Defective importin beta recognition and nuclear import of the sex-determining factor SRY are associated with XY sex-reversing mutations

Role of nucleobase-specific interactions in binding and bending of DNA by human male sex-determination factor SRY

Y-chromosome-encoded master transcription factor SRY functions in the embryogenesis of therian mammals to initiate male development. Through interactions of its conserved high mobility-group (HMG) box within a widened DNA minor groove, SRY and related Sox factors induce sharp bends at specific DNA target sites. Here, we present the crystal structure of the SRY HMG domain bound to a DNA site containing consensus element 5'-ATTGTT. The structure contains three complexes in the asymmetric unit; in each complex, SRY forms 10 hydrogen bonds with minor-groove base atoms in 5'-CATTGT/ACAATG-3', shifting the recognition sequence by one base pair (italics). These nucleobase interactions involve conserved residues Arg7, Asn10, and Tyr74 on one side of intercalated Ile13 (the cantilever side chain), and Arg20, Asn32 and Ser36 on the other. Unlike the less-bent NMR structure, DNA bend angles of the distinct box-DNA complexes range from 69-84°, similar to those observed in homologous Sox domain-DNA structures. Electrophoretic studies indicate that respective substitutions of Asn32, Ser36 or Tyr74 by Ala exhibit slightly attenuated specific DNA-binding affinity and bend angles (70-73°) relative to WT (79°). By contrast, respective substitutions of Arg7, Asn10 or Arg20 by Ala markedly impaired DNA-binding affinity in association with much smaller DNA bend angles (53-65°). In a rodent cell-based model of the embryonic gonadal ridge, full-length SRY variants bearing these respective, Ala substitutions exhibited significantly decreased transcriptional activation of SRY's principal target gene (Sox9). Together, our findings suggest that nucleobase-specific hydrogen bonds by SRY are critical for specific DNA binding, bending, and transcriptional activation.

Disruption of the foxe1 gene in zebrafish reveals conserved functions in development of the craniofacial skeleton and the thyroid

Introduction: Mutations in the FOXE1 gene are implicated in cleft palate and thyroid dysgenesis in humans.

Methods: To investigate whether zebrafish could provide meaningful insights into the etiology of developmental defects in humans related to FOXE1, we generated a zebrafish mutant that has a disruption in the nuclear localization signal in the foxe1 gene, thereby restraining nuclear access of the transcription factor. We characterized skeletal development and thyroidogenesis in these mutants, focusing on embryonic and larval stages.

Results: Mutant larvae showed aberrant skeletal phenotypes in the ceratohyal cartilage and had reduced whole body levels of Ca, Mg and P, indicating a critical role for foxe1 in early skeletal development. Markers of bone and cartilage (precursor) cells were differentially expressed in mutants in post-migratory cranial neural crest cells in the pharyngeal arch at 1 dpf, at induction of chondrogenesis at 3 dpf and at the start of endochondral bone formation at 6 dpf. Foxe1 protein was detected in differentiated thyroid follicles, suggesting a role for the transcription factor in thyroidogenesis, but thyroid follicle morphology or differentiation were unaffected in mutants.

Discussion: Taken together, our findings highlight the conserved role of Foxe1 in skeletal development and thyroidogenesis, and show differential signaling of osteogenic and chondrogenic genes related to foxe1 mutation.

Tenuous Transcriptional Threshold of Human Sex Determination. I. SRY and Swyer Syndrome at the Edge of Ambiguity

Male sex determination in mammals is initiated by SRY, a Y-encoded transcription factor. The protein contains a high-mobility-group (HMG) box mediating sequence-specific DNA bending. Mutations causing XY gonadal dysgenesis (Swyer syndrome) cluster in the box and ordinarily arise de novo. Rare inherited variants lead to male development in one genetic background (the father) but not another (his sterile XY daughter). De novo and inherited mutations occur at an invariant Tyr adjoining the motif's basic tail (box position 72; Y127 in SRY). In SRY-responsive cell lines CH34 and LNCaP, de novo mutations Y127H and Y127C reduced SRY activity (as assessed by transcriptional activation of principal target gene Sox9) by 5- and 8-fold, respectively. Whereas Y127H impaired testis-specific enhancer assembly, Y127C caused accelerated proteasomal proteolysis; activity was in part rescued by proteasome inhibition. Inherited variant Y127F was better tolerated: its expression was unperturbed, and activity was reduced by only twofold, a threshold similar to other inherited variants. Biochemical studies of wild-type (WT) and variant HMG boxes demonstrated similar specific DNA affinities (within a twofold range), with only subtle differences in sharp DNA bending as probed by permutation gel electrophoresis and fluorescence resonance-energy transfer (FRET); thermodynamic stabilities of the free boxes were essentially identical. Such modest perturbations are within the range of species variation. Whereas our cell-based findings rationalize the de novo genotype-phenotype relationships, a molecular understanding of inherited mutation Y127F remains elusive. Our companion study uncovers cryptic biophysical perturbations suggesting that the para-OH group of Y127 anchors a novel water-mediated DNA clamp.

Early Gonadal Development and Sex Determination in Mammal

Sex determination is crucial for the transmission of genetic information through generations. In mammal, this process is primarily regulated by an antagonistic network of sex-related genes beginning in embryonic development and continuing throughout life. Nonetheless, abnormal expression of these sex-related genes will lead to reproductive organ and germline abnormalities, resulting in disorders of sex development (DSD) and infertility. On the other hand, it is possible to predetermine the sex of animal offspring by artificially regulating sex-related gene expression, a recent research hotspot. In this paper, we reviewed recent research that has improved our understanding of the mechanisms underlying the development of the gonad and primordial germ cells (PGCs), progenitors of the germline, to provide new directions for the treatment of DSD and infertility, both of which involve manipulating the sex ratio of livestock offspring.

Tenuous transcriptional threshold of human sex determination. II. SRY exploits water-mediated clamp at the edge of ambiguity

Y-encoded transcription factor SRY initiates male differentiation in therian mammals. This factor contains a high-mobility-group (HMG) box, which mediates sequence-specific DNA binding with sharp DNA bending. A companion article in this issue described sex-reversal mutations at box position 72 (residue 127 in human SRY), invariant as Tyr among mammalian orthologs. Although not contacting DNA, the aromatic ring seals the domain's minor wing at a solvent-exposed junction with a basic tail. A seeming paradox was posed by the native-like biochemical properties of inherited Swyer variant Y72F: its near-native gene-regulatory activity is consistent with the father's male development, but at odds with the daughter's XY female somatic phenotype. Surprisingly, aromatic rings (Y72, F72 or W72) confer higher transcriptional activity than do basic or polar side chains generally observed at solvated DNA interfaces (Arg, Lys, His or Gln). Whereas biophysical studies (time-resolved fluorescence resonance energy transfer and heteronuclear NMR spectroscopy) uncovered only subtle perturbations, dissociation of the Y72F complex was markedly accelerated relative to wild-type. Studies of protein-DNA solvation by molecular-dynamics (MD) simulations of an homologous high-resolution crystal structure (SOX18) suggest that Y72 para-OH anchors a network of water molecules at the tail-DNA interface, perturbed in the variant in association with nonlocal conformational fluctuations. Loss of the Y72 anchor among SRY variants presumably "unclamps" its basic tail, leading to (a) rapid DNA dissociation despite native affinity and (b) attenuated transcriptional activity at the edge of sexual ambiguity. Conservation of Y72 suggests that this water-mediated clamp operates generally among SRY and metazoan SOX domains.

