SoxE Factors Function Equivalently during Neural Crest and Inner Ear Development and Their Activity Is Regulated by SUMOylation

SUMO-dependent transcriptional repression by Sox2 inhibits the proliferation of neural stem cells

Sox2 is known for its roles in maintaining the stem cell state of embryonic stem cells and neural stem cells. In particular, it has been shown to slow the proliferation of these cell types. It is also known for its effects as an activating transcription factor. Despite this, analysis of published studies shows that it represses as many genes as it activates. Here, we identify a new set of target genes that Sox2 represses in neural stem cells. These genes are associated with centrosomes, centromeres and other aspects of cell cycle control. In addition, we show that SUMOylation of Sox2 is necessary for the repression of these genes and for its repressive effects on cell proliferation. Together, these data suggest that SUMO-dependent repression of this group of target genes is responsible for the role of Sox2 in regulating the proliferation of neural stem cells.

Clinical Significance of SOX10 Expression in Human Pathology

The embryonic development of neural crest cells and subsequent tissue differentiation are intricately regulated by specific transcription factors. Among these, SOX10, a member of the SOX gene family, stands out. Located on chromosome 22q13, the SOX10 gene encodes a transcription factor crucial for the differentiation, migration, and maintenance of tissues derived from neural crest cells. It plays a pivotal role in developing various tissues, including the central and peripheral nervous systems, melanocytes, chondrocytes, and odontoblasts. Mutations in SOX10 have been associated with congenital disorders such as Waardenburg-Shah Syndrome, PCWH syndrome, and Kallman syndrome, underscoring its clinical significance. Furthermore, SOX10 is implicated in neural and neuroectodermal tumors, such as melanoma, malignant peripheral nerve sheath tumors (MPNSTs), and schwannomas, influencing processes like proliferation, migration, and differentiation. In mesenchymal tumors, SOX10 expression serves as a valuable marker for distinguishing between different tumor types. Additionally, SOX10 has been identified in various epithelial neoplasms, including breast, ovarian, salivary gland, nasopharyngeal, and bladder cancers, presenting itself as a potential diagnostic and prognostic marker. However, despite these associations, further research is imperative to elucidate its precise role in these malignancies.

Phenotype-genotype relationships in Xenopus sox9 crispants provide insights into campomelic dysplasia and vertebrate jaw evolution

Since CRISPR-based genome editing technology works effectively in the diploid frog Xenopus tropicalis, a growing number of studies have successfully modeled human genetic diseases in this species. However, most of their targets were limited to non-syndromic diseases that exhibit abnormalities in a small fraction of tissues or organs in the body. This is likely because of the complexity of interpreting the phenotypic variations resulting from somatic mosaic mutations generated in the founder animals (crispants). In this study, we attempted to model the syndromic disease campomelic dysplasia (CD) by generating sox9 crispants in X. tropicalis. The resulting crispants failed to form neural crest cells at neurula stages and exhibited various combinations of jaw, gill, ear, heart, and gut defects at tadpole stages, recapitulating part of the syndromic phenotype of CD patients. Genotyping of the crispants with a variety of allelic series of mutations suggested that the heart and gut defects depend primarily on frame-shift mutations expected to be null, whereas the jaw, gill, and ear defects could be induced not only by such mutations but also by in-frame deletion mutations expected to delete part of the jawed vertebrate-specific domain from the encoded Sox9 protein. These results demonstrate that Xenopus crispants are useful for investigating the phenotype-genotype relationships behind syndromic diseases and examining the tissue-specific role of each functional domain within a single protein, providing novel insights into vertebrate jaw evolution.

Sox9 Inhibits Cochlear Hair Cell Fate by Upregulating Hey1 and HeyL Antagonists of Atoh1

It is widely accepted that cell fate determination in the cochlea is tightly controlled by different transcription factors (TFs) that remain to be fully defined. Here, we show that Sox9, initially expressed in the entire sensory epithelium of the cochlea, progressively disappears from differentiating hair cells (HCs) and is finally restricted to supporting cells (SCs). By performing ex vivo electroporation of E13.5-E14.5 cochleae, we demonstrate that maintenance of Sox9 expression in the progenitors committed to HC fate blocks their differentiation, even if co-expressed with Atoh1, a transcription factor necessary and sufficient to form HC. Sox9 inhibits Atoh1 transcriptional activity by upregulating Hey1 and HeyL antagonists, and genetic ablation of these genes induces extra HCs along the cochlea. Although Sox9 suppression from sensory progenitors ex vivo leads to a modest increase in the number of HCs, it is not sufficient in vivo to induce supernumerary HC production in an inducible Sox9 knockout model. Taken together, these data show that Sox9 is downregulated from nascent HCs to allow the unfolding of their differentiation program. This may be critical for future strategies to promote fully mature HC formation in regeneration approaches.

SUMO control of nervous system development

In the last decades, the post-translational modification system by covalent attachment of the SUMO polypeptide to proteins has emerged as an essential mechanism controlling virtually all the physiological processes in the eukaryotic cell. This includes vertebrate development. In the nervous system, SUMO plays crucial roles in synapse establishment and it has also been linked to a variety of neurodegenerative diseases. However, to date, the involvement of the modification of specific targets in key aspects of nervous system development, like patterning and differentiation, has remained largely elusive. A number of recent works confirm the participation of target-specific SUMO modification in critical aspects of nervous system development. Here, we review pioneering and new findings demonstrating the essential role SUMO plays in neurogenesis and other facets of neurodevelopment, which will help to precisely understand the variety of mechanisms SUMO utilizes to control most fundamental processes in the cell.

Stemness Activity Underlying Whole Brain Regeneration in a Basal Chordate

Understanding how neurons regenerate following injury remains a central challenge in regenerative medicine. Adult mammals have a very limited ability to regenerate new neurons in the central nervous system (CNS). In contrast, the basal chordate Polycarpa mytiligera can regenerate its entire CNS within seven days of complete removal. Transcriptome sequencing, cellular labeling, and proliferation in vivo essays revealed that CNS regeneration is mediated by a newly formed neural progeny and the activation of neurodevelopmental pathways that are associated with enhanced stem-cell activity. Analyzing the expression of 239 activated pathways enabled a quantitative understanding of gene-set enrichment patterns at key regeneration stages. The molecular and cellular mechanisms controlling the regenerative ability that this study reveals can be used to develop innovative approaches to enhancing neurogenesis in closely-related chordate species, including humans.

