Interactions between SOX factors and Wnt/beta-catenin signaling in development and disease

The SOX family of transcription factors have emerged as modulators of canonical Wnt/beta-catenin signaling in diverse development and disease contexts. There are over 20 SOX proteins encoded in the vertebrate genome and recent evidence suggests that many of these can physically interact with beta-catenin and modulate the transcription of Wnt-target genes. The precise mechanisms by which SOX proteins regulate beta-catenin/TCF activity are still being resolved and there is evidence to support a number of models including: protein-protein interactions, the binding of SOX factors to Wnt-target gene promoters, the recruitment of co-repressors or co-activators, modulation of protein stability, and nuclear translocation. In some contexts, Wnt signaling also regulates SOX expression resulting in feedback regulatory loops that fine-tune cellular responses to beta-catenin/TCF activity. In this review, we summarize the examples of Sox-Wnt interactions and examine the underlying mechanisms of this potentially widespread and underappreciated mode of Wnt-regulation.

Unraveling the transcriptional regulatory machinery in chondrogenesis

Since the discovery of SOX9 mutations in the severe human skeletal malformation syndrome campomelic dysplasia in 1994, Sox9 was shown to be both required and sufficient for chondrocyte specification and differentiation. At the same time, its distant relatives Sox5 and Sox6 were shown to act in redundancy with each other to robustly enhance its functions. The Sox trio is currently best known for its ability to activate the genes for cartilage-specific extracellular matrix components. Sox9 and Sox5/6 homodimerize through domains adjacent to their Sry-related high-mobility-group DNA-binding domain to increase the efficiency of their cooperative binding to chondrocyte-specific enhancers. Sox9 possesses a potent transactivation domain and thereby recruits diverse transcriptional co-activators, histone-modifying enzymes, subunits of the mediator complex, and components of the general transcriptional machinery, such as CBP/p300, Med12, Med25, and Wwp2. This information helps us begin to unravel the mechanisms responsible for Sox9-mediated transcription. We review here the discovery of this master chondrogenic trio and its roles in chondrogenesis in vivo and at the molecular level, and we discuss how these pioneering studies open the way for many additional studies that are needed to further increase our understanding of the transcriptional regulatory machinery operating in chondrogenesis.

Sox proteins in melanocyte development and melanoma

Over 10 years have passed since the first Sox gene was implicated in melanocyte development. Since then, we have discovered that SOX5, SOX9, SOX10 and SOX18 all participate as transcription factors that affect key melanocytic genes in both regulatory and modulatory fashions. Both SOX9 and SOX10 play major roles in the establishment and normal function of the melanocyte; SOX10 has been shown to heavily influence melanocyte development and SOX9 has been implicated in melanogenesis in the adult. Despite these advances, the precise cellular and molecular details of how these SOX proteins are regulated and interact during all stages of the melanocyte life cycle remain unknown. Improper regulation of SOX9 or SOX10 is also associated with cancerous transformation, and thus understanding the normal function of SOX proteins in the melanocyte will be key to revealing how these proteins contribute to melanoma.

B1 SOX coordinate cell specification with patterning and morphogenesis in the early zebrafish embryo

The B1 SOX transcription factors SOX1/2/3/19 have been implicated in various processes of early embryogenesis. However, their regulatory functions in stages from the blastula to early neurula remain largely unknown, primarily because loss-of-function studies have not been informative to date. In our present study, we systematically knocked down the B1 sox genes in zebrafish. Only the quadruple knockdown of the four B1 sox genes sox2/3/19a/19b resulted in very severe developmental abnormalities, confirming that the B1 sox genes are functionally redundant. We characterized the sox2/3/19a/19b quadruple knockdown embryos in detail by examining the changes in gene expression through in situ hybridization, RT–PCR, and microarray analyses. Importantly, these phenotypic analyses revealed that the B1 SOX proteins regulate the following distinct processes: (1) early dorsoventral patterning by controlling bmp2b/7; (2) gastrulation movements via the regulation of pcdh18a/18b and wnt11, a non-canonical Wnt ligand gene; (3) neural differentiation by regulating the Hes-class bHLH gene her3 and the proneural-class bHLH genes neurog1 (positively) and ascl1a (negatively), and regional transcription factor genes, e.g., hesx1, zic1, and rx3; and (4) neural patterning by regulating signaling pathway genes, cyp26a1 in RA signaling, oep in Nodal signaling, shh, and mdkb. Chromatin immunoprecipitation analysis of the her3, hesx1, neurog1, pcdh18a, and cyp26a1 genes further suggests a direct regulation of these genes by B1 SOX. We also found an interesting overlap between the early phenotypes of the B1 sox quadruple knockdown embryos and the maternal-zygotic spg embryos that are devoid of pou5f1 activity. These findings indicate that the B1 SOX proteins control a wide range of developmental regulators in the early embryo through partnering in part with Pou5f1 and possibly with other factors, and suggest that the B1 sox functions are central to coordinating cell fate specification with patterning and morphogenetic processes occurring in the early embryo.