Generation and mutational analysis of a transgenic mouse model of human SRY

SRY is the Y-chromosomal gene that determines male sex development in humans and most other mammals. After three decades of study, we still lack a detailed understanding of which domains of the SRY protein are required to engage the pathway of gene activity leading to testis development. Some insight has been gained from the study of genetic variations underlying differences/disorders of sex determination (DSD), but the lack of a system of experimentally generating SRY mutations and studying their consequences in vivo has limited progress in the field. To address this issue, we generated a mouse model carrying a human SRY transgene able to drive testis determination in XX mice. Using CRISPR-Cas9 gene editing, we generated novel genetic modifications in each of SRY's three domains (N-terminal, HMG box, and C-terminal) and performed a detailed analysis of their molecular and cellular effects on embryonic testis development. Our results provide new functional insights unique to human SRY and present a versatile and powerful system in which to functionally analyze variations of SRY including known and novel pathogenic variants found in DSD.

Respiratory Syncytial Virus Matrix Protein-Chromatin Association Is Key to Transcriptional Inhibition in Infected Cells

The morbidity and mortality caused by the globally prevalent human respiratory pathogen respiratory syncytial virus (RSV) approaches that world-wide of influenza. We previously demonstrated that the RSV matrix (M) protein shuttles, in signal-dependent fashion, between host cell nucleus and cytoplasm, and that this trafficking is central to RSV replication and assembly. Here we analyze in detail the nuclear role of M for the first time using a range of novel approaches, including quantitative analysis of de novo cell transcription in situ in the presence or absence of RSV infection or M ectopic expression, as well as in situ DNA binding. We show that M, dependent on amino acids 110-183, inhibits host cell transcription in RSV-infected cells as well as cells transfected to express M, with a clear correlation between nuclear levels of M and the degree of transcriptional inhibition. Analysis of bacterially expressed M protein and derivatives thereof mutated in key residues within M's RNA binding domain indicates that M can bind to DNA as well as RNA in a cell-free system. Parallel results for point-mutated M derivatives implicate arginine 170 and lysine 172, in contrast to other basic residues such as lysine 121 and 130, as critically important residues for inhibition of transcription and DNA binding both in situ and in vitro. Importantly, recombinant RSV carrying arginine 170/lysine 172 mutations shows attenuated infectivity in cultured cells and in an animal model, concomitant with altered inflammatory responses. These findings define an RSV M-chromatin interface critical for host transcriptional inhibition in infection, with important implications for anti-RSV therapeutic development.

A novel SRY pathogenic variant from a 46,XY female harboring a nonsense point mutation (G to A) in position 293

46,XY female is a genetic disorder characterized by gonad gender not consistent with chromosomal sex. The SRY gene mutation is a common cause of 46,XY reversal type 1 (OMIM: 400044). Peripheral blood was collected from a 46,XY female patient and her father. Sex chromosomes were confirmed by karyotype analysis and fluorescence in situ hybridization (FISH) detection of the specific probe of sex chromosomes with cultured lymphocytes. After extracting blood genomic DNA, SRY characteristic fluorescence peak was detected by quantitative fluorescence PCR (QF-PCR) method. Whole exome was sequenced with NGS, and SRY gene was sequenced by Sanger sequencing, respectively. The chromosomes X and Y of the patient were confirmed by karyotype of 46,XY, and FISH specific probe of chromosome X and Y. SRY specific fluorescence peak was observed by QF-PCR. The whole-exome sequencing results showed chrY: 2655352(GRCh37): c.293G>A hemizygote mutation, confirmed by Sanger sequencing. The de novo mutation resulted in the mRNA encoding the tryptophan codon of 98 (UGG) change into a termination codon (UAG) (P.Trp98ter), and the translation process was terminated prematurely. The discovery of this novel mutation in the SRY gene helps elucidate the molecular mechanism of 46,XY female sex reversal and enriches such patients' genetic mutation spectrum.

Diverse Regulation but Conserved Function: SOX9 in Vertebrate Sex Determination

Sex determination occurs early during embryogenesis among vertebrates. It involves the differentiation of the bipotential gonad to ovaries or testes by a fascinating diversity of molecular switches. In most mammals, the switch is SRY (sex determining region Y); in other vertebrates it could be one of a variety of genes including Dmrt1 or dmy. Downstream of the switch gene, SOX9 upregulation is a central event in testes development, controlled by gonad-specific enhancers across the 2 Mb SOX9 locus. SOX9 is a ‘hub’ gene of gonadal development, regulated positively in males and negatively in females. Despite this diversity, SOX9 protein sequence and function among vertebrates remains highly conserved. This article explores the cellular, morphological, and genetic mechanisms initiated by SOX9 for male gonad differentiation.

A missense mutation (c.226C>A) in HMG box SRY gene affects nNLS function in 46,XY sex reversal female

The SRY initiates cascade of gene expression that transforms the undifferentiated gonad, genital ridge into testis. Mutations of the SRY gene is associated with complete gonadal dysgenesis in females with 46,XY karyotype. Primary amenorrhea is one of the clinical findings to express the genetic cause in 46,XY sex reversal. Here, we report a 26-year-old married woman presenting with primary amenorhea and complete gonadal dysgenesis. The clinical phenotypes were hypoplastic uterus with streak gonad and underdeveloped secondary sexual characters. The cytogenetic analysis confirmed 46,XY sex reversal karyotype of a female. Using molecular approach, we screened open reading frame of the SRY gene by PCR and targeted DNA Sanger sequencing. The patient was confirmed with nucleotide substitution (c.226C>A; p.Arg76Ser) at in HMG box domain of SRY gene that causes 46,XY sex reversal female. Mutation prediction algorithms suggest that alteration might be disease causing mutation and mutated (p.Arg76Ser) amino acid deleteriously affects HMG box nNLS region of SRY protein. Clinical phenotypes and in silico analysis confirmed that missense substitution (p.Arg76Ser) impaired nNLS binding Calmodulin-mediated nuclear transport of SRY from cytoplasm to nucleus. The mutation affects down regulation of male sex differentiation pathway and is responsible for 46,XY sex reversal female with gonadal dysgenesis.

Structural basis for nuclear import selectivity of pioneer transcription factor SOX2

SOX (SRY-related HMG-box) transcription factors perform critical functions in development and cell differentiation. These roles depend on precise nuclear trafficking, with mutations in the nuclear targeting regions causing developmental diseases and a range of cancers. SOX protein nuclear localization is proposed to be mediated by two nuclear localization signals (NLSs) positioned within the extremities of the DNA-binding HMG-box domain and, although mutations within either cause disease, the mechanistic basis has remained unclear. Unexpectedly, we find here that these two distantly positioned NLSs of SOX2 contribute to a contiguous interface spanning 9 of the 10 ARM domains on the nuclear import adapter IMPα3. We identify key binding determinants and show this interface is critical for neural stem cell maintenance and for Drosophila development. Moreover, we identify a structural basis for the preference of SOX2 binding to IMPα3. In addition to defining the structural basis for SOX protein localization, these results provide a platform for understanding how mutations and post-translational modifications within these regions may modulate nuclear localization and result in clinical disease, and also how other proteins containing multiple NLSs may bind IMPα through an extended recognition interface.

The SOX2 pioneer transcription factor performs critical roles in pluripotency and self-renewal of embryonic stem cells. Here the authors show that SOX2’s two nuclear localization signal sequences form a contiguous binding interface on the nuclear import receptor importin-α3, and provide a structural basis for the preference of SOX2 binding to IMPα3.

