proteomics of Xenopus laevis embryos: expression kinetics of nearly 4000 proteins during early development

While there is a rich literature on transcription dynamics during the development of many organisms, protein data is limited. We used iTRAQ isotopic labeling and mass spectrometry to generate the largest developmental proteomic dataset for any animal. Expression dynamics of nearly 4,000 proteins of Xenopuslaevis was generated from fertilized egg to neurula embryo. Expression clusters into groups. The cluster profiles accurately reflect the major events that mark changes in gene expression patterns during early Xenopus development. We observed decline in the expression of ten DNA replication factors after the midblastula transition (MBT), including a marked decline of the licensing factor XCdc6. Ectopic expression of XCdc6 leads to apoptosis; temporal changes in this protein are critical for proper development. Measurement of expression in single embryos provided no evidence for significant protein heterogeneity between embryos at the same stage of development.

Differential expression of STAT1 and IFN-γ in primary and invasive or metastatic wilms tumors

BACKGROUND AND OBJECTIVES

IFN/STAT1 signaling has been found to be not only associated with an aggressive tumor phenotype but also activated and functional during metanephric development. This study was undertaken to evaluate STAT1 and IFN-γ expression and its relation to histopathological features of primary and invasive/metastatic Wilms tumors.

METHODS

Immunohistochemistry was used to determine the expression and cellular distribution of STAT1 and IFN-γ in 18 pairs of primary and corresponding invasive/metastatic Wilms tumors and 40 primary tumors without invasion or metastasis.

RESULTS

Positive rate of STAT1/IFN-γ expression was 66.7%/61.1% and 72.2%/77.8% in 18 pairs of primary and associated invasive/metastatic Wilms tumor tissues, while 35.0%/27.5% in 40 primary tumors without invasion or metastasis. The expression of STAT1 and IFN-γ was significantly associated with invasion/metastasis (P = 0.025; P = 0.015). There was a positive correlation between STAT1 and IFN-γ expression in all Wilms tumor tissues (χ(2)  = 23.408, P = 0.05, r = 0.555). The expression of STAT1 and IFN-γ between primary and matched invasive/metastatic tissues was concordance, respectively (P = 0.710 and P = 0.375).

CONCLUSIONS

These results suggest that IFN-γ/STAT1 signaling might have clinical potential as a promising predictor to identify individuals with poor prognostic potential and as a possible novel target molecule of therapy for Wilms tumor.

Brain-specific promoter/exon I.f of the cyp19a1 (aromatase) gene in Xenopus laevis

Aromatase, encoded by the cyp19a1 gene, is the key enzyme for estrogen biosynthesis. Exon I.f of aromatase transcripts in the Xenopus brain is driven in a brain-specific manner. In this study, we cloned brain aromatase with a 5'-end of various lengths by 5'-RACE and detected the expression pattern of the aromatase mRNA. In Xenopus at the larval stage, the brain aromatase mRNA expression was five-fold higher than those in the gonad and liver, and was upregulated from stage 42 to stage 50. After isolating the brain-specific promoter I.f, which was located ∼6.5 kb upstream from gonad-specific exon PII, we observed this promoter in a potential cis-elements for several transcriptional factors, such as Oct-1, c-Myc, the GATA gene family, C/EBPalpha, Sox5, p300, XFD-1, AP1, the STAT gene family, FOXD3, and the Smad gene family. In addition, the core promoter elements of two initiators and an atypical TATA box were found around the 5'-RACE products. In the 5'-flanking region of exon I.f, the binding sites for nuclear extracts suggested that the followings are important: the STAT gene family, a 38-bp conserved region among five species, FOXD3, and the Smad gene family within the region 200 bp upstream from the transcription initiation site. Real-time RT-PCR analysis showed that the foxd3, smad2 and smad4.1/4.2 mRNAs are specifically expressed in the brain. Furthermore, the expression change of foxd3, which has been reported as a repressor, indicated that expression decreased to stage 50 from stage 42, contrary to that of aromatase mRNA. These results may imply that foxd3 expression decreases and aromatase expression increases as a result of the contribution to promoter I.f by transcriptional activators such as smads. However, since these putative cis-elements and transcription initiation sites are not conserved in the brain-specific promoter of other species, this transcriptional regulatory mechanism of exon I.f may be characteristic of Xenopus.