In the developing embryo, various processes such as cell fate specification, embryo patterning, and morphogenesis take place concurrently. The embryo must control gene expression in order to coordinate these processes and thereby enable the proper organization of its structures. The B1 sox transcription factor genes, exemplified by the “stem cell gene” sox2, are thought to play a key role in these embryonic processes from the blastoderm stage to the neural stage. However, the precise regulatory functions of these genes are largely unknown due to the lack of loss-of-function studies. In our current study, we took advantage of the zebrafish system and successfully depleted B1 sox activity from the early embryo using antisense knockdown technology. This approach enabled us to further uncover the regulatory functions of B1 sox in early embryos. We found that the activity of the B1 sox genes is required for the expression of a wide range of developmental regulators including transcription factors, signaling pathway components, and cell adhesion molecules. These findings suggest that the B1 sox functions are central to coordinating diverse embryonic processes, particularly those that occur during the development of the primordium of the central nervous system.

Inhibition of Apoptosis Overcomes Stage-Related Compatibility Barriers to Chimera Formation in Mouse Embryos

Cell types more advanced in development than embryonic stem cells, such as EpiSCs, fail to contribute to chimeras when injected into pre-implantation-stage blastocysts, apparently because the injected cells undergo apoptosis. Here we show that transient promotion of cell survival through expression of the anti-apoptotic gene BCL2 enables EpiSCs and Sox17⁺ endoderm progenitors to integrate into blastocysts and contribute to chimeric embryos. Upon injection into blastocyst, BCL2-expressing EpiSCs contributed to all bodily tissues in chimeric animals while Sox17⁺ endoderm progenitors specifically contributed in a region-specific fashion to endodermal tissues. In addition, BCL2 expression enabled rat EpiSCs to contribute to mouse embryonic chimeras, thereby forming interspecies chimeras that could survive to adulthood. Our system therefore provides a method to overcome cellular compatibility issues that typically restrict chimera formation. Application of this type of approach could broaden the use of embryonic chimeras, including region-specific chimeras, for basic developmental biology research and regenerative medicine.

Multifactorial origins of heart and gut defects in nipbl-deficient zebrafish, a model of Cornelia de Lange Syndrome

Cornelia de Lange Syndrome (CdLS) is the founding member of a class of multi-organ system birth defect syndromes termed cohesinopathies, named for the chromatin-associated protein complex cohesin, which mediates sister chromatid cohesion. Most cases of CdLS are caused by haploinsufficiency for Nipped-B-like (Nipbl), a highly conserved protein that facilitates cohesin loading. Consistent with recent evidence implicating cohesin and Nipbl in transcriptional regulation, both CdLS cell lines and tissues of Nipbl-deficient mice show changes in the expression of hundreds of genes. Nearly all such changes are modest, however--usually less than 1.5-fold--raising the intriguing possibility that, in CdLS, severe developmental defects result from the collective action of many otherwise innocuous perturbations. As a step toward testing this hypothesis, we developed a model of nipbl-deficiency in zebrafish, an organism in which we can quantitatively investigate the combinatorial effects of gene expression changes. After characterizing the structure and embryonic expression of the two zebrafish nipbl genes, we showed that morpholino knockdown of these genes produces a spectrum of specific heart and gut/visceral organ defects with similarities to those in CdLS. Analysis of nipbl morphants further revealed that, as early as gastrulation, expression of genes involved in endodermal differentiation (sox32, sox17, foxa2, and gata5) and left-right patterning (spaw, lefty2, and dnah9) is altered. Experimental manipulation of the levels of several such genes--using RNA injection or morpholino knockdown--implicated both additive and synergistic interactions in causing observed developmental defects. These findings support the view that birth defects in CdLS arise from collective effects of quantitative changes in gene expression. Interestingly, both the phenotypes and gene expression changes in nipbl morphants differed from those in mutants or morphants for genes encoding cohesin subunits, suggesting that the transcriptional functions of Nipbl cannot be ascribed simply to its role in cohesin loading.