Inherited Missense Mutation Occurring in Arginine76 of the SRY Gene Does Not Account for Familial 46, XY Sex Reversal

BACKGROUND

SRY (sex determining region of Y) is one of the important genes involved in the process of human sex determination. The disturbed sex determination caused by an SRY mutation accounts for 10% to 15% of cases with 46, XY sex reversal. Recently, 3 distal enhancers were identified upstream of the SOX9 gene.

OBJECTIVES

The purpose of this study was to investigate the molecular etiology of 46, XY sex reversal in 3 familial patients and a sporadic patient.

DESIGN

Next-generation sequencing was used to reveal the genotype and inherited pattern. Copy number variations and single nucleotide polymorphism haplotyping were analyzed to observe the alteration of enhancers of SOX9. Transcriptional activity of SRY mutation were assessed by a dual luciferase reporting system, and nuclear translocation was observed by confocal microscopy.

RESULTS

Two novel SRY gene mutations, p.Arg76Leu and p.Glu89flx15, were identified. In the pedigree with multiple patients, p.Arg76Leu mutation in SRY and p.Gly212Ser mutation in NR5A1 were identified in the proband. The heterozygous deletion far upstream of the SOX9 gene in chromosome 17 was identified in the 3 patients in this family, containing the distal enhancer eSR-A of SOX9 but not eSR-B and eALDI. The frameshift mutation p.Glu89flx15 was revealed to inhibit the transcriptional activity of the target gene, whereas the missense mutation p.Arg76Leu barely showed an effect.

CONCLUSION

In contrast to sporadic cases, inherited single nucleotide variations of SRY are not the main cause of the severe phenotype of 46, XY sex reversal, and the enhancers of SOX9 should be investigated carefully in such patients.

A universal transportin protein drives stochastic choice of olfactory neurons via specific nuclear import of a sox-2-activating factor

Stochastic neuronal cell fate choice involving notch-independent mechanisms is a poorly understood biological process. The Caenorhabditis elegans AWC olfactory neuron pair asymmetrically differentiates into the default AWC^OFF and induced AWC^ON subtypes in a stochastic manner. Stochastic choice of the AWC^ON subtype is established using gap junctions and SLO BK potassium channels to repress a calcium-activated protein kinase pathway. However, it is unknown how the potassium channel-repressed calcium signaling is translated into the induction of the AWC^ON subtype. Here, we identify a detailed working mechanism of how the homeodomain-like transcription factor NSY-7, previously described as a repressor in the maintenance of AWC asymmetry, couples SLO BK potassium channels to transactivation of sox-2 expression for the induction of the AWC^ON subtype through the identification of a unique imb-2 (transportin 1) allele. imb-2 loss-of-function mutants are not viable; however, we identify a viable imb-2 allele from an unbiased forward genetic screen that reveals a specific role of imb-2 in AWC olfactory neuron asymmetry. IMB-2 specifically drives nuclear import of NSY-7 within AWC neurons to transactivate the expression of the high mobility group (HMG)-box transcription factor SOX-2 for the specification of the AWC^ON subtype. This study provides mechanistic insight into how NSY-7 couples SLO BK potassium channels to transactivation of sox-2 expression for the induction of the AWC^ON subtype. Our findings also provide structure-function insight into a conserved amino acid residue of transportins in brain development and suggest its dysfunction may lead to human neurological disorders.

New Therapeutic Approach for Targeting Hippo Signalling Pathway

Nuclear localization signals are short amino acid sequences that target proteins for nuclear import. In this manuscript, we have generated a chimeric tri-functional peptide composed of a cell penetrating peptide (CPP), a nuclear localization sequence and an interfering peptide blocking the interaction between TEAD and YAP, two transcription factors involved in the Hippo signalling pathway, whose deregulation is related to several types of cancer. We have validated the cell penetration and nuclear localization by flow cytometry and fluorescence microscopy and shown that the new generated peptide displays an apoptotic effect in tumor cell lines thanks to the specific nuclear delivery of the cargo, which targets a protein/protein interaction in the nucleus. In addition, the peptide has an anti-tumoral effect in vivo in xenograft models of breast cancer. The chimeric peptide designed in the current study shows encouraging prospects for developing nuclear anti- neoplastic drugs.

Late activation of the Raf/MEK/ERK pathway is required for translocation of the respiratory syncytial virus F protein to the plasma membrane and efficient viral replication

Activation of the Raf/MEK/ERK cascade is required for efficient propagation of several RNA and DNA viruses, including human respiratory syncytial virus (RSV). In RSV infection, activation of the Raf/MEK/ERK cascade is biphasic. An early induction within minutes after infection is associated with viral attachment. Subsequently, a second activation occurs with, so far, unknown function in the viral life cycle. In this study, we aimed to characterise the role of Raf/MEK/ERK-mediated signalling during ongoing RSV infection. Our data show that inhibition of the kinase MEK after the virus has been internalised results in a reduction of viral titers. Further functional investigations revealed that the late-stage activation of ERK is required for a specific step in RSV replication, namely, the secretory transport of the RSV fusion protein F. Thus, MEK inhibition resulted in impaired surface accumulation of the F protein. F protein surface expression is essential for efficient replication as it is involved in viral filament formation, cell fusion, and viral transmission. In summary, we provide detailed insights of how host cell signalling interferes with RSV replication and identified the Raf/MEK/ERK kinase cascade as potential target for novel anti-RSV strategies.

Nuclear localization signal targeting to macronucleus and micronucleus in binucleated ciliate Tetrahymena thermophila

Ciliated protozoa possess two morphologically and functionally distinct nuclei: a macronucleus (MAC) and a micronucleus (MIC). The MAC is transcriptionally active and functions in all cellular events. The MIC is transcriptionally inactive during cell growth, but functions in meiotic events to produce progeny nuclei. Thus, these two nuclei must be distinguished by the nuclear proteins required for their distinct functions during cellular events such as cell proliferation and meiosis. To understand the mechanism of the nuclear transport specific to either MAC or MIC, we identified specific nuclear localization signals (NLSs) in two MAC- and MIC-specific nuclear proteins, macronuclear histone H1 and micronuclear linker histone-like protein (Mlh1), respectively. By expressing GFP-fused fragments of these proteins in Tetrahymena thermophila cells, two distinct regions in macronuclear histone H1 protein were assigned as independent MAC-specific NLSs and two distinct regions in Mlh1 protein were assigned as independent MIC-specific NLSs. These NLSs contain several essential lysine residues responsible for the MAC- and MIC-specific nuclear transport, but neither contains any consensus sequence with known monopartite or bipartite NLSs in other model organisms. Our findings contribute to understanding how specific nuclear targeting is achieved to perform distinct nuclear functions in binucleated ciliates.

Identification of a novel mutation (Ala66Thr) of SRY gene causes XY pure gonadal dysgenesis by affecting DNA binding activity and nuclear import

Sex-determining region of the Y chromosome (SRY) gene plays a crucial role in male sexual differentiation and development. Several mutations in the SRY gene have been reported in the high mobility group (HMG) box domain and can cause gonadal dysgenesis symptoms. In this study, we report that a novel missense mutation in the SRY gene, a G to A transition within the HMG box, causes the Ala66Thr amino acid substitution in a female patient presenting 46,XY karyotype with pure gonadal dysgenesis. The G to A base transition was not found in the SRY sequence after the screening of 100 normal males. Furthermore, Ala66Thr mutation drastically reduced the binding capacity of SRY to DNA sequences, whereas wild-type SRY protein showed the normal binding capacity to DNA sequences in vitro. We also found that the mutant SRY protein was partly localized in cytoplasm, whereas wild-type SRY protein was strictly localized in cell nucleus. In addition, we analyzed the three-dimensional structure of SRY protein by homology modeling methods. In conclusion, we identified a novel SRY mutation in a 46,XY female patient with pure gonadal dysgenesis, demonstrating the importance of the Ala66Thr mutation in DNA binding activity and nuclear transport.