Dynamic expression profiles of virus-responsive and putative antimicrobial peptide-encoding transcripts during Atlantic cod (Gadus morhua) embryonic and early larval development

Early life stage mortality is one of the problems faced by Atlantic cod aquaculture. However, our understanding of immunity in early life stage fish is still incomplete, and the information available is restricted to a few species. In the present work we investigated the expression of immune-relevant transcripts in Atlantic cod during early development. The transcripts subjected to QPCR analysis in the present study were previously identified as putative anti-viral or anti-bacterial genes in Atlantic cod using suppression subtractive hybridization (SSH) libraries, QPCR, and/or microarrays. Of the 11 genes involved in this study, only atf3, cxc chemokine and gaduscidin-1 were not detected at the transcript level in all developmental stages investigated from unfertilized egg to early larval stage. Adam22, hamp, il8, irf1, irf7, lgp2, sacsin, and stat1 transcripts were detected in unfertilized egg and 7h post-fertilization (~2-cell stage) embryos, showing maternal contribution of these immune-relevant transcripts to the early embryonic transcriptome. The Atlantic cod genes included in this study presented diverse transcript expression profiles throughout embryonic and early larval development. For example, adam22 and sacsin transcripts rose abruptly during blastula/gastrula stage and were then expressed at relatively high levels through subsequent embryonic and early larval developmental stages. A peak in irf1 and irf7 transcript expression during early segmentation suggests that these interferon pathway genes play developmental stage-specific roles during cod embryogenesis. Stat1 had increasing transcript expression throughout blastula/gastrula, segmentation, and early larval developmental stages. Atf3, cxc chemokine, gaduscidin-1, and il8 transcripts rose approximately 2-3 fold during hatching, supporting the hypothesis that there is preparation at the immune-relevant transcript expression level to deal with environmental pathogens that may be encountered during early larval development. The specific roles that interferon pathway and other immune-relevant genes play in early life stage cod, and the potential impact of their dynamic transcript expression on immune competence of Atlantic cod embryos and larvae, remain unclear and warrant further study.

STAT1 activation regulates proliferation and differentiation of renal progenitors

We have shown previously that activation of STAT1 contributes to the pathogenesis of Wilms tumor. This neoplasm caricatures metanephric development and is believed to originate from embryonic renal mesenchymal progenitors that lose their ability to undergo mesenchymal-epithelial transition (MET). Therefore, we hypothesized that STAT1 is also activated and functional during metanephric development. Here we have demonstrated that both STAT1 and STAT3 are activated during normal development of the embryonic kidney. Furthermore, activation of STAT1 stimulated the proliferation of metanephric mesenchymal cells, but it prevented MET and tubulogenesis induced by leukemia inhibitory factor, which preferentially activates STAT3. Consistent with its negative regulation of metanephric mesenchymal differentiation, inhibition of STAT1 activation with protein kinase CK2 inhibitor TBB or RNAi-mediated knockdown of STAT1 promoted differentiation of metanephric progenitors and abolished the effect of cytokine-induced STAT1 activation in these cells. Additionally, a cell-permeable peptide that inhibits STAT1-mediated transactivation by targeting the STAT1 N-domain also blocked cytokine-induced STAT1-dependent proliferation in metanephric progenitors and promoted LIF-induced MET and tubulogenesis. Finally, the STAT1 peptide inhibitor caused the down regulation of survival/anti-apoptotic factors, Mcl-1 and Hsp-27, and induced apoptosis in renal tumor cells with constitutively active STAT1, indicating that STAT1 is required for these cells to survive. These findings show that both metanephric progenitors and renal tumor cells utilize a STAT1-dependent mechanism for growth or survival.