SOX9 and SOX10 control fluid homeostasis in the inner ear for hearing through independent and cooperative mechanisms

The in vivo mechanisms underlying dominant syndromes caused by mutations in SRY-Box Transcription Factor 9 (SOX9) and SOX10 (SOXE) transcription factors, when they either are expressed alone or are coexpressed, are ill-defined. We created a mouse model for the campomelic dysplasia SOX9Y440X mutation, which truncates the transactivation domain but leaves DNA binding and dimerization intact. Here, we find that SOX9Y440X causes deafness via distinct mechanisms in the endolymphatic sac (ES)/duct and cochlea. By contrast, conditional heterozygous Sox9-null mice are normal. During the ES development of Sox9Y440X/+ heterozygotes, Sox10 and genes important for ionic homeostasis are down-regulated, and there is developmental persistence of progenitors, resulting in fewer mature cells. Sox10 heterozygous null mutants also display persistence of ES/duct progenitors. By contrast, SOX10 retains its expression in the early Sox9Y440X/+ mutant cochlea. Later, in the postnatal stria vascularis, dominant interference by SOX9Y440X is implicated in impairing the normal cooperation of SOX9 and SOX10 in repressing the expression of the water channel Aquaporin 3, thereby contributing to endolymphatic hydrops. Our study shows that for a functioning endolymphatic system in the inner ear, SOX9 regulates Sox10, and depending on the cell type and target gene, it works either independently of or cooperatively with SOX10. SOX9Y440X can interfere with the activity of both SOXE factors, exerting effects that can be classified as haploinsufficient/hypomorphic or dominant negative depending on the cell/gene context. This model of disruption of transcription factor partnerships may be applicable to congenital deafness, which affects ∼0.3% of newborns, and other syndromic disorders.

SOX9 in organogenesis: shared and unique transcriptional functions

The transcription factor SOX9 is essential for the development of multiple organs including bone, testis, heart, lung, pancreas, intestine and nervous system. Mutations in the human SOX9 gene led to campomelic dysplasia, a haploinsufficiency disorder with several skeletal malformations frequently accompanied by 46, XY sex reversal. The mechanisms underlying the diverse SOX9 functions during organ development including its post-translational modifications, the availability of binding partners, and tissue-specific accessibility to target gene chromatin. Here we summarize the expression, activities, and downstream target genes of SOX9 in molecular genetic pathways essential for organ development, maintenance, and function. We also provide an insight into understanding the mechanisms that regulate the versatile roles of SOX9 in different organs.

Sox8 remodels the cranial ectoderm to generate the ear

The vertebrate inner ear arises from a pool of progenitors with the potential to contribute to all the sense organs and cranial ganglia in the head. Here, we explore the molecular mechanisms that control ear specification from these precursors. Using a multiomics approach combined with loss-of-function experiments, we identify a core transcriptional circuit that imparts ear identity, along with a genome-wide characterization of noncoding elements that integrate this information. This analysis places the transcription factor Sox8 at the top of the ear determination network. Introducing Sox8 into the cranial ectoderm not only converts non-ear cells into ear progenitors but also activates the cellular programs for ear morphogenesis and neurogenesis. Thus, Sox8 has the unique ability to remodel transcriptional networks in the cranial ectoderm toward ear identity.

Influence of Sox protein SUMOylation on neural development and regeneration

SRY-related HMG-box (Sox) transcription factors are known to regulate central nervous system development and are involved in several neurological diseases. Post-translational modification of Sox proteins is known to alter their functions in the central nervous system. Among the different types of post-translational modification, small ubiquitin-like modifier (SUMO) modification of Sox proteins has been shown to modify their transcriptional activity. Here, we review the mechanisms of three Sox proteins in neuronal development and disease, along with their transcriptional changes under SUMOylation. Across three species, lysine is the conserved residue for SUMOylation. In Drosophila, SUMOylation of SoxN plays a repressive role in transcriptional activity, which impairs central nervous system development. However, deSUMOylation of SoxE and Sox11 plays neuroprotective roles, which promote neural crest precursor formation in Xenopus and retinal ganglion cell differentiation as well as axon regeneration in the rodent. We further discuss a potential translational therapy by SUMO site modification using AAV gene transduction and Clustered regularly interspaced short palindromic repeats-Cas9 technology. Understanding the underlying mechanisms of Sox SUMOylation, especially in the rodent system, may provide a therapeutic strategy to address issues associated with neuronal development and neurodegeneration.

Signal pathways of melanoma and targeted therapy

Melanoma is the most lethal skin cancer that originates from the malignant transformation of melanocytes. Although melanoma has long been regarded as a cancerous malignancy with few therapeutic options, increased biological understanding and unprecedented innovations in therapies targeting mutated driver genes and immune checkpoints have substantially improved the prognosis of patients. However, the low response rate and inevitable occurrence of resistance to currently available targeted therapies have posed the obstacle in the path of melanoma management to obtain further amelioration. Therefore, it is necessary to understand the mechanisms underlying melanoma pathogenesis more comprehensively, which might lead to more substantial progress in therapeutic approaches and expand clinical options for melanoma therapy. In this review, we firstly make a brief introduction to melanoma epidemiology, clinical subtypes, risk factors, and current therapies. Then, the signal pathways orchestrating melanoma pathogenesis, including genetic mutations, key transcriptional regulators, epigenetic dysregulations, metabolic reprogramming, crucial metastasis-related signals, tumor-promoting inflammatory pathways, and pro-angiogenic factors, have been systemically reviewed and discussed. Subsequently, we outline current progresses in therapies targeting mutated driver genes and immune checkpoints, as well as the mechanisms underlying the treatment resistance. Finally, the prospects and challenges in the development of melanoma therapy, especially immunotherapy and related ongoing clinical trials, are summarized and discussed.

Contribution of sox9b to pigment cell formation in medaka fish

SoxE-type transcription factors, Sox10 and Sox9, are key regulators of the development of neural crest cells. Sox10 specifies pigment cell, glial, and neuronal lineages, whereas Sox9 is reportedly closely associated with skeletogenic lineages in the head, but its involvement in pigment cell formation has not been investigated genetically. Thus, it is not fully understood whether or how distinctly these genes as well as their paralogs in teleosts are subfunctionalized. We have previously shown using the medaka fish Oryzias latipes that pigment cell formation is severely affected by the loss of sox10a, yet unaffected by the loss of sox10b. Here we aimed to determine whether Sox9 is involved in the specification of pigment cell lineage. The sox9b homozygous mutation did not affect pigment cell formation, despite lethality at the early larval stages. By using sox10a, sox10b, and sox9b mutations, compound mutants were established for the sox9b and sox10 genes and pigment cell phenotypes were analyzed. Simultaneous loss of sox9b and sox10a resulted in the complete absence of melanophores and xanthophores from hatchlings and severely defective iridophore formation, as has been previously shown for sox10a^-/- ; sox10b^-/- double mutants, indicating that Sox9b as well as Sox10b functions redundantly with Sox10a in pigment cell development. Notably, leucophores were present in sox9b^-/- ; sox10a^-/- and sox10a^-/- ; sox10b^-/- double mutants, but their numbers were significantly reduced in the sox9b^-/- ; sox10a^-/- mutants. These findings highlight that Sox9b is involved in pigment cell formation, and plays a more critical role in leucophore development than Sox10b.

SOX10: 20 years of phenotypic plurality and current understanding of its developmental function

SOX10 belongs to a family of 20 SRY (sex-determining region Y)-related high mobility group box-containing (SOX) proteins, most of which contribute to cell type specification and differentiation of various lineages. The first clue that SOX10 is essential for development, especially in the neural crest, came with the discovery that heterozygous mutations occurring within and around SOX10 cause Waardenburg syndrome type 4. Since then, heterozygous mutations have been reported in Waardenburg syndrome type 2 (Waardenburg syndrome type without Hirschsprung disease), PCWH or PCW (peripheral demyelinating neuropathy, central dysmyelination, Waardenburg syndrome, with or without Hirschsprung disease), intestinal manifestations beyond Hirschsprung (ie, chronic intestinal pseudo-obstruction), Kallmann syndrome and cancer. All of these diseases are consistent with the regulatory role of SOX10 in various neural crest derivatives (melanocytes, the enteric nervous system, Schwann cells and olfactory ensheathing cells) and extraneural crest tissues (inner ear, oligodendrocytes). The recent evolution of medical practice in constitutional genetics has led to the identification of SOX10 variants in atypical contexts, such as isolated hearing loss or neurodevelopmental disorders, making them more difficult to classify in the absence of both a typical phenotype and specific expertise. Here, we report novel mutations and review those that have already been published and their functional consequences, along with current understanding of SOX10 function in the affected cell types identified through in vivo and in vitro models. We also discuss research options to increase our understanding of the origin of the observed phenotypic variability and improve the diagnosis and medical care of affected patients.