The Yin and Yang of Sox proteins: Activation and repression in development and disease

The general view of development consists of the acquisition of committed/differentiated phenotypes following a period of self-renewal and progenitor expansion. Lineage specification and progression are phenomena of antagonistic events, silencing tissue-specific gene expression in precursors to allow self-renewal and multipotentiality, and subsequently suppressing proliferation and embryonic gene expression to promote the restricted expression of tissue-specific genes during maturation. The high mobility group-containing Sox family of transcription factors constitutes one of the earliest classes of genes to be expressed during embryonic development. These proteins not only are indispensable for progenitor cell specification but also are critical for terminal differentiation of multiple cell types in a wide variety of lineages. Sox transcription factors are now known to induce or repress progenitor cell characteristics and cell proliferation or to activate the expression of tissue-specific genes. Sox proteins fulfill their diverse functions in developmental regulation by distinct molecular mechanisms. Not surprisingly, in addition to DNA binding and bending, Sox transcription factors also interact with different protein partners to function as coactivators or corepressors of downstream target genes. Here we seek to provide an overview of the current knowledge of Sox gene functional mechanisms, in an effort to understand their roles in both development and pathology.

Glioblastoma Stem Cells Respond to Differentiation Cues but Fail to Undergo Commitment and Terminal Cell-Cycle Arrest

Glioblastoma (GBM) is an aggressive brain tumor whose growth is driven by stemcell-like cells. BMP signaling triggers cell-cycle exit and differentiation of GBM stemcells (GSCs) and, therefore, might have therapeutic value. However, the epigenetic mechanisms that accompany differentiation remain poorly defined. It is also unclear whether cell-cycle arrest is terminal. Herewe find only a subset ofGSCcultures exhibit astrocyte differentiation in response to BMP. Although overtly differentiated non-cycling astrocytes are generated, they remain vulnerable to cell-cycle re-entry and fail to appropriately reconfigure DNA methylation patterns. Chromatin accessibility mapping identified loci that failed to alter in response to BMP and these were enriched in SOX transcription factor-binding motifs. SOX transcription factors, therefore, may limit differentiation commitment. A similar propensity for cell-cycle re-entry and de-differentiation was observed in GSC-derived oligodendrocyte-like cells. These findings highlight significant obstacles to BMP-induced differentiation as therapy forGBM.

SOX trio-co-transduced adipose stem cells in fibrin gel to enhance cartilage repair and delay the progression of osteoarthritis in the rat

The aim of this study was to test the hypotheses that retroviral gene transfer of SOX trio enhances the in vitro chondrogenic differentiation of ASCs, and that SOX trio-co-transduced ASCs in fibrin gel promote the healing of osteochondral defects, and arrest the progression of surgically-induced osteoarthritis in a rat model. ASCs isolated from inguinal fat in rats were transduced with SOX trio genes using retrovirus, and further cultured in vitro in pellets for 21 days, then analyzed for gene and protein expression of SOX trio and chondrogenic markers. SOX trio-co-transduced ASCs in fibrin gel were implanted on the osteochondral defect created in the patellar groove of the distal femur, and also injected into the knee joints of rats with surgically-induced osteoarthritis. Rats were sacrificed after 8 weeks, and analyzed grossly and microscopically. After 21 days, ASCs transduced with SOX-5, -6, or -9 had hundreds-fold greater gene expression of each gene compared with the control with the SOX protein expression matching gene expression. SOX trio-co-transduction significantly increased GAG contents as well as type II collagen gene and protein expression. ASCs co-transduced with SOX trio significantly promoted the in vivo cartilage healing in osteochondral defect model, and prevented the progression of degenerative changes in surgically-induced osteoarthritis.