Nucleocytoplasmic shuttling of SOX14A and SOX14B transcription factors

The nucleocytoplasmic shuttling of SOX transcription factors play a crucial role in the regulation of SOX protein functions during development. In this study, we have demonstrated two nuclear localization signals in the HMG box of Eriocheir sinensis SOX14A and SOX14B. These two conserved nuclear localization signals mediate nuclear transport. The N-termini nuclear localization signal mediates the calmodulin-dependent pathway and the C-termini nuclear localization signal interacts with the importin-β pathway. The targeted deletion of nuclear localization signals of SOX14A/B dramatically inhibits the nuclear accumulation. We have first time revealed a non-classic nuclear export signal in the HMG box of E. sinensis SOX14A/B proteins is responds to leptomycin B. E. sinensis SOX14A/B is transported from the nucleus to the cytoplasm via a CRM1-dependent nuclear export pathway. And E. sinensis SOX14A/B are not belong to the subgroup E SOX proteins. Furthermore, these findings could shed a light on the mechanisms involved in the nuclear export of SOX proteins. The imperfect nuclear export signal on other SOX proteins, rather than just those of the SOXE group, may also be functional for nuclear export.

Reprint of: Importins in the maintenance and lineage commitment of ES cells

The nucleus of a eukaryotic cell is separated from the cytoplasm by a nuclear envelope, and nuclear pores within the envelope facilitate nucleocytoplasmic transport and the exchange of information. Gene regulation is a key component of biological activity regulation in the cell. Transcription factors control the expression levels of various genes that are necessary for the maintenance or conversion of cellular states during animal development. Because transcription factor activities determine the extent of transcription of target genes, the number of active transcription factors must be tightly regulated. In this regard, the nuclear translocation of a transcription factor is an important determinant of its activity. Therefore, it is becoming clear that the nucleocytoplasmic transport machinery is involved in cell differentiation and organism development. This review examines the regulation of transcription factors by the nucleocytoplasmic transport machinery in ES cells.

Importins in the maintenance and lineage commitment of ES cells

The nucleus of a eukaryotic cell is separated from the cytoplasm by a nuclear envelope, and nuclear pores within the envelope facilitate nucleocytoplasmic transport and the exchange of information. Gene regulation is a key component of biological activity regulation in the cell. Transcription factors control the expression levels of various genes that are necessary for the maintenance or conversion of cellular states during animal development. Because transcription factor activities determine the extent of transcription of target genes, the number of active transcription factors must be tightly regulated. In this regard, the nuclear translocation of a transcription factor is an important determinant of its activity. Therefore, it is becoming clear that the nucleocytoplasmic transport machinery is involved in cell differentiation and organism development. This review examines the regulation of transcription factors by the nucleocytoplasmic transport machinery in ES cells.

A Novel Missense Mutation 224G>T (R75M) in SRY Coding Region Interferes with Nuclear Import and Results in 46, XY Complete Gonadal Dysgenesis

SRY-mutation-caused sex reversal is a rare disease and mostly associated with a de novo mutation since the patients with defective SRY is infertile. There are many reports about SRY-mutation associated 46, XY ovarian disorder of sex development (DSD), but few described their molecular mechanism. Here we report a de novo mutation 224G>T (R75M) in SRY associated with a phenotypic female, 46, XY karyotype and dysgerminoma. The wild and mutated SRY were cloned into recombinant plasmid and expressed in cells in vitro, the result showed the mutated SRY is greatly accumulated in cytoplasm while the wild type SRY is mostly localized in nucleus. To make sure no other genes were involved, we performed the trio-based whole exome sequencing using the DNA samples from the proband and the parents, and no mutations were identified especially in DHH, NR0B1, NR5A1, SOX9 and MAP3K1, indicating the de novo mutation in SRY is the single defect responsible for the female sex reversal. We also used bioinformatics simulation analysis to predict impact of the mutation on SRY function, and find the R75 in wild type SRY can form a hydrogen bond with serine at 91 (S91) that make the SRY protein well fit into the minor groove of target DNA, while the M75 in the mutated SRY can't. Finally, we reviewed SRY mutations based on the available references and analyzed the mutation distribution patterns according to density and continuity, which may be useful for further study of the SRY structure, function, and its relatedness with DSD.

Human Sex Determination at the Edge of Ambiguity: INHERITED XY SEX REVERSAL DUE TO ENHANCED UBIQUITINATION AND PROTEASOMAL DEGRADATION OF A MASTER TRANSCRIPTION FACTOR

A general problem is posed by analysis of transcriptional thresholds governing cell fate decisions in metazoan development. A model is provided by testis determination in therian mammals. Its key step, Sertoli cell differentiation in the embryonic gonadal ridge, is initiated by SRY, a Y-encoded architectural transcription factor. Mutations in human SRY cause gonadal dysgenesis leading to XY female development (Swyer syndrome). Here, we have characterized an inherited mutation compatible with either male or female somatic phenotypes as observed in an XY father and XY daughter, respectively. The mutation (a crevice-forming substitution at a conserved back surface of the SRY high mobility group box) markedly destabilizes the domain but preserves specific DNA affinity and induced DNA bend angle. On transient transfection of diverse human and rodent cell lines, the variant SRY exhibited accelerated proteasomal degradation (relative to wild type) associated with increased ubiquitination; in vitro susceptibility to ubiquitin-independent ("default") cleavage by the 20S core proteasome was unchanged. The variant's gene regulatory activity (as assessed in a cellular model of the rat embryonic XY gonadal ridge) was reduced by 2-fold relative to wild-type SRY at similar levels of mRNA expression. Chemical proteasome inhibition restored native-like SRY expression and transcriptional activity in association with restored occupancy of a sex-specific enhancer element in principal downstream gene Sox9, demonstrating that the variant SRY exhibits essentially native activity on a per molecule basis. Our findings define a novel mechanism of impaired organogenesis, accelerated ubiquitin-directed proteasomal degradation of a master transcription factor leading to a developmental decision poised at the edge of ambiguity.

The proinflammatory role of HECTD2 in innate immunity and experimental lung injury

Invading pathogens may trigger overactivation of the innate immune system, which results in the release of large amounts of proinflammatory cytokines (cytokine storm) and leads to the development of pulmonary edema, multiorgan failure, and shock. PIAS1 is a multifunctional and potent anti-inflammatory protein that negatively regulates several key inflammatory pathways such as Janus kinase (JAK)-signal transducer and activator of transcription (STAT) and nuclear factor κB (NF-κB). We discovered a ubiquitin E3 ligase, HECTD2, which ubiquitinated and mediated the degradation of PIAS1, thus increasing inflammation in an experimental pneumonia model. We found that GSK3β phosphorylation of PIAS1 provided a phosphodegron for HECTD2 targeting. We also identified a mislocalized HECTD2 polymorphism, HECTD2(A19P), that was present in 8.5% of the population and functioned to reduce inflammation. This polymorphism prevented HECTD2/PIAS1 nuclear interaction, thus preventing PIAS1 degradation. The HECTD2(A19P) polymorphism was also protective toward acute respiratory distress syndrome (ARDS). We then developed a small-molecule inhibitor, BC-1382, that targeted HECTD2 and attenuated lipopolysaccharide (LPS)- and Pseudomonas aeruginosa-induced lung inflammation. These studies describe an unreported innate immune pathway and suggest that mutation or antagonism of the E3 ligase HECTD2 results in reduced severity of lung inflammation by selectively modulating the abundance of the anti-inflammatory protein PIAS1.