SUMOylation Potentiates ZIC Protein Activity to Influence Murine Neural Crest Cell Specification

The mechanisms of neural crest cell induction and specification are highly conserved among vertebrate model organisms, but how similar these mechanisms are in mammalian neural crest cell formation remains open to question. The zinc finger of the cerebellum 1 (ZIC1) transcription factor is considered a core component of the vertebrate gene regulatory network that specifies neural crest fate at the neural plate border. In mouse embryos, however, Zic1 mutation does not cause neural crest defects. Instead, we and others have shown that murine Zic2 and Zic5 mutate to give a neural crest phenotype. Here, we extend this knowledge by demonstrating that murine Zic3 is also required for, and co-operates with, Zic2 and Zic5 during mammalian neural crest specification. At the murine neural plate border (a region of high canonical WNT activity) ZIC2, ZIC3, and ZIC5 function as transcription factors to jointly activate the Foxd3 specifier gene. This function is promoted by SUMOylation of the ZIC proteins at a conserved lysine immediately N-terminal of the ZIC zinc finger domain. In contrast, in the lateral regions of the neurectoderm (a region of low canonical WNT activity) basal ZIC proteins act as co-repressors of WNT/TCF-mediated transcription. Our work provides a mechanism by which mammalian neural crest specification is restricted to the neural plate border. Furthermore, given that WNT signaling and SUMOylation are also features of non-mammalian neural crest specification, it suggests that mammalian neural crest induction shares broad conservation, but altered molecular detail, with chicken, zebrafish, and Xenopus neural crest induction.

Using the lineage determinants Olig2 and Sox10 to explore transcriptional regulation of oligodendrocyte development

The transcription factors Olig2 and Sox10 jointly define oligodendroglial identity. Because of their continuous presence during development and in the differentiated state they shape the oligodendroglial regulatory network at all times. In this review, we exploit their eminent role and omnipresence to elaborate the central principles that organize the gene regulatory network in oligodendrocytes in such a way that it preserves its identity, but at the same time allows defined and stimulus-dependent changes that result in an ordered lineage progression, differentiation, and myelination. For this purpose, we outline the multiple functional and physical interactions and intricate cross-regulatory relationships with other transcription factors, such as Hes5, Id, and SoxD proteins, in oligodendrocyte precursors and Tcf7l2, Sip1, Nkx2.2, Zfp24, and Myrf during differentiation and myelination, and interpret them in the context of the regulatory network.

Wrestling and Wrapping: A Perspective on SUMO Proteins in Schwann Cells

Schwann cell development and peripheral nerve myelination are finely orchestrated multistep processes; some of the underlying mechanisms are well described and others remain unknown. Many posttranslational modifications (PTMs) like phosphorylation and ubiquitination have been reported to play a role during the normal development of the peripheral nervous system (PNS) and in demyelinating neuropathies. However, a relatively novel PTM, SUMOylation, has not been studied in these contexts. SUMOylation involves the covalent attachment of one or more small ubiquitin-like modifier (SUMO) proteins to a substrate, which affects the function, cellular localization, and further PTMs of the conjugated protein. SUMOylation also regulates other proteins indirectly by facilitating non-covalent protein–protein interaction via SUMO interaction motifs (SIM). This pathway has important consequences on diverse cellular processes, and dysregulation of this pathway has been reported in several diseases including neurological and degenerative conditions. In this article, we revise the scarce literature on SUMOylation in Schwann cells and the PNS, we propose putative substrate proteins, and we speculate on potential mechanisms underlying the possible involvement of this PTM in peripheral myelination and neuropathies.

SOX Transcription Factors as Important Regulators of Neuronal and Glial Differentiation During Nervous System Development and Adult Neurogenesis

The SOX proteins belong to the superfamily of transcription factors (TFs) that display properties of both classical TFs and architectural components of chromatin. Since the cloning of the Sox/SOX genes, remarkable progress has been made in illuminating their roles as key players in the regulation of multiple developmental and physiological processes. SOX TFs govern diverse cellular processes during development, such as maintaining the pluripotency of stem cells, cell proliferation, cell fate decisions/germ layer formation as well as terminal cell differentiation into tissues and organs. However, their roles are not limited to development since SOX proteins influence survival, regeneration, cell death and control homeostasis in adult tissues. This review summarized current knowledge of the roles of SOX proteins in control of central nervous system development. Some SOX TFs suspend neural progenitors in proliferative, stem-like state and prevent their differentiation. SOX proteins function as pioneer factors that occupy silenced target genes and keep them in a poised state for activation at subsequent stages of differentiation. At appropriate stage of development, SOX members that maintain stemness are down-regulated in cells that are competent to differentiate, while other SOX members take over their functions and govern the process of differentiation. Distinct SOX members determine down-stream processes of neuronal and glial differentiation. Thus, sequentially acting SOX TFs orchestrate neural lineage development defining neuronal and glial phenotypes. In line with their crucial roles in the nervous system development, deregulation of specific SOX proteins activities is associated with neurodevelopmental disorders (NDDs). The overview of the current knowledge about the link between SOX gene variants and NDDs is presented. We outline the roles of SOX TFs in adult neurogenesis and brain homeostasis and discuss whether impaired adult neurogenesis, detected in neurodegenerative diseases, could be associated with deregulation of SOX proteins activities. We present the current data regarding the interaction between SOX proteins and signaling pathways and microRNAs that play roles in nervous system development. Finally, future research directions that will improve the knowledge about distinct and various roles of SOX TFs in health and diseases are presented and discussed.

WNT responsive SUMOylation of ZIC5 promotes murine neural crest cell development via multiple effects on transcription

Zinc finger of the cerebellum (Zic) proteins act as classical transcription factors to promote transcription of the Foxd3 gene during neural crest cell specification. Additionally, they can act as co-factors that bind TCF molecules to repress WNT/β-catenin-dependent transcription without contacting DNA. Here, we show ZIC activity at the neural plate border is influenced by WNT-dependent SUMOylation. In a high WNT environment, a lysine within the highly conserved ZF-NC domain of ZIC5 is SUMOylated, which decreases formation of the TCF/ZIC co-repressor complex and shifts the balance towards transcription factor function. The modification is critical in vivo, as a ZIC5 SUMO-incompetent mouse strain exhibits neural crest specification defects. This work reveals the function of the ZIC ZF-NC domain, provides in vivo validation of target protein SUMOylation, and demonstrates that WNT/β-catenin signaling directs transcription at non-TCF DNA binding sites. Furthermore, it can explain how WNT signals convert a broad domain of Zic ectodermal expression into a restricted domain of neural crest cell specification.