Chromatin accessibility established by Pou5f3, Sox19b and Nanog primes genes for activity during zebrafish genome activation

In many organisms, early embryonic development is driven by maternally provided factors until the controlled onset of transcription during zygotic genome activation. The regulation of chromatin accessibility and its relationship to gene activity during this transition remain poorly understood. Here, we generated chromatin accessibility maps with ATAC-seq from genome activation until the onset of lineage specification. During this period, chromatin accessibility increases at regulatory elements. This increase is independent of RNA polymerase II-mediated transcription, with the exception of the hypertranscribed miR-430 locus. Instead, accessibility often precedes the transcription of associated genes. Loss of the maternal transcription factors Pou5f3, Sox19b, and Nanog, which are known to be required for zebrafish genome activation, results in decreased accessibility at regulatory elements. Importantly, the accessibility of regulatory regions, especially when established by Pou5f3, Sox19b and Nanog, is predictive for future transcription. Our results show that the maternally provided transcription factors Pou5f3, Sox19b, and Nanog open up chromatin and prime genes for activity during zygotic genome activation in zebrafish.

SOXopathies: Growing Family of Developmental Disorders Due to SOX Mutations

The SRY-related (SOX) transcription factor family pivotally contributes to determining cell fate and identity in many lineages. Since the original discovery that SRY deletions cause sex reversal, mutations in half of the 20 human SOX genes have been associated with rare congenital disorders, henceforward called SOXopathies. Mutations are generally de novo, heterozygous, and inactivating, revealing gene haploinsufficiency, but other types, including duplications, have been reported too. Missense variants primarily target the HMG domain, the SOX hallmark that mediates DNA binding and bending, nuclear trafficking, and protein-protein interactions. We here review key clinical and molecular features of SOXopathies and discuss the prospect that the disease family likely involves more SOX genes and larger clinical and genetic spectrums than currently appreciated.

The landscape of pioneer factor activity reveals the mechanisms of chromatin reprogramming and genome activation

Upon fertilization, embryos undergo chromatin reprogramming and genome activation; however, the mechanisms that regulate these processes are poorly understood. Here, we generated a triple mutant for Nanog, Pou5f3, and Sox19b (NPS) in zebrafish and found that NPS pioneer chromatin opening at >50% of active enhancers. NPS regulate acetylation across core histones at enhancers and promoters, and their function in gene activation can be bypassed by recruiting histone acetyltransferase to individual genes. NPS pioneer chromatin opening individually, redundantly, or additively depending on sequence context, and we show that high nucleosome occupancy facilitates NPS pioneering activity. Nucleosome position varies based on the input of different transcription factors (TFs), providing a flexible platform to modulate pioneering activity. Altogether, our results illuminate the sequence of events during genome activation and offer a conceptual framework to understand how pioneer factors interpret the genome and integrate different TF inputs across cell types and developmental transitions.

Global mRNA degradation during lytic gammaherpesvirus infection contributes to establishment of viral latency

During a lytic gammaherpesvirus infection, host gene expression is severely restricted by the global degradation and altered 3' end processing of mRNA. This host shutoff phenotype is orchestrated by the viral SOX protein, yet its functional significance to the viral lifecycle has not been elucidated, in part due to the multifunctional nature of SOX. Using an unbiased mutagenesis screen of the murine gammaherpesvirus 68 (MHV68) SOX homolog, we isolated a single amino acid point mutant that is selectively defective in host shutoff activity. Incorporation of this mutation into MHV68 yielded a virus with significantly reduced capacity for mRNA turnover. Unexpectedly, the MHV68 mutant showed little defect during the acute replication phase in the mouse lung. Instead, the virus exhibited attenuation at later stages of in vivo infections suggestive of defects in both trafficking and latency establishment. Specifically, mice intranasally infected with the host shutoff mutant accumulated to lower levels at 10 days post infection in the lymph nodes, failed to develop splenomegaly, and exhibited reduced viral DNA levels and a lower frequency of latently infected splenocytes. Decreased latency establishment was also observed upon infection via the intraperitoneal route. These results highlight for the first time the importance of global mRNA degradation during a gammaherpesvirus infection and link an exclusively lytic phenomenon with downstream latency establishment.