Nuclear Trafficking of the Rabies Virus Interferon Antagonist P-Protein Is Regulated by an Importin-Binding Nuclear Localization Sequence in the C-Terminal Domain

Rabies virus P-protein is expressed as five isoforms (P1-P5) which undergo nucleocytoplasmic trafficking important to roles in immune evasion. Although nuclear import of P3 is known to be mediated by an importin (IMP)-recognised nuclear localization sequence in the N-terminal region (N-NLS), the mechanisms underlying nuclear import of other P isoforms in which the N-NLS is inactive or has been deleted have remained unresolved. Based on the previous observation that mutation of basic residues K214/R260 of the P-protein C-terminal domain (P-CTD) can result in nuclear exclusion of P3, we used live cell imaging, protein interaction analysis and in vitro nuclear transport assays to examine in detail the nuclear trafficking properties of this domain. We find that the effect of mutation of K214/R260 on P3 is largely dependent on nuclear export, suggesting that nuclear exclusion of mutated P3 involves the P-CTD-localized nuclear export sequence (C-NES). However, assays using cells in which nuclear export is pharmacologically inhibited indicate that these mutations significantly inhibit P3 nuclear accumulation and, importantly, prevent nuclear accumulation of P1, suggestive of effects on NLS-mediated import activity in these isoforms. Consistent with this, molecular binding and transport assays indicate that the P-CTD mediates IMPα2/IMPβ1-dependent nuclear import by conferring direct binding to the IMPα2/IMPβ1 heterodimer, as well as to a truncated form of IMPα2 lacking the IMPβ-binding autoinhibitory domain (ΔIBB-IMPα2), and IMPβ1 alone. These properties are all dependent on K214 and R260. This provides the first evidence that P-CTD contains a genuine IMP-binding NLS, and establishes the mechanism by which P-protein isoforms other than P3 can be imported to the nucleus. These data underpin a refined model for P-protein trafficking that involves the concerted action of multiple NESs and IMP-binding NLSs, and highlight the intricate regulation of P-protein subcellular localization, consistent with important roles in infection.

A Novel SRY Gene Mutation p.F109L in a 46,XY Female with Complete Gonadal Dysgenesis

46,XY complete gonadal dysgenesis (CGD) is a disorder of sexual development that can result from different mutations in genes associated with sex determination. Patients are phenotypically females, and the disease is often diagnosed in late adolescence because of delayed puberty. Here, we present the clinical and molecular data of a 46,XY female CGD patient with gonadoblastoma with dysgerminoma and incidentally found inherited thrombophilia. The clinical significance of the described de novo SRY gene mutation c.325T>C (p.F109L) is discussed. This case report supports the critical role of the HGM domain in the SRY gene and the need of a multidisciplinary approach for CGD patients.

Fast track, dynein-dependent nuclear targeting of human immunodeficiency virus Vpr protein; impaired trafficking in a clinical isolate

Nuclear import of the accessory protein Vpr is central to infection by human immunodeficiency virus (HIV). We previously identified the Vpr F72L mutation in a HIV-infected, long-term non-progressor, showing that it resulted in reduced Vpr nuclear accumulation and altered cytoplasmic localisation. Here we demonstrate for the first time that the effects of nuclear accumulation of the F72L mutation are due to impairment of microtubule-dependent-enhancement of Vpr nuclear import. We use high resolution imaging approaches including fluorescence recovery after photobleaching and other approaches to document interaction between Vpr and the dynein light chain protein, DYNLT1, and impaired interaction of the F72L mutant with DYNLT1. The results implicate MTs/DYNLT1 as drivers of Vpr nuclear import and HIV infection, with important therapeutic implications.

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.

Subnuclear re-localization of SOX10 and p54NRB correlates with a unique neurological phenotype associated with SOX10 missense mutations

SOX10 is a transcription factor with well-known functions in neural crest and oligodendrocyte development. Mutations in SOX10 were first associated with Waardenburg-Hirschsprung disease (WS4; deafness, pigmentation defects and intestinal aganglionosis). However, variable phenotypes that extend beyond the WS4 definition are now reported. The neurological phenotypes associated with some truncating mutations are suggested to be the result of escape from the nonsense-mediated mRNA decay pathway; but, to date, no mechanism has been suggested for missense mutations, of which approximately 20 have now been reported, with about half of the latter shown to be redistributed to nuclear bodies of undetermined nature and function in vitro. Here, we report that p54NRB, which plays a crucial role in the regulation of gene expression during many cellular processes including differentiation, interacts synergistically with SOX10 to regulate several target genes. Interestingly, this paraspeckle protein, as well as two other members of the Drosophila behavior human splicing (DBHS) protein family, co-localize with SOX10 mutants in nuclear bodies, suggesting the possible paraspeckle nature of these foci or re-localization of the DBHS members to other subnuclear compartments. Remarkably, the co-transfection of wild-type and mutant SOX10 constructs led to the sequestration of wild-type protein in mutant-induced foci. In contrast to mutants presenting with additional cytoplasmic re-localization, those exclusively found in the nucleus alter synergistic activity between SOX10 and p54NRB. We propose that such a dominant negative effect may contribute to or be at the origin of the unique progressive and severe neurological phenotype observed in affected patients.

Hyper-dependence of breast cancer cell types on the nuclear transporter Importin β1

We previously reported that overexpression of members of the Importin (Imp) superfamily of nuclear transporters results in increased nuclear trafficking through conventional transport pathways in tumour cells. Here we show for the first time that the extent of overexpression of Impβ1 correlates with disease state in the MCF10 human breast tumour progression system. Excitingly, we find that targeting Impβ1 activity through siRNA is >30 times more efficient in decreasing the viability of malignant ductal carcinoma cells compared to isogenic non-transformed counterparts, and is highly potent and tumour selective at subnanomolar concentrations. Tumour cell selectivity of the siRNA effects was unique to Impβ1 and not other Imps, with flow cytometric analysis showing >60% increased cell death compared to controls concomitant with reduced nuclear import efficiency as indicated by confocal microscopic analysis. This hypersensitivity of malignant cell types to Impβ1 knockdown raises the exciting possibility of anti-cancer therapies targeted at Impβ1.

Enhanced tumour cell nuclear targeting in a tumour progression model

BACKGROUND

There is an urgent need for new approaches to deliver bioactive molecules to cancer cells efficiently and specifically.

METHODS

Here we fuse the cancer cell nuclear targeting module of the Chicken Anaemia Virus Apoptin protein to the core histones H2B and H3 and utilise them in transfection, protein transduction and DNA binding assays.

RESULTS

We found subsequent nuclear accumulation of these proteins to be 2-3 fold higher in tumour compared to normal cells in transfected isogenic human osteosarcoma and breast tumour progression models. This represents the first demonstration of enhanced nuclear targeting by Apoptin in a tumour progression model, and its functionality in a heterologous protein context. Excitingly, we found that the innate transduction ability of histones could be exploited in combination with the Apoptin nuclear targeting module to effect an overall 13-fold higher delivery of protein to osteosarcoma cancer cell nuclei compared to their isogenic normal counterparts.

