Turning on the male – SRY, SOX9 and sex determination in mammals

Reprograming skin fibroblasts into Sertoli cells: a patient-specific tool to understand effects of genetic variants on gonadal development

BACKGROUND

Disorders/differences of sex development (DSD) are congenital conditions in which the development of chromosomal, gonadal, or anatomical sex is atypical. With overlapping phenotypes and multiple genes involved, poor diagnostic yields are achieved for many of these conditions. The current DSD diagnostic regimen can be augmented by investigating transcriptome/proteome in vivo, but it is hampered by the unavailability of affected gonadal tissue at the relevant developmental stage. We try to mitigate this limitation by reprogramming readily available skin tissue-derived dermal fibroblasts into Sertoli cells (SC), which could then be deployed for different diagnostic strategies. SCs form the target cell type of choice because they act like an organizing center of embryonic gonadal development and many DSD arise when these developmental processes go awry.

METHODS

We employed a computational predictive algorithm for cell conversions called Mogrify to predict the transcription factors (TFs) required for direct reprogramming of human dermal fibroblasts into SCs. We established trans-differentiation culture conditions where stable transgenic expression of these TFs was achieved in 46, XY adult dermal fibroblasts using lentiviral vectors. The resulting Sertoli like cells (SLCs) were validated for SC phenotype using several approaches.

RESULTS

SLCs exhibited Sertoli-like morphological and cellular properties as revealed by morphometry and xCelligence cell behavior assays. They also showed Sertoli-specific expression of molecular markers such as SOX9, PTGDS, BMP4, or DMRT1 as revealed by IF imaging, RNAseq and qPCR. The SLC transcriptome shared about two thirds of its differentially expressed genes with a human adult SC transcriptome and expressed markers typical of embryonic SCs. Notably, SLCs lacked expression of most markers of other gonadal cell types such as Leydig, germ, peritubular myoid or granulosa cells.

CONCLUSIONS

The trans-differentiation method was applied to a variety of commercially available 46, XY fibroblasts derived from patients with DSD and to a 46, XX cell line. The DSD SLCs displayed altered levels of trans-differentiation in comparison to normal 46, XY-derived SLCs, thus showcasing the robustness of this new trans-differentiation model. Future applications could include using the SLCs to improve definitive diagnosis of DSD in patients with variants of unknown significance.

Gene expression of male pathway genes sox9 and amh during early sex differentiation in a reptile departs from the classical amniote model

BACKGROUND

Sex determination is the process whereby the bipotential embryonic gonads become committed to differentiate into testes or ovaries. In genetic sex determination (GSD), the sex determining trigger is encoded by a gene on the sex chromosomes, which activates a network of downstream genes; in mammals these include SOX9, AMH and DMRT1 in the male pathway, and FOXL2 in the female pathway. Although mammalian and avian GSD systems have been well studied, few data are available for reptilian GSD systems.

RESULTS

We conducted an unbiased transcriptome-wide analysis of gonad development throughout differentiation in central bearded dragon (Pogona vitticeps) embryos with GSD. We found that sex differentiation of transcriptomic profiles occurs at a very early stage, before the gonad consolidates as a body distinct from the gonad-kidney complex. The male pathway genes dmrt1 and amh and the female pathway gene foxl2 play a key role in early sex differentiation in P. vitticeps, but the central player of the mammalian male trajectory, sox9, is not differentially expressed in P. vitticeps at the bipotential stage. The most striking difference from GSD systems of other amniotes is the high expression of the male pathway genes amh and sox9 in female gonads during development. We propose that a default male trajectory progresses if not repressed by a W-linked dominant gene that tips the balance of gene expression towards the female trajectory. Further, weighted gene expression correlation network analysis revealed novel candidates for male and female sex differentiation.

CONCLUSION

Our data reveal that interpretation of putative mechanisms of GSD in reptiles cannot solely depend on lessons drawn from mammals.