Yin yang 1 regulates the expression of snail through a distal enhancer

Expression of the Snail gene is required for the epithelial-mesenchymal transitions that accompany mammalian gastrulation, neural crest migration, and organ formation. Pathologic expression of Snail contributes to the migratory capacity of invasive tumors, including melanomas. To investigate the mechanism of Snail up-regulation in human melanoma cells, a conserved enhancer located 3' of the Snail gene was analyzed. An overlapping Ets and yin yang 1 (YY1) consensus sequence, in addition to a SOX consensus sequence, was required for full enhancer activity. Proteins specifically binding these sequences were detected by electrophoretic mobility shift assay. The Ets/YY1 binding activity was purified by DNA-affinity chromatography and identified as YY1. Although ubiquitously expressed, YY1 was bound at the Snail 3' enhancer in vivo in Snail-expressing cells but not in cells that did not express Snail. Knockdown of YY1 in A375 cells led to decreased Snail expression. These results identify a role for YY1 in regulating transcription of Snail in melanoma cells through binding to the Snail 3' enhancer.

Global proteomics analysis of testis and ovary in adult zebrafish (Danio rerio)

The molecular mechanisms controlling sex determination and differentiation in zebrafish (Danio rerio) are largely unknown. A genome-wide analysis may provide comprehensive insights into the processes involved. The mRNA expression in zebrafish gonads has been fairly well studied, but much less data on the corresponding protein expression are available, although the proteins are considered to be more relevant markers of gene function. Because mRNA and protein abundances rarely correlate well, mRNA profiles need to be complemented with the information on protein expression. The work presented here analyzed the proteomes of adult zebrafish gonads by a multidimensional protein identification technology, generating the to-date most populated lists of proteins expressed in mature zebrafish gonads. The acquired proteomics data partially confirmed existing transcriptomics information for several genes, including several novel transcripts. However, disagreements between mRNA and protein abundances were often observed, further stressing the necessity to assess the expression on different levels before drawing conclusions on a certain gene's expression and function. Several gene groups expressed in a sexually dimorphic way in zebrafish gonads were identified. Their potential importance for gonad development and function is discussed. The data gained in the current study provide a basis for further work on elucidating processes occurring during zebrafish development with use of high-throughput proteomics.

The role of Sox genes in lung morphogenesis and cancer

The human lung consists of multiple cell types derived from early embryonic compartments. The morphogenesis of the lung, as well as the injury repair of the adult lung, is tightly controlled by a network of signaling pathways with key transcriptional factors. Lung cancer is the third most cancer-related death in the world, which may be developed due to the failure of regulating the signaling pathways. Sox (sex-determining region Y (Sry) box-containing) family transcriptional factors have emerged as potent modulators in embryonic development, stem cells maintenance, tissue homeostasis, and cancerogenesis in multiple processes. Recent studies demonstrated that the members of the Sox gene family played important roles in the development and maintenance of lung and development of lung cancer. In this context, we summarize our current understanding of the role of Sox family transcriptional factors in the morphogenesis of lung, their oncogenic potential in lung cancer, and their potential impact in the diagnosis, prognosis, and targeted therapy of lung cancer.

Single-molecule imaging correlates decreasing nuclear volume with increasing TF-chromatin associations during zebrafish development

Zygotic genome activation (ZGA), the onset of transcription after initial quiescence, is a major developmental step in many species, which occurs after ten cell divisions in zebrafish embryos. How transcription factor (TF)-chromatin interactions evolve during early development to support ZGA is largely unknown. We establish single molecule tracking in live developing zebrafish embryos using reflected light-sheet microscopy to visualize two fluorescently labeled TF species, mEos2-TBP and mEos2-Sox19b. We further develop a data acquisition and analysis scheme to extract quantitative information on binding kinetics and bound fractions during fast cell cycles. The chromatin-bound fraction of both TFs increases during early development, as expected from a physical model of TF-chromatin interactions including a decreasing nuclear volume and increasing DNA accessibility. For Sox19b, data suggests the increase is mainly due to the shrinking nucleus. Our single molecule approach provides quantitative insight into changes of TF-chromatin associations during the developmental period embracing ZGA.