CONCLUSIONS

This is the first report of cancer-cell specificity by a cell penetrating protein, with important implications for the use of protein transduction as a vehicle for gene/drug delivery in the future, and in particular in the development of highly specific and effective anti-cancer agents.

Structure-function relationships in human testis-determining factor SRY: an aromatic buttress underlies the specific DNA-bending surface of a high mobility group (HMG) box

Human testis determination is initiated by SRY, a Y-encoded architectural transcription factor. Mutations in SRY cause 46 XY gonadal dysgenesis with female somatic phenotype (Swyer syndrome) and confer a high risk of malignancy (gonadoblastoma). Such mutations cluster in the SRY high mobility group (HMG) box, a conserved motif of specific DNA binding and bending. To explore structure-function relationships, we constructed all possible substitutions at a site of clinical mutation (W70L). Our studies thus focused on a core aromatic residue (position 15 of the consensus HMG box) that is invariant among SRY-related HMG box transcription factors (the SOX family) and conserved as aromatic (Phe or Tyr) among other sequence-specific boxes. In a yeast one-hybrid system sensitive to specific SRY-DNA binding, the variant domains exhibited reduced (Phe and Tyr) or absent activity (the remaining 17 substitutions). Representative nonpolar variants with partial or absent activity (Tyr, Phe, Leu, and Ala in order of decreasing side-chain volume) were chosen for study in vitro and in mammalian cell culture. The clinical mutation (Leu) was found to markedly impair multiple biochemical and cellular activities as respectively probed through the following: (i) in vitro assays of specific DNA binding and protein stability, and (ii) cell culture-based assays of proteosomal degradation, nuclear import, enhancer DNA occupancy, and SRY-dependent transcriptional activation. Surprisingly, however, DNA bending is robust to this or the related Ala substitution that profoundly impairs box stability. Together, our findings demonstrate that the folding, trafficking, and gene-regulatory function of SRY requires an invariant aromatic "buttress" beneath its specific DNA-bending surface.

Regulation of male sex determination: genital ridge formation and Sry activation in mice

Sex determination is essential for the sexual reproduction to generate the next generation by the formation of functional male or female gametes. In mammals, primary sex determination is commenced by the presence or absence of the Y chromosome, which controls the fate of the gonadal primordium. The somatic precursor of gonads, the genital ridge is formed at the mid-gestation stage and gives rise to one of two organs, a testis or an ovary. The fate of the genital ridge, which is governed by the differentiation of somatic cells into Sertoli cells in the testes or granulosa cells in the ovaries, further determines the sex of an individual and their germ cells. Mutation studies in human patients with disorders of sex development and mouse models have revealed factors that are involved in mammalian sex determination. In most of mammals, a single genetic trigger, the Y-linked gene Sry (sex determination region on Y chromosome), regulates testicular differentiation. Despite identification of Sry in 1990, precise mechanisms underlying the sex determination of bipotential genital ridges are still largely unknown. Here, we review the recent progress that has provided new insights into the mechanisms underlying genital ridge formation as well as the regulation of Sry expression and its functions in male sex determination of mice.

Production of Sry knockout mouse using TALEN via oocyte injection

Recently developed transcription activator-like effector nuclease (TALEN) technology has enabled the creation of knockout mice, even for genes on the Y chromosome. In this study, we generated a knockout mouse for Sry, a sex-determining gene on the Y chromosome, using microinjection of TALEN RNA into pronuclear stage oocytes. As expected, the knockout mouse had female external and internal genitalia, a female level of blood testosterone and a female sexually dimorphic nucleus in the brain. The knockout mouse exhibited an estrous cycle and performed copulatory behavior as females, although it was infertile or had reduced fertility. A histological analysis showed that the ovary of the knockout mouse displayed a reduced number of oocytes and luteinized unruptured follicles, implying that a reduced number of ovulated oocytes is a possible reason for infertility and/or reduced fertility in the KO mouse.

A novel mutation (c. 341A>G) in the SRY gene in a 46,XY female patient with gonadal dysgenesis

SRY (sex-determining region Y) gene, MIM 480000, NM_005634) is crucial for sex differentiation which encodes the protein responsible for initiating testis differentiation. SRY mutations are associated with the presence of XY gonadal dysgenesis symptoms. We studied a 46,XY female patient with primary amenorrhoea and negative family history. The clinical, endocrine, histopathologic and cytogenetic data are consistent with gonadal dysgenesis. Using a molecular analysis, a novel (c.341A>G, p. N65D) missense mutation within the HMGbox of SRY gene was detected. Escherichia coli expression of SRY study showed reduced expression of the mutated protein and gel retardation assay method revealed lowered DNA-binding ability in N65D variant of SRY. The novel mutation detected in the SRY gene may be an aetiopathogenic factor in clinically defined 46,XY complete gonadal dysgenesis (CGD). Because of an increased risk of gonadoblastoma, proper early diagnosis and treatment prevent development of malignancies.

Disorders of sex development: new genes, new concepts

Formerly known as 'intersex' conditions, disorders of sex development (DSDs) are congenital conditions in which chromosomal, gonadal or anatomical sex is atypical. A complete revision of the nomenclature and classification of DSDs has been undertaken, which emphasizes the genetic aetiology of these disorders and discards pejorative terms. Uptake of the new terminology is widespread. DSDs affecting gonadal development are perhaps the least well understood. Unravelling the molecular mechanisms underlying gonadal development has revealed new causes of DSDs, although a specific molecular diagnosis is made in only ∼20% of patients. Conversely, identification of the molecular causes of DSDs has provided insight into the mechanisms of gonadal development. Studies of N-ethyl-N-nitrosourea mutagenesis in the mouse, and multigene diagnostic screening and genome-wide approaches, such as array-comparative genomic hybridization and next-generation sequencing, in patients with DSDs are accelerating the discovery of genes involved in gonadal development and DSDs. Furthermore, long-range gene regulatory mutations and multiple gene mutations are emerging as new causes of DSDs. Patients with DSDs, their parents and medical staff are confronted with challenging decisions regarding gender assignment, genital surgery and lifelong care. These advances are refining prognostic prediction and systematically improving the diagnosis and long-term management of children with DSDs.

A fresh look at the male-specific region of the human Y chromosome

The Chromosome-centric Human Proteome Project (C-HPP) aims to systematically map the entire human proteome with the intent to enhance our understanding of human biology at the cellular level. This project attempts simultaneously to establish a sound basis for the development of diagnostic, prognostic, therapeutic, and preventive medical applications. In Iran, current efforts focus on mapping the proteome of the human Y chromosome. The male-specific region of the Y chromosome (MSY) is unique in many aspects and comprises 95% of the chromosome's length. The MSY continually retains its haploid state and is full of repeated sequences. It is responsible for important biological roles such as sex determination and male fertility. Here, we present the most recent update of MSY protein-encoding genes and their association with various traits and diseases including sex determination and reversal, spermatogenesis and male infertility, cancers such as prostate cancers, sex-specific effects on the brain and behavior, and graft-versus-host disease. We also present information available from RNA sequencing, protein-protein interaction, post-translational modification of MSY protein-coding genes and their implications in biological systems. An overview of Human Y chromosome Proteome Project is presented and a systematic approach is suggested to ensure that at least one of each predicted protein-coding gene's major representative proteins will be characterized in the context of its major anatomical sites of expression, its abundance, and its functional relevance in a biological and/or medical context. There are many technical and biological issues that will need to be overcome in order to accomplish the full scale mapping.