Mebendazole-Induced Blood-Testis Barrier Injury in Mice Testes by Disrupting Microtubules in Addition to Triggering Programmed Cell Death

Mebendazole (MBZ) is a synthetic benzimidazole known for its antiparasitic properties. In recent years, growing evidence showed that MBZ was also used as an anti-tumor agent. However, whether (and to what extent) this drug treatment affected the male reproductive system was not well-understood. In this study, male C57BL/6 mice were injected with 40 mg/kg/day of MBZ. The treatment was for 3 and 7 days. Our results showed that the injected mice exhibited an abnormal spermatogenic phase with a significant decrease in sperm. We further detected microtubule disruption and transient functional destruction of the blood–testes barrier (BTB) in the MBZ-injected mice testes (BTB). Our data confirmed that MBZ suppressed the expression of the BTB junction-associated proteins and disrupted the Sertoli cells’ function in vivo. Moreover, MBZ-treated mice demonstrated an aberrant caspase-3 signalling pathway, which resulted in the apoptosis of the germ cells. Here, we present our data, indicating that MBZ impairs BTB by reducing the expression of the microtubules’ and BTB junction-associated proteins. The last leads to activating the caspase-3 pathway, which triggers extensive germ cell apoptosis.

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.

Non-Coding Genome, Transcription Factors, and Sex Determination

In vertebrates, gonadal sex determination is the process by which transcription factors drive the choice between the testicular and ovarian identity of undifferentiated somatic progenitors through activation of 2 different transcriptional programs. Studies in animal models suggest that sex determination always involves sex-specific transcription factors that activate or repress sex-specific genes. These transcription factors control their target genes by recognizing their regulatory elements in the non-coding genome and their binding motifs within their DNA sequence. In the last 20 years, the development of genomic approaches that allow identifying all the genomic targets of a transcription factor in eukaryotic cells gave the opportunity to globally understand the function of the nuclear proteins that control complex genetic programs. Here, the major transcription factors involved in male and female vertebrate sex determination and the genomic profiling data of mouse gonads that contributed to deciphering their transcriptional regulation role will be reviewed.

Oestrogen regulates SOX9 bioavailability by rapidly activating ERK1/2 and stabilising microtubules in a human testis-derived cell line

Nuclear SOX9 is essential for Sertoli cell differentiation and the development of a testis. Exposure of Sertoli cells to exogenous oestrogen causes cytoplasmic retention of SOX9, inhibiting testis development and promoting ovarian development. The cytoplasmic localisation of SOX9 requires a stabilised microtubule network and a key MAPK complex, ERK1/2, is responsive to oestrogen and known to affect the microtubule network. We hypothesised that oestrogen could stabilise microtubules through the activation of ERK1/2 to promote the cytoplasmic retention of SOX9. Treatment of human testis-derived NT2/D1 cells for 30 min with oestrogen rapidly activated ERK1/2, stabilised the microtubule network and increased cytoplasmic localisation of SOX9. The effects of oestrogen on SOX9 and tubulin were blocked by the ERK1/2 inhibitor U0126, demonstrating that ERK1/2 mediates the stabilisation of microtubules and cytoplasmic retention of SOX9 by oestrogen. Together, these data revealed a previously unknown mechanism for oestrogen in impacting MAPK signalling to block SOX9 bioavailability and the differentiation of Sertoli cells.

Estrogen suppresses SOX9 and activates markers of female development in a human testis-derived cell line

Background

The increasing incidence of reproductive disorders in humans has been attributed to in utero exposure to estrogenic endocrine disruptors. In particular, exposure of the developing testis to exogenous estrogen can negatively impact male reproductive health. To determine how estrogens impact human gonad function, we treated the human testis-derived cell line NT2/D1 with estrogen and examined its impact on SOX9 and the expression of key markers of granulosa (ovarian) and Sertoli (testicular) cell development.

Results

Estrogen successfully activated its cognate receptor (estrogen receptor alpha; ESR1) in NT2/D1 cells. We observed a significant increase in cytoplasmic SOX9 following estrogen treatment. After 48 h of estrogen exposure, mRNA levels of the key Sertoli cell genes SOX9, SRY, AMH, FGF9 and PTGDS were significantly reduced. This was followed by a significant increase in mRNA levels for the key granulosa cell genes FOXL2 and WNT4 after 96 h of estrogen exposure.