Sorting Sox: Diverse Roles for Sox Transcription Factors During Neural Crest and Craniofacial Development

Sox transcription factors play many diverse roles during development, including regulating stem cell states, directing differentiation, and influencing the local chromatin landscape. Of the twenty vertebrate Sox factors, several play critical roles in the development the neural crest, a key vertebrate innovation, and the subsequent formation of neural crest-derived structures, including the craniofacial complex. Herein, we review the specific roles for individual Sox factors during neural crest cell formation and discuss how some factors may have been essential for the evolution of the neural crest. Additionally, we describe how Sox factors direct neural crest cell differentiation into diverse lineages such as melanocytes, glia, and cartilage and detail their involvement in the development of specific craniofacial structures. Finally, we highlight several SOXopathies associated with craniofacial phenotypes.

KEAP1 Mutations Drive Tumorigenesis by Suppressing SOX9 Ubiquitination and Degradation

The transcription factor SOX9 is frequently amplified in diverse advanced-stage human tumors. Its stability has been shown to be tightly controlled by ubiquitination-dependent proteasome degradation. However, the exact underlying molecular mechanisms remain unclear. This work reports that SOX9 protein abundance is regulated by the Cullin 3-based ubiquitin ligase KEAP1 via proteasome-mediated degradation. Loss-of-function mutations in KEAP1 compromise polyubiquitination-mediated SOX9 degradation, leading to increased protein levels, which facilitate tumorigenesis. Moreover, the loss of critical ubiquitination residues in SOX9, by either a SOX9 (ΔK2) truncation or K249R mutation, leads to elevated protein stability. Furthermore, it is shown that the KEAP1/SOX9 interaction is modulated by CKIγ-mediated phosphorylation. Importantly, it is demonstrated that DNA damage drugs, topoisomerase inhibitors, can trigger CKI activation to restore the KEAP1/SOX9 interaction and its consequent degradation. Collectively, herein the findings uncover a novel molecular mechanism through which SOX9 protein stability is negatively regulated by KEAP1 to control tumorigenesis. Thus, these results suggest that mitigating SOX9 resistance to KEAP1-mediated degradation can represent a novel therapeutic strategy for cancers with KEAP1 mutations.

The transcription factors SF-1 and SOX8 cooperate to upregulate Cx43 expression in mouse TM4 sertoli cells

Gap junctions made by connexins within the adult testis are essential for communication between Sertoli cells and for spermatogenesis. Sertoli cells play an important role in supporting germ cells differentiation and maturation into spermatozoa. Connexin43 (Cx43) is the most abundant and important connexin of the testis. We have shown previously that the expression of Cx43 is being regulated by SOX and AP-1 transcription factors in Sertoli cells. However, additional regulatory elements being able to recruit orphan nuclear receptors may be involved. Since SOX and SF-1 transcription factors have been shown to cooperate to regulate gene expression in Sertoli cells, we wondered if such mechanism could be involved in the activation of Cx43 expression. Thus, the activity of the Cx43 promoter was measured by co-transfections of luciferase reporter plasmid constructs with different expression vectors for transcription factors in the TM4 Sertoli cell line. The recruitment of SF-1 to the proximal region of the Cx43 promoter was evaluated by chromatin immunoprecipitation. Our results indicate that SOX8 and SF-1, as well as SOX9 and Nur77, cooperate to activate the expression of Cx43 and that SF-1 is being recruited to the −132 to −26 bp region of the Cx43 promoter. These results allow us to have a better understanding of the mechanisms regulating Cx43 expression and could explain some disturbances in communication between Sertoli cells responsible for impaired fertility.

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SF-1 and SOX8 cooperate to activate Cx43 expression in TM4 Sertoli cells.

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SF-1 is being recruited to the proximal region of the Cx43 promoter.

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LRH-1 and Nur77 also cooperate with SOX factors to activate Cx43 expression.

Neurogenesis From Neural Crest Cells: Molecular Mechanisms in the Formation of Cranial Nerves and Ganglia

The neural crest (NC) is a transient multipotent cell population that originates in the dorsal neural tube. Cells of the NC are highly migratory, as they travel considerable distances through the body to reach their final sites. Derivatives of the NC are neurons and glia of the peripheral nervous system (PNS) and the enteric nervous system as well as non-neural cells. Different signaling pathways triggered by Bone Morphogenetic Proteins (BMPs), Fibroblast Growth Factors (FGFs), Wnt proteins, Notch ligands, retinoic acid (RA), and Receptor Tyrosine Kinases (RTKs) participate in the processes of induction, specification, cell migration and neural differentiation of the NC. A specific set of signaling pathways and transcription factors are initially expressed in the neural plate border and then in the NC cell precursors to the formation of cranial nerves. The molecular mechanisms of control during embryonic development have been gradually elucidated, pointing to an important role of transcriptional regulators when neural differentiation occurs. However, some of these proteins have an important participation in malformations of the cranial portion and their mutation results in aberrant neurogenesis. This review aims to give an overview of the role of cell signaling and of the function of transcription factors involved in the specification of ganglia precursors and neurogenesis to form the NC-derived cranial nerves during organogenesis.

SUMOylation controls the neurodevelopmental function of the transcription factor Zbtb20

SUMOylation is a dynamic post-translational protein modification that primarily takes place in cell nuclei, where it plays a key role in multiple DNA-related processes. In neurons, the SUMOylation-dependent control of a subset of neuronal transcription factors is known to regulate various aspects of nerve cell differentiation, development, and function. In an unbiased screen for endogenous SUMOylation targets in the developing mouse brain, based on a His₆ -HA-SUMO1 knock-in mouse line, we previously identified the transcription factor Zinc finger and BTB domain-containing 20 (Zbtb20) as a new SUMO1-conjugate. We show here that the three key SUMO paralogues SUMO1, SUMO2, and SUMO3 can all be conjugated to Zbtb20 in vitro in HEK293FT cells, and we confirm the SUMOylation of Zbtb20 in vivo in mouse brain. Using primary hippocampal neurons from wild-type and Zbtb20 knock-out (KO) mice as a model system, we then demonstrate that the expression of Zbtb20 is required for proper nerve cell development and neurite growth and branching. Furthermore, we show that the SUMOylation of Zbtb20 is essential for its function in this context, and provide evidence indicating that SUMOylation affects the Zbtb20-dependent transcriptional profile of neurons. Our data highlight the role of SUMOylation in the regulation of neuronal transcription factors that determine nerve cell development, and they demonstrate that key functions of the transcription factor Zbtb20 in neuronal development and neurite growth are under obligatory SUMOylation control.