Transcription factors in SOX family: Potent regulators for cancer initiation and development in the human body

Transcription factors (TFs) have a key role in controlling the gene regulatory network that sustains explicit cell states in humans. However, an uncontrolled regulation of these genes potentially results in a wide range of diseases, including cancer. Genes of the SOX family are indeed crucial as deregulation of SOX family TFs can potentially lead to changes in cell fate as well as irregular cell growth. SOX TFs are a conserved group of transcriptional regulators that mediate DNA binding through a highly conserved high-mobility group (HMG) domain. Accumulating evidence demonstrates that cell fate and differentiation in major developmental processes are controlled by SOX TFs. Besides; numerous reports indicate that both up- and down-regulation of SOX TFs may induce cancer progression. In this review, we discuss the involvement of key TFs of SOX family in human cancers.

Specification of arterial, venous, and lymphatic endothelial cells during embryonic development

The groundbreaking discovery about arterial and venous expression of ephrinB2 and EphB4, respectively, in early embryonic development has led to a new paradigm for vascular research, providing compelling evidence that arterial and venous endothelial cells are established by genetic mechanisms before circulation begins. For arterial specification, vascular endothelial growth factor (VEGF) induces expression of Notch signaling genes, including Notch1 and its ligand, Delta-like 4 (Dll4), and Foxc1 and Foxc2 transcription factors directly regulate Dll4 expression. Upon activation of Notch signaling, the Notch downstream genes, Hey1/2 in mice or gridlock in zebrafish, further promote arterial differentiation. On the other hand, the orphan nuclear receptor COUP-TFII is a determinant factor for venous specification by inhibiting expression of arterial specific genes, including Nrp1 and Notch. After arterial and venous endothelial cells differentiate, a subpopulation of venous endothelial cells is thought to become competent to acquire lymphatic endothelial cell fate by progressively expressing the transcription factors Sox18 and Prox1 to differentiate into lymphatic endothelial cells. Therefore, it has now evident that arterial-venous cell fate determination and subsequent lymphatic development are regulated by the multi-step regulatory system associated with the key signaling pathways and transcription factors. Furthermore, new signaling molecules as additional regulators in these processes have recently been identified. As the mechanistic basis for a link between signaling pathways and transcriptional networks in arterial, venous and lymphatic endothelial cells begins to be uncovered, it is now time to summarize the literature on this exciting topic and provide perspectives for future research in the field.

Molecular mechanisms of Sox transcription factors during the development of liver, bile duct, and pancreas

The liver and pancreas are the prime digestive and metabolic organs in the body. After emerging from the neighboring domains of the foregut endoderm, they turn on distinct differentiation and morphogenesis programs that are regulated by hierarchies of transcription factors. Members of SOX family of transcription factors are expressed in the liver and pancreas throughout development and act upstream of other organ-specific transcription factors. They play key roles in maintaining stem cells and progenitors. They are also master regulators of cell fate determination and tissue morphogenesis. In this review, we summarize the current understanding of SOX transcription factors in mediating liver and pancreas development. We discuss their contribution to adult organ function, homeostasis and injury responses. We also speculate how the knowledge of SOX transcription factors can be applied to improve therapies for liver diseases and diabetes.

Sox21 regulates the progression of neuronal differentiation in a dose-dependent manner

Members of the SoxB transcription factor family play critical roles in the regulation of neurogenesis. The SoxB1 proteins are required for the induction and maintenance of a proliferating neural progenitor population in numerous vertebrates, however the role of the SoxB2 protein, Sox21, is less clear due to conflicting results. To clarify the role of Sox21 in neurogenesis, we examined its function in the Xenopus neural plate. Here we report that misexpression of Sox21 expands the neural progenitor domain, and represses neuron formation by binding to Neurogenin (Ngn2) and blocking its function. Conversely, we found that Sox21 is also required for neuron formation, as cells lacking Sox21 undergo cell death and thus are unable to differentiate. Together our data indicate that Sox21 plays more than one role in neurogenesis, where a threshold level is required for cell viability and normal differentiation of neurons, but a higher concentration of Sox21 inhibits neuron formation and instead promotes progenitor maintenance.