Conclusions

These results are consistent with estrogen's effects on marsupial gonads and show that estrogen has a highly conserved impact on gonadal cell fate decisions that has existed in mammals for over 160 million years. This effect of estrogen presents as a potential mechanism contributing to the significant decrease in male fertility and reproductive health reported over recent decades. Given our widespread exposure to estrogenic endocrine disruptors, their effects on SOX9 and Sertoli cell determination could have considerable impact on the adult testis.

Pig SOX9: Expression profiles of Sertoli cell (SCs) and a functional 18 bp indel affecting testis weight

Sex determining region Y-box 9 (SOX9), an important member of the SRY- type HMGbox (SOX) gene family, plays an important role in the regulation of mammalian reproduction, including sex differentiation during the embryonic development stage and spermatogenesis after birth. To explore the roles of polymorphism and expression of the SOX9 gene in the development of testes, we analyzed the indel of SOX9 in pigs and the corresponding expression level of the SOX9 gene in 7-day and 5-month-old porcine Sertoli cells. Results revealed that the DD haplotype of SOX9 gene as well as the ID genotype were significantly associated with larger testicular weight, while the II haplotype was closely related to the smaller testicular weight. More importantly, the SOX9 gene expression of ID genotyped group was significantly higher than that in II genotyped group. Our results first revealed that the indel polymorphism and expression of SOX9 were significantly associated with pig reproduction traits indicating the critical roles of SOX9 gene in testes development. The study provides a new clue for understanding the regulation of animal reproductive activities.

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.

The biology of germ cell tumors in disorders of sex development

Development of a malignant germ cell tumor, i.e., germ cell cancer (GCC) in individuals with disorders of sex development (DSD) depends on a number of (epi-)genetic factors related to early gonadal- and germ cell development, possibly related to genetic susceptibility. Fetal development of germ cells is orchestrated by strict processes involving specification, migration and the development of a proper gonadal niche. In this review we will discuss the early (epi-)genetic events in normal and aberrant germ cell and gonadal development. Focus will be on the formation of the precursor lesions of GCC in individuals who have DSD. In our view, expression of the different embryonic markers in, and epigenetic profile of the precursor lesions reflects the developmental stage in which these cells are blocked in their maturation. Therefore, these are not a primary pathogenetic driving force. Progression later in life towards a full blown cancer likely depends on additional factors such as a changed endocrine environment in a susceptible individual. Genetic susceptibility is, as evidenced by the presence of specific risk genetic variants (SNPs) in patients with a testicular GCC, related to genes involved in early germ cell and gonadal development.

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.

Gene expression analysis at the onset of sex differentiation in turbot (Scophthalmus maximus)

BACKGROUND

Controlling sex ratios is essential for the aquaculture industry, especially in those species with sex dimorphism for relevant productive traits, hence the importance of knowing how the sexual phenotype is established in fish. Turbot, a very important fish for the aquaculture industry in Europe, shows one of the largest sexual growth dimorphisms amongst marine cultured species, being all-female stocks a desirable goal for the industry. Although important knowledge has been achieved on the genetic basis of sex determination (SD) in this species, the master SD gene remains unknown and precise information on gene expression at the critical stage of sex differentiation is lacking. In the present work, we examined the expression profiles of 29 relevant genes related to sex differentiation, from 60 up to 135 days post fertilization (dpf), when gonads are differentiating. We also considered the influence of three temperature regimes on sex differentiation.