Generation of a Quantitative Luciferase Reporter for Sox9 SUMOylation

Sox9 is a master transcription factor for chondrogenesis, which is essential for chondrocyte proliferation, differentiation, and maintenance. Sox9 activity is regulated by multiple layers, including post-translational modifications, such as SUMOylation. A detection method for visualizing the SUMOylation in live cells is required to fully understand the role of Sox9 SUMOylation. In this study, we generated a quantitative reporter for Sox9 SUMOylation that is based on the NanoBiT system. The simultaneous expression of Sox9 and SUMO1 constructs that are conjugated with NanoBiT fragments in HEK293T cells induced luciferase activity in SUMOylation target residue of Sox9-dependent manner. Furthermore, the reporter signal could be detected from both cell lysates and live cells. The signal level of our reporter responded to the co-expression of SUMOylation or deSUMOylation enzymes by several fold, showing dynamic potency of the reporter. The reporter was active in multiple cell types, including ATDC5 cells, which have chondrogenic potential. Finally, using this reporter, we revealed a extracellular signal conditions that can increase the amount of SUMOylated Sox9. In summary, we generated a novel reporter that was capable of quantitatively visualizing the Sox9-SUMOylation level in live cells. This reporter will be useful for understanding the dynamism of Sox9 regulation during chondrogenesis.

Acquisition of multipotent and migratory neural crest cells in vertebrate evolution

The emergence of multipotent and migratory neural crest (NC) cells defines a key evolutionary transition from invertebrates to vertebrates. Studies in vertebrates have identified a complex gene regulatory network that governs sequential stages of NC ontogeny. Comparative analysis has revealed extensive conservation of the overall architecture of the NC gene regulatory network between jawless and jawed vertebrates. Among invertebrates, urochordates express putative NC gene homologs in the neural plate border region, but these NC-like cells do not have migratory capacity, whereas cephalochordates contain no NC cells but its genome contains most homologs of vertebrate NC genes. Whether the absence of migratory NC cells in invertebrates is due to differences in enhancer elements or an intrinsic limitation in potency remains unclear. We provide a brief overview of mechanisms that might explain how ancestral NC-like cells acquired the multipotency and migratory capacity seen in vertebrates.

Transcriptional control of myelination and remyelination

Myelination is an evolutionary recent differentiation program that has been independently acquired in vertebrates by Schwann cells in the peripheral nervous system and oligodendrocytes in the central nervous system. Therefore, it is not surprising that regulating transcription factors differ substantially between both cell types. However, overall principles are similar as transcriptional control in Schwann cells and oligodendrocytes combines lineage determining and stage-specific factors in complex regulatory networks. Myelination does not only occur during development, but also as remyelination in the adult. In line with the different conditions during developmental myelination and remyelination and the distinctive properties of Schwann cells and oligodendrocytes, transcriptional regulation of remyelination exhibits unique features and differs between the two cell types. This review gives an overview of the current state in the field.

sox9b is required in cardiomyocytes for cardiac morphogenesis and function

The high mobility group transcription factor SOX9 is expressed in stem cells, progenitor cells, and differentiated cell-types in developing and mature organs. Exposure to a variety of toxicants including dioxin, di(2-ethylhexyl) phthalate, 6:2 chlorinated polyfluorinated ether sulfonate, and chlorpyrifos results in the downregulation of tetrapod Sox9 and/or zebrafish sox9b. Disruption of Sox9/sox9b function through environmental exposures or genetic mutations produce a wide range of phenotypes and adversely affect organ development and health. We generated a dominant-negative sox9b (dnsox9b) to inhibit sox9b target gene expression and used the Gal4/UAS system to drive dnsox9b specifically in cardiomyocytes. Cardiomyocyte-specific inhibition of sox9b function resulted in a decrease in ventricular cardiomyocytes, an increase in atrial cardiomyocytes, hypoplastic endothelial cushions, and impaired epicardial development, ultimately culminating in heart failure. Cardiomyocyte-specific dnsox9b expression significantly reduced end diastolic volume, which corresponded with a decrease in stroke volume, ejection fraction, and cardiac output. Further analysis of isolated cardiac tissue by RT-qPCR revealed cardiomyocyte-specific inhibition of sox9b function significantly decreased the expression of the critical cardiac development genes nkx2.5, nkx2.7, and myl7, as well as c-fos, an immediate early gene necessary for cardiomyocyte progenitor differentiation. Together our studies indicate sox9b transcriptional regulation is necessary for cardiomyocyte development and function.

Gja1 expression is regulated by cooperation between SOX8/SOX9 and cJUN transcription factors in TM4 and 15P-1 Sertoli cell lines

Within the seminiferous tubules of the testis, Gja1-encoded connexin43 plays a critical role in intercellular communication between Sertoli cells. These cells nurture, protect and stimulate the developing germ cells and spermatids. SOX transcription factors are known to play an important role in male fertility and sex determination; however, their physiological function and the identity of their target genes in postnatal Sertoli cells remain to be defined. Members of the activating protein-1 (AP-1) family have been shown to regulate Gja1 expression in myometrial and testicular cells and to physically interact with SOX members, suggesting that these transcription factors may regulate its expression within the testis. Hence, we performed co-transfections of expression plasmids encoding SOX4, SOX8, SOX9 and cJUN with different mouse Gja1 promoter/luciferase reporter constructs within TM4 and 15P-1 Sertoli cells. We showed that a functional cooperation between cJUN and SOX8 or SOX9 regulates Gja1 expression and may involve DNA regulatory elements located between -132 and -26 bp. Such synergy relies on the recruitment of cJUN to the -47 base pair (bp) AP-1 DNA regulatory element of the mouse Gja1 promoter. Hence, SOX and AP-1 members cooperate to regulate Gja1 within testicular Sertoli cells.

A transition from SoxB1 to SoxE transcription factors is essential for progression from pluripotent blastula cells to neural crest cells

The neural crest is a stem cell population unique to vertebrate embryos that gives rise to derivatives from multiple embryonic germ layers. The molecular underpinnings of potency that govern neural crest potential are highly conserved with that of pluripotent blastula stem cells, suggesting that neural crest cells may have evolved through retention of aspects of the pluripotency gene regulatory network (GRN). A striking difference in the regulatory factors utilized in pluripotent blastula cells and neural crest cells is the deployment of different sub-families of Sox transcription factors; SoxB1 factors play central roles in the pluripotency of naïve blastula and ES cells, whereas neural crest cells require SoxE function. Here we explore the shared and distinct activities of these factors to shed light on the role that this molecular hand-off of Sox factor activity plays in the genesis of neural crest and the lineages derived from it. Our findings provide evidence that SoxB1 and SoxE factors have both overlapping and distinct activities in regulating pluripotency and lineage restriction in the embryo. We hypothesize that SoxE factors may transiently replace SoxB1 factors to control pluripotency in neural crest cells, and then poise these cells to contribute to glial, chondrogenic and melanocyte lineages at stages when SoxB1 factors promote neuronal progenitor formation.

A Modular Platform for Differentiation of Human PSCs into All Major Ectodermal Lineages

Directing the fate of human pluripotent stem cells (hPSCs) into different lineages requires variable starting conditions and components with undefined activities, introducing inconsistencies that confound reproducibility and assessment of specific perturbations. Here we introduce a simple, modular protocol for deriving the four main ectodermal lineages from hPSCs. By precisely varying FGF, BMP, WNT, and TGFβ pathway activity in a minimal, chemically defined medium, we show parallel, robust, and reproducible derivation of neuroectoderm, neural crest (NC), cranial placode (CP), and non-neural ectoderm in multiple hPSC lines, on different substrates independently of cell density. We highlight the utility of this system by interrogating the role of TFAP2 transcription factors in ectodermal differentiation, revealing the importance of TFAP2A in NC and CP specification, and performing a small-molecule screen that identified compounds that further enhance CP differentiation. This platform provides a simple stage for systematic derivation of the entire range of ectodermal cell types.