70-kDa heat shock cognate protein hsc70 mediates calmodulin-dependent nuclear import of the sex-determining factor SRY

We recently showed that the developmentally important family of SOX (SRY (sex determining region on the Y chromosome)-related high mobility group (HMG) box) proteins require the calcium-binding protein calmodulin (CaM) for optimal nuclear accumulation, with clinical mutations in SRY that specifically impair nuclear accumulation via this pathway resulting in XY sex reversal. However, the mechanism by which CaM facilitates nuclear accumulation is unknown. Here, we show, for the first time, that the 70-kDa heat shock cognate protein hsc70 plays a key role in CaM-dependent nuclear import of SRY. Using a reconstituted nuclear import assay, we show that antibodies to hsc70 significantly reduce nuclear accumulation of wild type SRY and mutant derivatives thereof that retain CaM-dependent nuclear import, with an increased rate of nuclear accumulation upon addition of both CaM and hsc70, in contrast to an SRY mutant derivative with impaired CaM binding. siRNA knockdown of hsc70 in intact cells showed similar results, indicating clear dependence upon hsc70 for CaM-dependent nuclear import. Analysis using the technique of fluorescence recovery after photobleaching indicated that hsc70 is required for the maximal rate of SRY nuclear import in living cells but has no impact upon SRY nuclear retention/nuclear dynamics. Finally, we demonstrate direct binding of hsc70 to the SRY·CaM complex, with immunoprecipitation experiments from cell extracts showing association of hsc70 with wild type SRY, but not with a mutant derivative with impaired CaM binding, dependent on Ca(2+). Our novel findings strongly implicate hsc70 in CaM-dependent nuclear import of SRY.

Yeast importin-β is required for nuclear import of the Mig2 repressor

Background

Mig2 has been described as a transcriptional factor that in the absence of Mig1 protein is required for glucose repression of the SUC2 gene. Recently it has been reported that Mig2 has two different subcellular localizations. In high-glucose conditions it is a nuclear modulator of several Mig1-regulated genes, but in low-glucose most of the Mig2 protein accumulates in mitochondria. Thus, the Mig2 protein enters and leaves the nucleus in a glucose regulated manner. However, the mechanism by which Mig2 enters into the nucleus was unknown until now.

Results

Here, we report that the Mig2 protein is an import substrate of the carrier Kap95 (importin-β). The Mig2 nuclear import mechanism bypasses the requirement for Kap60 (importin-α) as an adaptor protein, since Mig2 directly binds to Kap95 in the presence of Gsp1(GDP). We also show that the Mig2 nuclear import and the binding of Mig2 with Kap95 are not glucose-dependent processes and require a basic NLS motif, located between lysine-32 and arginine-37. Mig2 interaction with Kap95 was assessed in vitro using purified proteins, demonstrating that importin-β, together with the GTP-binding protein Gsp1, is able to mediate efficient Mig2-Kap95 interaction in the absence of the importin-α (Kap60). It was also demonstrated, that the directionality of Mig2 transport is regulated by association with the small GTPase Gsp1 in the GDP- or GTP-bound forms, which promote cargo recognition and release, respectively.

Conclusions

The Mig2 protein accumulates in the nucleus through a Kap95 and NLS-dependent nuclear import pathway, which is independent of importin-α in Saccharomyces cerevisiae.

A 46,XY female DSD patient with bilateral gonadoblastoma, a novel SRY missense mutation combined with a WT1 KTS splice-site mutation

Patients with Disorders of Sex Development (DSD), especially those with gonadal dysgenesis and hypovirilization are at risk of developing malignant type II germ cell tumors/cancer (GCC) (seminoma/dysgerminoma and nonseminoma), with either carcinoma in situ (CIS) or gonadoblastoma (GB) as precursor lesion. In 10–15% of 46,XY gonadal dysgenesis cases (i.e., Swyer syndrome), SRY mutations, residing in the HMG (High Mobility Group) domain, are found to affect nuclear transport or binding to and bending of DNA. Frasier syndrome (FS) is characterized by gonadal dysgenesis with a high risk for development of GB as well as chronic renal failure in early adulthood, and is known to arise from a splice site mutation in intron 9 of the Wilms’ tumor 1 gene (WT1). Mutations in SRY as well as WT1 can lead to diminished expression and function of SRY, resulting in sub-optimal SOX9 expression, Sertoli cell formation and subsequent lack of proper testicular development. Embryonic germ cells residing in this unfavourable micro-environment have an increased risk for malignant transformation. Here a unique case of a phenotypically normal female (age 22 years) is reported, presenting with primary amenorrhoea, later diagnosed as hypergonadotropic hypogonadism on the basis of 46,XY gonadal dygenesis with a novel missense mutation in SRY. Functional in vitro studies showed no convincing protein malfunctioning. Laparoscopic examination revealed streak ovaries and a normal, but small, uterus. Pathological examination demonstrated bilateral GB and dysgerminoma, confirmed by immunohistochemistry. Occurrence of a delayed progressive kidney failure (focal segmental glomerular sclerosis) triggered analysis of WT1, revealing a pathogenic splice–site mutation in intron 9. Analysis of the SRY gene in an additional five FS cases did not reveal any mutations. The case presented shows the importance of multi-gene based diagnosis of DSD patients, allowing early diagnosis and treatment, thus preventing putative development of an invasive cancer.

The human testis-determining factor SRY localizes in midbrain dopamine neurons and regulates multiple components of catecholamine synthesis and metabolism

The male gender is determined by the sex-determining region on the Y chromosome (SRY) transcription factor. The unexpected action of SRY in the control of voluntary movement in male rodents suggests a role in the regulation of dopamine transmission and dopamine-related disorders with gender bias, such as Parkinson's disease. We investigated SRY expression in the human brain and function in vitro. SRY immunoreactivity was detected in the human male, but not female substantia nigra pars compacta, within a sub-population of tyrosine hydroxylase (TH) positive neurons. SRY protein also co-localized with TH positive neurons in the ventral tegmental area, and with GAD-positive neurons in the substantia nigra pars reticulata. Retinoic acid-induced differentiation of human precursor NT2 cells into dopaminergic cells increased expression of TH, NURR1, D2 R and SRY. In the human neuroblastoma cell line, M17, SRY knockdown resulted in a reduction in TH, DDC, DBH and MAO-A expression; enzymes which control dopamine synthesis and metabolism. Conversely, SRY over-expression increased TH, DDC, DBH, D2 R and MAO-A levels, accompanied by increased extracellular dopamine levels. A luciferase assay demonstrated that SRY activated a 4.6 kb 5' upstream regulatory region of the human TH promoter/nigral enhancer. Combined, these results suggest that SRY plays a role as a positive regulator of catecholamine synthesis and metabolism in the human male midbrain. This ancillary genetic mechanism might contribute to gender bias in fight-flight behaviours in men or their increased susceptibility to dopamine disorders, such as Parkinson's disease and schizophrenia.

Regulated nucleocytoplasmic transport during gametogenesis

Gametogenesis is the process by which sperm or ova are produced in the gonads. It is governed by a tightly controlled series of gene expression events, with some common and others distinct for males and females. Nucleocytoplasmic transport is of central importance to the fidelity of gene regulation that is required to achieve the precisely regulated germ cell differentiation essential for fertility. In this review we discuss the physiological importance for gamete formation of the molecules involved in classical nucleocytoplasmic protein transport, including importins/karyopherins, Ran and nucleoporins. To address what functions/factors are conserved or specialized for these developmental processes between species, we compare knowledge from mice, flies and worms. The present analysis provides evidence of the necessity for and specificity of each nuclear transport factor and for nucleoporins during germ cell differentiation. This article is part of a Special Issue entitled: Nuclear Transport and RNA Processing.