The role of SOX proteins in normal pituitary development

Pituitary development is a complex process that depends on the co-ordinated spatial and temporal expression of transcription factors and signalling molecules that culminates in the formation of a complex organ that secretes six hormones from five different cell types. Given the fact that all distinct hormone producing cells arise from a common ectodermal primordium, the patterning, architecture and plasticity of the gland is impressive. Among the transcription factors involved in the early steps of pituitary organogenesis are SOX2 and SOX3, members of the SOX family that are emerging as key players in many developmental processes. Studies in vitro and in vivo in transgenic animal models have helped to elucidate their expression patterns and roles in the developing hypothalamo-pituitary region. It has been demonstrated that they may be involved in pituitary development either directly, through shaping of Rathke's pouch, or indirectly affecting signalling from the diencephalon. Their role has been further underlined by the pleiotropic effects of their mutations in humans that range from isolated hormone deficiencies to panhypopituitarism and developmental abnormalities affecting many organ systems. However, the exact mechanism of action of SOX proteins, their downstream targets and their interplay within the extensive network that regulates pituitary development is still the subject of a growing number of studies. The elucidation of their role is crucial for the understanding of a number of processes that range from developmental mechanisms to disease phenotypes and tumorigenesis.

A novel functional role of iduronate-2-sulfatase in zebrafish early development

Sulfated glycosaminoglycan chains of extracellular matrix and cell membrane-tethered proteoglycans exert specific cellular functions by interacting with a broad spectrum of morphogens and growth factors. In humans, a congenital impaired catabolism of sulfated glycosaminoglycans is associated with severe metabolic disorders. Here, we report on the identification and characterization of a zebrafish iduronate sulfatase orthologue. By knocking down its function with antisense morpholino oligos, we demonstrate that iduronate sulfatase plays a critical role during early vertebrate development and its downregulation may be responsible for severe developmental defects, including a misshapen trunk and abnormal craniofacial cartilages. We show that the altered cartilage patterning is mediated by depauperation of sox10-expressing neural crest cell precursors. Through the application of a transactivation reporter assay, we also provide a molecular proof that increased TGFbeta (Transforming Growth Factor beta) signalling is tightly associated with downregulation of iduronate sulfatase function. Our results provide an insight into the early biological impairments underlying the Hunter syndrome and suggest the use of zebrafish as a novel tool to better understand lysosomal storage disorder pathogenesis.

c-Lysozyme from Senegalese sole (Solea senegalensis): cDNA cloning and expression pattern

Lysozymes are key molecules of innate immunity and proved high bactericidal activity in fish, thus becoming attractive as tools for enhancing fish defences. In this study, a full-length c-type lysozyme cDNA from Senegalese sole (Solea senegalensis) has been cloned and characterized. The cDNA sequence was inferred from two overlapping fragments obtained by RACE-PCR and consisting on 631bp coding for 143 aminoacids. Catalytic and other conserved residues required for lysozyme activity were identified. Pair wise alignments showed the higher identities with c-type lysozyme from other flatfish. Expression patterns under various conditions showed a basal level and a clear upregulation mostly in hematopoietic organs after stimulation with LPS or infection with Photobacterium damselae. This study represents a first step on the genetics and function of the c-lysozyme of Senegalese sole, though disclosing g-DNA structure, allelic variability and antibacterial activity must be requirements prior its immunological properties might have biotechnological applications.

Role of the mar-sox-rob regulon in regulating outer membrane porin expression

Multiple factors control the expression of the outer membrane porins OmpF and OmpC in Escherichia coli. In this work, we investigated the role of the mar-sox-rob regulon in regulating outer membrane porin expression in response to salicylate. We provide both genetic and physiological evidence that MarA and Rob can independently activate micF transcription in response to salicylate, leading to reduced OmpF expression. MarA was also found to repress OmpF expression through a MicF-independent pathway. In the case of OmpC, we found that its transcription was moderately increased in response to salicylate. However, this increase was independent of MarA and Rob. Finally, we found that the reduction in OmpF expression in a tolC mutant is due primarily to Rob. Collectively, this work further clarifies the coordinated role of MarA and Rob in regulating the expression of the outer membrane porins.