Specifying neural crest cells: From chromatin to morphogens and factors in between

Neural crest (NC) cells are a stem-like multipotent population of progenitor cells that are present in vertebrate embryos, traveling to various regions in the developing organism. Known as the "fourth germ layer," these cells originate in the ectoderm between the neural plate (NP), which will become the brain and spinal cord, and nonneural tissues that will become the skin and the sensory organs. NC cells can differentiate into more than 30 different derivatives in response to the appropriate signals including, but not limited to, craniofacial bone and cartilage, sensory nerves and ganglia, pigment cells, and connective tissue. The molecular and cellular mechanisms that control the induction and specification of NC cells include epigenetic control, multiple interactive and redundant transcriptional pathways, secreted signaling molecules, and adhesion molecules. NC cells are important not only because they transform into a wide variety of tissue types, but also because their ability to detach from their epithelial neighbors and migrate throughout developing embryos utilizes mechanisms similar to those used by metastatic cancer cells. In this review, we discuss the mechanisms required for the induction and specification of NC cells in various vertebrate species, focusing on the roles of early morphogenesis, cell adhesion, signaling from adjacent tissues, and the massive transcriptional network that controls the formation of these amazing cells. This article is categorized under: Nervous System Development > Vertebrates: General Principles Gene Expression and Transcriptional Hierarchies > Regulatory Mechanisms Gene Expression and Transcriptional Hierarchies > Gene Networks and Genomics Signaling Pathways > Cell Fate Signaling.

SHP2 regulates skeletal cell fate by modifying SOX9 expression and transcriptional activity

Chondrocytes and osteoblasts differentiate from a common mesenchymal precursor, the osteochondroprogenitor (OCP), and help build the vertebrate skeleton. The signaling pathways that control lineage commitment for OCPs are incompletely understood. We asked whether the ubiquitously expressed protein-tyrosine phosphatase SHP2 (encoded by Ptpn11) affects skeletal lineage commitment by conditionally deleting Ptpn11 in mouse limb and head mesenchyme using "Cre-loxP"-mediated gene excision. SHP2-deficient mice have increased cartilage mass and deficient ossification, suggesting that SHP2-deficient OCPs become chondrocytes and not osteoblasts. Consistent with these observations, the expression of the master chondrogenic transcription factor SOX9 and its target genes Acan, Col2a1, and Col10a1 were increased in SHP2-deficient chondrocytes, as revealed by gene expression arrays, qRT-PCR, in situ hybridization, and immunostaining. Mechanistic studies demonstrate that SHP2 regulates OCP fate determination via the phosphorylation and SUMOylation of SOX9, mediated at least in part via the PKA signaling pathway. Our data indicate that SHP2 is critical for skeletal cell lineage differentiation and could thus be a pharmacologic target for bone and cartilage regeneration.

ERK-mediated phosphorylation regulates SOX10 sumoylation and targets expression in mutant BRAF melanoma

In human mutant BRAF melanoma cells, the stemness transcription factor FOXD3 is rapidly induced by inhibition of ERK1/2 signaling and mediates adaptive resistance to RAF inhibitors. However, the mechanism underlying ERK signaling control of FOXD3 expression remains unknown. Here we show that SOX10 is both necessary and sufficient for RAF inhibitor-induced expression of FOXD3 in mutant BRAF melanoma cells. SOX10 activates the transcription of FOXD3 by binding to a regulatory element in FOXD3 promoter. Phosphorylation of SOX10 by ERK inhibits its transcription activity toward multiple target genes by interfering with the sumoylation of SOX10 at K55, which is essential for its transcription activity. Finally, depletion of SOX10 sensitizes mutant BRAF melanoma cells to RAF inhibitors in vitro and in vivo. Thus, our work discovers a novel phosphorylation-dependent regulatory mechanism of SOX10 transcription activity and completes an ERK1/2/SOX10/FOXD3/ERBB3 axis that mediates adaptive resistance to RAF inhibitors in mutant BRAF melanoma cells.

Aberrant activation of the human sex-determining gene in early embryonic development results in postnatal growth retardation and lethality in mice

Sexual dimorphisms are prevalent in development, physiology and diseases in humans. Currently, the contributions of the genes on the male-specific region of the Y chromosome (MSY) in these processes are uncertain. Using a transgene activation system, the human sex-determining gene hSRY is activated in the single-cell embryos of the mouse. Pups with hSRY activated (hSRY^ON) are born of similar sizes as those of non-activated controls. However, they retard significantly in postnatal growth and development and all die of multi-organ failure before two weeks of age. Pathological and molecular analyses indicate that hSRY^ON pups lack innate suckling activities, and develop fatty liver disease, arrested alveologenesis in the lung, impaired neurogenesis in the brain and occasional myocardial fibrosis and minimized thymus development. Transcriptome analysis shows that, in addition to those unique to the respective organs, various cell growth and survival pathways and functions are differentially affected in the transgenic mice. These observations suggest that ectopic activation of a Y-located SRY gene could exert male-specific effects in development and physiology of multiple organs, thereby contributing to sexual dimorphisms in normal biological functions and disease processes in affected individuals.

SUMO and the robustness of cancer

Post-translational protein modification by small ubiquitin-like modifier (SUMO), termed sumoylation, is an important mechanism in cellular responses to stress and one that appears to be upregulated in many cancers. Here, we examine the role of sumoylation in tumorigenesis as a possibly necessary safeguard that protects the stability and functionality of otherwise easily misregulated gene expression programmes and signalling pathways of cancer cells.

Sumoylation in Craniofacial Disorders

Craniofacial development requires a complex series of coordinated and finely tuned events to take place, during a relatively short time frame. These events are set in motion by switching on and off transcriptional cascades that involve the use of numerous signalling pathways and a multitude of factors that act at the site of gene transcription. It is now well known that amidst the subtlety of this process lies the intricate world of protein modification, and the posttranslational addition of the small ubiquitin -like modifier, SUMO, is an example that has been implicated in this process. Many proteins that are required for formation of various structures in the embryonic head and face adapt specific functions with SUMO modification. Interestingly, the main clinical phenotype reported for a disruption of the SUMO1 locus is the common birth defect cleft lip and palate. In this chapter therefore, we discuss the role of SUMO1 in craniofacial development, with emphasis on orofacial clefts. We suggest that these defects can be a sensitive indication of down regulated SUMO modification at a critical stage during embryogenesis. As well as specific mutations affecting the ability of particular proteins to be sumoylated, non-genetic events may have the effect of down-regulating the SUMO pathway to give the same result. Enzymes regulating the SUMO pathway may become important therapeutic targets in the preventative and treatment therapies for craniofacial defects in the future.