Distance and helical phase dependence of synergistic transcription activation in cis-regulatory module

Deciphering of the spatial and stereospecific constraints on synergistic transcription activation mediated between activators bound to cis-regulatory elements is important for understanding gene regulation and remains largely unknown. It has been commonly believed that two activators will activate transcription most effectively when they are bound on the same face of DNA double helix and within a boundary distance from the transcription initiation complex attached to the TATA box. In this work, we studied the spatial and stereospecific constraints on activation by multiple copies of bound model activators using a series of engineered relative distances and stereospecific orientations. We observed that multiple copies of the activators GAL4-VP16 and ZEBRA bound to engineered promoters activated transcription more effectively when bound on opposite faces of the DNA double helix. This phenomenon was not affected by the spatial relationship between the proximal activator and initiation complex. To explain these results, we proposed the novel concentration field model, which posits the effective concentration of bound activators, and therefore the transcription activation potential, is affected by their stereospecific positioning. These results could be used to understand synergistic transcription activation anew and to aid the development of predictive models for the identification of cis-regulatory elements.

Identification and functional analysis of SOX10 missense mutations in different subtypes of Waardenburg syndrome

Waardenburg syndrome (WS) is a rare disorder characterized by pigmentation defects and sensorineural deafness, classified into four clinical subtypes, WS1-S4. Whereas the absence of additional features characterizes WS2, association with Hirschsprung disease defines WS4. WS is genetically heterogeneous, with six genes already identified, including SOX10. About 50 heterozygous SOX10 mutations have been described in patients presenting with WS2 or WS4, with or without myelination defects of the peripheral and central nervous system (PCWH, Peripheral demyelinating neuropathy-Central dysmyelinating leukodystrophy-Waardenburg syndrome-Hirschsprung disease, or PCW, PCWH without HD). The majority are truncating mutations that most often remove the main functional domains of the protein. Only three missense mutations have been thus far reported. In the present study, novel SOX10 missense mutations were found in 11 patients and were examined for effects on SOX10 characteristics and functions. The mutations were associated with various phenotypes, ranging from WS2 to PCWH. All tested mutations were found to be deleterious. Some mutants presented with partial cytoplasmic redistribution, some lost their DNA-binding and/or transactivation capabilities on various tissue-specific target genes. Intriguingly, several mutants were redistributed in nuclear foci. Whether this phenomenon is a cause or a consequence of mutation-associated pathogenicity remains to be determined, but this observation could help to identify new SOX10 modes of action.

Mammalian testis-determining factor SRY and the enigma of inherited human sex reversal: frustrated induced fit in a bent protein-DNA complex

Mammalian testis-determining factor SRY contains a high mobility group box, a conserved eukaryotic motif of DNA bending. Mutations in SRY cause XY gonadal dysgenesis and somatic sex reversal. Although such mutations usually arise de novo in spermatogenesis, some are inherited and so specify male development in one genetic background (the father) but not another (the daughter). Here, we describe the biophysical properties of a representative inherited mutation, V60L, within the minor wing of the L-shaped domain (box position 5). Although the stability and DNA binding properties of the mutant domain are similar to those of wild type, studies of SRY-induced DNA bending by subnanosecond time-resolved fluorescence resonance energy transfer (FRET) revealed enhanced conformational fluctuations leading to long range variation in bend angle. (1)H NMR studies of the variant protein-DNA complex demonstrated only local perturbations near the mutation site. Because the minor wing of SRY folds on DNA binding, the inherited mutation presumably hinders induced fit. Stopped-flow FRET studies indicated that such frustrated packing leads to accelerated dissociation of the bent complex. Studies of SRY-directed transcriptional regulation in an embryonic gonadal cell line demonstrated partial activation of downstream target Sox9. Our results have demonstrated a nonlocal coupling between DNA-directed protein folding and protein-directed DNA bending. Perturbation of this coupling is associated with a genetic switch poised at the threshold of activity.

Regulation of Nuclear Import During Differentiation; The IMP alpha Gene Family and Spermatogenesis

Access to nuclear genes in eukaryotes is provided by members of the importin (IMP) superfamily of proteins, which are of α- or β-types, the best understood nuclear import pathway being mediated by a heterodimer of an IMP α and IMP β1. IMP α recognises specific targeting signals on cargo proteins, while IMP β1 mediates passage into, and release within, the nucleus by interacting with other components of the transport machinery, including the monomeric guanine nucleotide binding protein Ran. In this manner, hundreds of different proteins can be targeted specifically into the nucleus in a tightly regulated fashion. The IMP α gene family has expanded during evolution, with only a single IMP α (Srp1p) gene in budding yeast, and three (IMP α1, 2/pendulin and 3) and five (IMP α1, -2, -3, -4 and -6) IMP α genes in Drosophila melanogaster and mouse respectively, which fall into three phylogenetically distinct groups. The fact that IMP α3 and IMP α2 are only present in metazoans implies that they emerged during the evolution of multicellular animals to perform specialised roles in particular cells and tissues. This review describes what is known of the IMP α gene family in mouse and in D. melanogaster, including a comparitive examination of their mRNA expression profiles in a highly differentiated tissue, the testis. The clear implication of their highly regulated synthesis during the course of spermatogenesis is that the different IMP αs have distinct expression patterns during cellular differentiation, implying tissue/cell type-specific roles.

Inhibition of SRY-calmodulin complex formation induces ectopic expression of ovarian cell markers in developing XY gonads

The transcription factor sex-determining region of the Y chromosome (SRY) plays a key role in human sex determination, because mutations in SRY cause disorders of sex development in XY individuals. During gonadal development, Sry in pre-Sertoli cells activates Sox9 gene transcription, committing the fate of the bipotential gonad to become a testis rather than an ovary. The high-mobility group domain of human SRY contains two independent nuclear localization signals, one bound by calmodulin (CaM) and the other by importin-β. Although XY females carry SRY mutations in these nuclear localization signals that affect SRY nuclear import in transfected cells, it is not known whether these transport mechanisms are essential for gonadal development and sex determination. Here, we show that mouse Sry protein binds CaM and that a CaM antagonist reduces CaM binding, nuclear accumulation, and transcriptional activity of Sry in transfected cells. CaM antagonist treatment of cultured, sexually indifferent XY mouse fetal gonads led to reduced expression of the Sry target gene Sox9, defects in testicular cord formation, and ectopic expression of the ovarian markers Rspondin1 and forkhead box L2. These results indicate the importance of CaM for SRY nuclear import, transcriptional activity, testis differentiation, and sex determination.

Sry, more than testis determination?

The Sry locus on the mammalian Y chromosome is the developmental switch responsible for testis determination. Inconsistent with this important function, the Sry locus is transcribed in adult males at times and in tissues not involved with testis determination. Sry is expressed in multiple tissues of the peripheral and central nervous system. Sry is derived from Sox3 and is similar to other SOXB family loci. The SOXB loci are responsible for nervous system development. Sry has been demonstrated to modulate the catecholamine pathway, so it should have functional consequences in the central and peripheral nervous system. The nervous system expression and potential function are consistent with Sry as a SOXB family member. In mammals, Sox3 is X-linked and undergoes dosage compensation in females. The expression of Sry in adult males allows for a type of sexual differentiation independent of circulating gonadal hormones. A quantitative difference in Sox3 plus Sry expression in males vs. females could drive changes in the transcriptome of these cells, differentiating male and female cells. Sry expression and its transcriptional effects should be considered when investigating sexual dimorphic phenotypes.