RESULTS

The first sex-related differences in molecular markers could be observed at 90 days post fertilization (dpf) and so we have called that time the onset of sex differentiation. Three genes were the first to show differential expression between males and females and also allowed us to sex turbot accurately at the onset of sex differentiation (90 dpf): cyp19a1a, amh and vasa. The expression of genes related to primordial germ cells (vasa, gsdf, tdrd1) started to increase between 75-90 dpf and vasa and tdrd1 later presented higher expression in females (90-105 dpf). Two genes placed on the SD region of turbot (sox2, fxr1) did not show any expression pattern suggestive of a sex determining function. We also detected changes in the expression levels of several genes (ctnnb1, cyp11a, dmrt2 or sox6) depending on culture temperature.

CONCLUSION

Our results enabled us to identify the first sex-associated genetic cues (cyp19a1a, vasa and amh) at the initial stages of gonad development in turbot (90 dpf) and to accurately sex turbot at this age, establishing the correspondence between gene expression profiles and histological sex. Furthermore, we profiled several genes involved in sex differentiation and found specific temperature effects on their expression.

Porcine SOX9 Gene Expression Is Influenced by an 18 bp Indel in the 5'-Untranslated Region

Sex determining region Y-box 9 (SOX9) is an important regulator of sex and skeletal development and is expressed in a variety of embryonal and adult tissues. Loss or gain of function resulting from mutations within the coding region or chromosomal aberrations of the SOX9 locus lead to a plethora of detrimental phenotypes in humans and animals. One of these phenotypes is the so-called male-to-female or female-to-male sex-reversal which has been observed in several mammals including pig, dog, cat, goat, horse, and deer. In 38,XX sex-reversal French Large White pigs, a genome-wide association study suggested SOX9 as the causal gene, although no functional mutations were identified in affected animals. However, besides others an 18bp indel had been detected in the 5′-untranslated region of the SOX9 gene by comparing affected animals and controls. We have identified the same indel (Δ18) between position +247bp and +266bp downstream the transcription start site of the porcine SOX9 gene in four other pig breeds; i.e., German Large White, Laiwu Black, Bamei, and Erhualian. These animals have been genotyped in an attempt to identify candidate genes for porcine inguinal and/or scrotal hernia. Because the 18bp segment in the wild type 5′-UTR harbours a highly conserved cAMP-response element (CRE) half-site, we analysed its role in SOX9 expression in vitro. Competition and immunodepletion electromobility shift assays demonstrate that the CRE half-site is specifically recognized by CREB. Both binding of CREB to the wild type as well as the absence of the CRE half-site in Δ18 reduced expression efficiency in HEK293T, PK–15, and ATDC5 cells significantly. Transfection experiments of wild type and Δ18 SOX9 promoter luciferase constructs show a significant reduction of RNA and protein levels depending on the presence or absence of the 18bp segment. Hence, the data presented here demonstrate that the 18bp indel in the porcine SOX9 5′-UTR is of functional importance and may therefore indeed be a causative variation in SOX9 associated traits.

A multi-faceted approach to understanding male infertility: gene mutations, molecular defects and assisted reproductive techniques (ART)

BACKGROUND

The assisted reproductive techniques aimed to assist infertile couples have their own offspring carry significant risks of passing on molecular defects to next generations.

RESULTS

Novel breakthroughs in gene and protein interactions have been achieved in the field of male infertility using genome-wide proteomics and transcriptomics technologies.

CONCLUSION

Male Infertility is a complex and multifactorial disorder.

SIGNIFICANCE

This review provides a comprehensive, up-to-date evaluation of the multifactorial factors involved in male infertility. These factors need to be first assessed and understood before we can successfully treat male infertility.

Upregulation of SOX9 in osteosarcoma and its association with tumor progression and patients' prognosis

Objective

SOX9 plays an important role in bone formation and tumorigenesis. However, its involvement in osteosarcoma is still unclear. The aim of this study was to investigate the expression pattern and the clinical significance of SOX9 in human osteosarcoma.

Methods

SOX9 mRNA and protein expression levels were detected by RT-PCR and Western blot assays, respectively, using 30 pairs of osteosarcoma and noncancerous bone tissues. Then, immunohistochemistry was performed to analyze the association of SOX9 expression in 166 osteosarcoma tissues with clinicopathological factors or survival of patients.