SOX9 and the many facets of its regulation in the chondrocyte lineage

SOX9 is a pivotal transcription factor in developing and adult cartilage. Its gene is expressed from the multipotent skeletal progenitor stage and is active throughout chondrocyte differentiation. While it is repressed in hypertrophic chondrocytes in cartilage growth plates, it remains expressed throughout life in permanent chondrocytes of healthy articular cartilage. SOX9 is required for chondrogenesis: it secures chondrocyte lineage commitment, promotes cell survival, and transcriptionally activates the genes for many cartilage-specific structural components and regulatory factors. Since heterozygous mutations within and around SOX9 were shown to cause the severe skeletal malformation syndrome called campomelic dysplasia, researchers around the world have worked assiduously to decipher the many facets of SOX9 actions and regulation in chondrogenesis. The more we learn, the more we realize the complexity of the molecular networks in which SOX9 fulfills its functions and is regulated at the levels of its gene, RNA, and protein, and the more we measure the many gaps remaining in knowledge. At the same time, new technologies keep giving us more means to push further the frontiers of knowledge. Research efforts must be pursued to fill these gaps and to better understand and treat many types of cartilage diseases in which SOX9 has or could have a critical role. These diseases include chondrodysplasias and cartilage degeneration diseases, namely osteoarthritis, a prevalent and still incurable joint disease. We here review the current state of knowledge of SOX9 actions and regulation in the chondrocyte lineage, and propose new directions for future fundamental and translational research projects.

FBW7 suppression leads to SOX9 stabilization and increased malignancy in medulloblastoma

SOX9 is a master transcription factor that regulates development and stem cell programs. However, its potential oncogenic activity and regulatory mechanisms that control SOX9 protein stability are poorly understood. Here, we show that SOX9 is a substrate of FBW7, a tumor suppressor, and a SCF (SKP1/CUL1/F‐box)‐type ubiquitin ligase. FBW7 recognizes a conserved degron surrounding threonine 236 (T236) in SOX9 that is phosphorylated by GSK3 kinase and consequently degraded by SCF^FBW7α. Failure to degrade SOX9 promotes migration, metastasis, and treatment resistance in medulloblastoma, one of the most common childhood brain tumors. FBW7 is either mutated or downregulated in medulloblastoma, and in cases where FBW7 mRNA levels are low, SOX9 protein is significantly elevated and this phenotype is associated with metastasis at diagnosis and poor patient outcome. Transcriptional profiling of medulloblastoma cells expressing a degradation‐resistant SOX9 mutant reveals activation of pro‐metastatic genes and genes linked to cisplatin resistance. Finally, we show that pharmacological inhibition of PI3K/AKT/mTOR pathway activity destabilizes SOX9 in a GSK3/FBW7‐dependent manner, rendering medulloblastoma cells sensitive to cytostatic treatment.

The role of post-translational modifications in hearing and deafness

Post-translational modifications (PTMs) are key molecular events that modify proteins after their synthesis and modulate their ultimate functional properties by affecting their stability, localisation, interaction potential or activity. These chemical changes expand the size of the proteome adding diversity to the molecular pathways governing the biological outcome of cells. PTMs are, thus, crucial in regulating a variety of cellular processes such as apoptosis, proliferation and differentiation and have been shown to be instrumental during embryonic development. In addition, alterations in protein PTMs have been implicated in the pathogenesis of many human diseases, including deafness. In this review, we summarize the recent progress made in understanding the roles of PTMs during cochlear development, with particular emphasis on the enzymes driving protein phosphorylation, acetylation, methylation, glycosylation, ubiquitination and SUMOylation. We also discuss how these enzymes may contribute to hearing impairment and deafness.

Sox2: To crest or not to crest?

Precise control of neural progenitor transformation into neural crest stem cells ensures proper craniofacial and head development. In the neural progenitor pool, SoxB factors play an essential role as cell fate determinants of neural development, whereas during neural crest stem cell formation, Sox2 plays a predominant role as a guardian of the developmental clock that ensures precision of cell flow in the developing head.

SoxE factors: Transcriptional regulators of neural differentiation and nervous system development

Sox8, Sox9 and Sox10 represent the three vertebrate members of the SoxE subclass of high-mobility-group domain containing Sox transcription factors. They play important roles in the peripheral and central nervous systems as regulators of stemness, specification, survival, lineage progression, glial differentiation and homeostasis. Functions are frequently overlapping, but sometimes antagonistic. SoxE proteins dynamically interact with transcriptional regulators, chromatin changing complexes and components of the transcriptional machinery. By establishing regulatory circuits with other transcription factors and microRNAs, SoxE proteins perform divergent functions in several cell lineages of the vertebrate nervous system, and at different developmental stages in the same cell lineage. The underlying molecular mechanisms are the topic of this review.

Dimerization and Transactivation Domains as Candidates for Functional Modulation and Diversity of Sox9

Sox9 plays an important role in a large variety of developmental pathways in vertebrates. It is composed of three domains: high-mobility group box (HMG box), dimerization (DIM) and transactivation (TAD). One of the main processes for regulation and variability of the pathways involving Sox9 is the self-gene expression regulation of Sox9. However, the subsequent roles of the Sox9 domains can also generate regulatory modulations. Studies have shown that TADs can bind to different types of proteins and its function seems to be influenced by DIM. Therefore, we hypothesized that both domains are directly associated and can be responsible for the functional variability of Sox9. We applied a method based on a broad phylogenetic context, using sequences of the HMG box domain, to ensure the homology of all the Sox9 copies used herein. The data obtained included 4,921 sequences relative to 657 metazoan species. Based on coevolutionary and selective pressure analyses of the Sox9 sequences, we observed coevolutions involving DIM and TADs. These data, along with the experimental data from literature, indicate a functional relationship between these domains. Moreover, DIM and TADs may be responsible for the functional plasticity of Sox9 because they are more tolerant for molecular changes (higher Ka/Ks ratio than the HMG box domain). This tolerance could allow a differential regulation of target genes or promote novel targets during transcriptional activation. In conclusion, we suggest that DIM and TADs functional association may regulate differentially the target genes or even promote novel targets during transcription activation mediated by Sox9 paralogs, contributing to the subfunctionalization of Sox9a and Sox9b in teleosts.

Efficient Generation of Gene-Modified Pigs Harboring Precise Orthologous Human Mutation via CRISPR/Cas9-Induced Homology-Directed Repair in Zygotes

Precise genetic mutation of model animals is highly valuable for functional investigation of human mutations. Clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated 9 (Cas9)-induced homology-directed repair (HDR) is usually used for precise genetic mutation, being limited by the relatively low efficiency compared with that of non-homologous end joining (NHEJ). Although inhibition of NHEJ was shown to enhance HDR-derived mutation, in this work, without inhibition of NHEJ, we first generated gene-modified pigs harboring precise orthologous human mutation (Sox10 c.A325>T) via CRISPR/Cas9-induced HDR in zygotes using single-strand oligo DNA (ssODN) as template with an efficiency as high as 80%, indicating that pig zygotes exhibited high activities of HDR relative to NHEJ and were highly amendable to genetic mutation via CIRSPR/Cas9-induced HDR. Besides, we found a higher concentration of ssODN remarkably reduced HDR-derived mutation in pig zygotes, suggesting a possible balance for optimal HDR-derived mutation in zygotes between the excessive accessibility to HDR templates and the activities of HDR relative to NHEJ which appeared to be negatively correlated to ssODN concentration. In addition, the HDR-derived mutation, as well as those from NHEJ, extensively integrated into various tissues including gonad of founder pig without detected off-targeting, suggesting CRISPR/Cas9-induced HDR in zygotes is a reliable approach for precise genetic mutation in pigs.