Functional analysis of Rousettus aegyptiacus "signal transducer and activator of transcription 1" (STAT1)

Bats are now known as the source of several diseases in humans, but few studies regarding immune responses and factors associated with bats have so far been reported. In this study, we focused on STAT1, one of the critical components in interferon (IFN)-signaling and antiviral activity, which is often targeted by viral proteins to reduce antiviral activity and increase viral replication. We found that Rousettus aegyptiacus STAT1 (bat STAT1) is phosphorylatable and translocates to the nucleus when stimulated with human IFN-alpha (hIFN-alpha). Furthermore, phosphorylation of bat STAT1 and inhibition of nuclear translocation was observed in IFN-stimulated cells infected with the HEP-Flury strain of rabies virus, in the same manner as in other mammals. Additionally, quantitative real-time RT-PCR revealed that bat STAT1 mRNA was highly expressed in the liver, while low in muscle and spleen.

STAT5A/B activity is required in the developing forebrain and spinal cord

Formation of the CNS requires the coordination and integration of processes such as cell proliferation, neuronal differentiation, neuronal migration, axon tract formation and synaptogenesis, all of which must occur at precise times and places during development. Although growth factors are known to play a role in regulating many of these processes, very little is known of the signaling events immediately downstream of ligand-receptor interactions in the developing CNS. Here we present evidence that STAT5, an important mediator of cytokine signaling, is required for some aspects of CNS development. We show that phosphorylated and hence activated forms of STAT5 (pSTAT5) are expressed in a temporally restricted manner in a subset of early-born telencephalic neurons and axons. Accordingly, Stat5 mutants have reduced numbers of interneurons in the cortical marginal zone, suggestive of migration defects. Moreover, corticofugal axons develop aberrantly in Stat5 mutants, indicative of a role for pSTAT5 in axon guidance. Notably, pSTAT5 is also expressed in commissural axons in the embryonic spinal cord, where it is also required for their guidance. Taken together, we provide the first evidence that STAT5 is a key effector molecule in the developing mammalian CNS.

STAT5 acts as a repressor to regulate early embryonic erythropoiesis

STAT5 regulates definitive (adult stage) erythropoiesis through its ability to transduce signals from the erythropoietin receptor. A function for STAT-dependent signaling during primitive (embryonic) erythropoiesis has not been analyzed. We tested this in the Xenopus system, because STAT5 is expressed at the right time and place to regulate development of the embryonic primitive ventral blood island. Depletion of STAT5 activity results in delayed accumulation of the first globin-expressing cells, indicating that the gene does regulate primitive erythropoiesis. Our results suggest that in this context STAT5 functions as a repressor, since forced expression of an activator isoform blocks erythropoiesis, while embryos expressing a repressor isoform develop normally. The erythroid phenotype caused by the activator isoform of STAT5 resembles that caused by overexpression of fibroblast growth factor (FGF). We show that STAT5 isoforms can function epistatic to FGF and can be phosphorylated in response to hyperactivated FGF signaling in Xenopus embryos. Therefore, our data indicate that STAT5 functions in both primitive and definitive erythropoiesis, but by different mechanisms.

The ins and outs of STAT1 nuclear transport

There is an inherent elegance in being in the right place at the right time. The STAT1 transcription factor possesses regulatory signals that ensure its distribution to the right cellular location at the right time. Latent STAT1 resides primarily in the cytoplasm, and there it responds to hormone signaling through tyrosine phosphorylation by Janus kinases or growth factor receptors. After phosphorylation, STAT1 dimerizes, and this conformational change reveals a nuclear import signal that is recognized by a specific nuclear import carrier. In the nucleus, the STAT1 dimer dissociates from the import carrier and binds to specific DNA target sites in the promoters of regulated genes. STAT1 is subsequently dephosphorylated in the nucleus by a constitutively active tyrosine phosphatase, leading to its dissociation from DNA. A nuclear export signal of STAT1 appears to be masked when dimers are bound to DNA, but it becomes accessible to the CRM1 export carrier after dissociation from DNA. CRM1 binds STAT1 and transports the transcription factor back to the cytoplasm. Studies show that the regulatory trafficking signals that guide the nuclear import and export of STAT1 reside within its DNA binding domain. The location of these signals indicates that their function has coevolved with the ability of STAT1 to bind DNA and regulate gene expression. The nuclear import and subsequent recycling of STAT1 to the cytoplasm are integral to its function as a signal transducer and activator of transcription.