Neural crest specification by Prohibitin1 depends on transcriptional regulation of prl3 and vangl1

A complex network of transcription factors regulates specification of neural crest cells at early neurula stage by stabilizing neural crest identity and activating neural crest effector genes so that distinct subpopulations evolve. In this network, c-myc acts on top of the gene hierarchy controlling snail2, AP2 and prohibitin1 (phb1) expression. While snail2 and AP2 are well studied neural crest specifier genes little is known about the role of phb1 in this process. To identify phb1 regulated genes we analyzed the transcriptome of neural crest explants of phb1 morphant Xenopus embryos. Among 147 phb1 regulated genes we identified the membrane-associated protein-tyrosine phosphatase PRP4A3 (prl3) and the atypical cadherin and Wnt-PCP component van gogh like1 (vangl1). Gain of function, loss of function and epistasis experiments allowed us to allocate both genes in the neural crest specification network between phb1 and twist. Interestingly, both, vangl1 and prl3 regulate only a small subset of neural crest marker genes. The identification of two membrane-associated proteins as novel neural crest specifiers indicates that in addition to gene regulation by combinatory effects of transcription factors also post-translational modifications (prl3) and cell-cell adhesion and/or regulation of cell-polarity (vangl1) specify the identity of neural crest cell populations. genesis 53:627-639, 2015. © 2015 Wiley Periodicals, Inc.

SOX family transcription factors involved in diverse cellular events during development

In metazoa, SOX family transcription factors play many diverse roles. In vertebrate, they are well-known regulators of numerous developmental processes. Wide-ranging studies have demonstrated the co-expression of SOX proteins in various developing tissues and that they occur in an overlapping manner and show functional redundancy. In particular, studies focusing on the HMG box of SOX proteins have revealed that the HMG box regulates DNA-binding properties, and mediates both the nucleocytoplasmic shuttling of SOX proteins and their physical interactions with partner proteins. Posttranslational modifications are further implicated in the regulation of the transcriptional activities of SOX proteins. In this review, we discuss the underlying molecular mechanisms involved in the SOX-partner factor interactions and the functional modes of SOX-partner complexes during development. We particularly emphasize the representative roles of the SOX group proteins in major tissues during developmental and physiological processes.

Loss of SOX9 Expression Is Associated with PSA Recurrence in ERG-Positive and PTEN Deleted Prostate Cancers

The transcription factor SOX9 plays a crucial role in normal prostate development and has been suggested to drive prostate carcinogenesis in concert with PTEN inactivation. To evaluate the clinical impact of SOX9 and its relationship with key genomic alterations in prostate cancer, SOX9 expression was analyzed by immunohistochemistry on a tissue microarray containing 11,152 prostate cancers. Data on ERG status and deletions of PTEN, 3p13, 5q21 and 6q15 were available from earlier studies. SOX9 expression levels were comparable in luminal cells of normal prostate glands (50% SOX9 positive) and 3,671 cancers lacking TMPRSS2:ERG fusion (55% SOX9 positive), but was markedly increased in 3,116 ERG-fusion positive cancers (81% SOX9 positive, p<0.0001). While no unequivocal changes in the SOX9 expression levels were found in different stages of ERG-negative cancers, a gradual decrease of SOX9 paralleled progression to advanced stage, high Gleason grade, metastatic growth, and presence of PTEN deletions in ERG-positive cancers (p<0.0001 each). SOX9 levels were unrelated to deletions of 3p, 5q, and 6q. Down-regulation of SOX9 expression was particularly strongly associated with PSA recurrence in ERG-positive tumors harboring PTEN deletions (p=0.001), but had no significant effect in ERG-negative cancers or in tumors with normal PTEN copy numbers. In summary, the results of our study argue against a tumor-promoting role of SOX9 in prostate cancer, but demonstrate that loss of SOX9 expression characterizes a particularly aggressive subset of ERG positive cancers harboring PTEN deletions.

SOX9 accelerates ESC differentiation to three germ layer lineages by repressing SOX2 expression through P21 (WAF1/CIP1)

Upon removal of culture conditions that maintain an undifferentiated state, mouse embryonic stem cells (ESCs) differentiate into various cell types. Differentiation can be facilitated by forced expression of certain transcription factors (TFs), each of which can generally specify a particular developmental lineage. We previously established 137 mouse ESC lines, each of which carried a doxycycline-controllable TF. Among them, Sox9 has unique capacity: its forced expression accelerates differentiation of mouse ESCs into cells of all three germ layers. With the additional use of specific culture conditions, overexpression of Sox9 facilitated the generation of endothelial cells, hepatocytes and neurons from ESCs. Furthermore, Sox9 action increases formation of p21 (WAF1/CIP1), which then binds to the SRR2 enhancer of pluripotency marker Sox2 and inhibits its expression. Knockdown of p21 abolishes inhibition of Sox2 and Sox9-accelerated differentiation, and reduction of Sox2 2 days after the beginning of ESC differentiation can comparably accelerate mouse ESC formation of cells of three germ layers. These data implicate the involvement of the p21-Sox2 pathway in the mechanism of accelerated ESC differentiation by Sox9 overexpression. The molecular cascade could be among the first steps to program ESC differentiation.

Regulation of epithelial-mesenchymal transition through SUMOylation of transcription factors

Carcinoma cells can transition from an epithelial-to-mesenchymal differentiation state through a process known as epithelial-mesenchymal transition (EMT). The process of EMT is characterized by alterations in the pattern of gene expression and is associated with a loss of cell polarity, an increase in invasiveness, and an increase in cells expressing cancer stem cell (CSC) markers. The reverse process of mesenchymal-to-epithelial transition (MET) can also occur, though the transitions characterizing EMT and MET can be incomplete. A growing number of transcription factors have been identified that influence the EMT/MET processes. Interestingly, SUMOylation regulates the functional activity of many of the transcription factors governing transitions between epithelial and mesenchymal states. In some cases, the transcription factor is a small ubiquitin-like modifier conjugated directly, thus altering its transcriptional activity or cell trafficking. In other cases, SUMOylation alters transcriptional mechanisms through secondary effects. This review explores the role of SUMOylation in controlling transcriptional mechanisms that regulate EMT/MET in cancer. Developing new drugs that specifically target SUMOylation offers a novel therapeutic approach to block tumor growth and metastasis.

The versatile functions of Sox9 in development, stem cells, and human diseases

The transcription factor Sox9 was first discovered in patients with campomelic dysplasia, a haploinsufficiency disorder with skeletal deformities caused by dysregulation of Sox9 expression during chondrogenesis. Since then, its role as a cell fate determiner during embryonic development has been well characterized; Sox9 expression differentiates cells derived from all three germ layers into a large variety of specialized tissues and organs. However, recent data has shown that ectoderm- and endoderm-derived tissues continue to express Sox9 in mature organs and stem cell pools, suggesting its role in cell maintenance and specification during adult life. The versatility of Sox9 may be explained by a combination of post-transcriptional modifications, binding partners, and the tissue type in which it is expressed. Considering its importance during both development and adult life, it follows that dysregulation of Sox9 has been implicated in various congenital and acquired diseases, including fibrosis and cancer. This review provides a summary of the various roles of Sox9 in cell fate specification, stem cell biology, and related human diseases. Ultimately, understanding the mechanisms that regulate Sox9 will be crucial for developing effective therapies to treat disease caused by stem cell dysregulation or even reverse organ damage.