Results

SOX9 expression at mRNA and protein levels were both significantly higher in osteosarcoma tissues than those in corresponding noncancerous bone tissues (both P < 0.001). Immunohistochemical staining indicated that SOX9 localized to the nucleus and high SOX9 expression was observed in 120 of 166 (72.3%) osteosarcoma specimens. In addition, high SOX9 expression was more frequently occurred in osteosarcoma tissues with advanced clinical stage (P = 0.02), positive distant metastasis (P = 0.008) and poor response to chemotherapy (P = 0.02). Osteosarcoma patients with high SOX9 expression had shorter overall survival and disease-free survival (both P < 0.001). Furthermore, the multivariate analysis confirmed that upregulation of SOX9 was an independent and significant prognostic factor to predict poor overall survival and disease-free survival (both P = 0.006).

Conclusions

Our data show for the first time that SOX9 is upregulated in aggressive osteosarcoma tissues indicating that SOX9 may participate in the osteosarcoma progression. More importantly, SOX9 status is a useful prognostic factor for predicting the prognosis of osteosarcoma, suggesting that SOX9 may contribute to the optimization of clinical treatments for osteosarcoma patients.

Virtual slides

The virtual slides for this article can be found here: http://www.diagnosticpathology.diagnomx.eu/vs/1318085636110837.

Inherited human sex reversal due to impaired nucleocytoplasmic trafficking of SRY defines a male transcriptional threshold

Human testis determination is initiated by SRY (sex determining region on Y chromosome). Mutations in SRY cause gonadal dysgenesis with female somatic phenotype. Two subtle variants (V60L and I90M in the high-mobility group box) define inherited alleles shared by an XY sterile daughter and fertile father. Whereas specific DNA binding and bending are unaffected in a rat embryonic pre-Sertoli cell line, the variants exhibited selective defects in nucleocytoplasmic shuttling due to impaired nuclear import (V60L; mediated by Exportin-4) or export (I90M; mediated by chromosome region maintenance 1). Decreased shuttling limits nuclear accumulation of phosphorylated (activated) SRY, in turn reducing occupancy of DNA sites regulating Sertoli-cell differentiation [the testis-specific SRY-box 9 (Sox9) enhancer]. Despite distinct patterns of biochemical and cell-biological perturbations, V60L and I90M each attenuated Sox9 expression in transient transfection assays by twofold. Such attenuation was also observed in studies of V60A, a clinical variant associated with ovotestes and hence ambiguity between divergent cell fates. This shared twofold threshold is reminiscent of autosomal syndromes of transcription-factor haploinsufficiency, including XY sex reversal associated with mutations in SOX9. Our results demonstrate that nucleocytoplasmic shuttling of SRY is necessary for robust initiation of testicular development. Although also characteristic of ungulate orthologs, such shuttling is not conserved among rodents wherein impaired nuclear export of the high-mobility group box and import-dependent phosphorylation are compensated by a microsatellite-associated transcriptional activation domain. Human sex reversal due to subtle defects in the nucleocytoplasmic shuttling of SRY suggests that its transcriptional activity lies near the edge of developmental ambiguity.

A network of HMG-box transcription factors regulates sexual cycle in the fungus Podospora anserina

High-mobility group (HMG) B proteins are eukaryotic DNA-binding proteins characterized by the HMG-box functional motif. These transcription factors play a pivotal role in global genomic functions and in the control of genes involved in specific developmental or metabolic pathways. The filamentous ascomycete Podospora anserina contains 12 HMG-box genes. Of these, four have been previously characterized; three are mating-type genes that control fertilization and development of the fruit-body, whereas the last one encodes a factor involved in mitochondrial DNA stability. Systematic deletion analysis of the eight remaining uncharacterized HMG-box genes indicated that none were essential for viability, but that seven were involved in the sexual cycle. Two HMG-box genes display striking features. PaHMG5, an ortholog of SpSte11 from Schizosaccharomyces pombe, is a pivotal activator of mating-type genes in P. anserina, whereas PaHMG9 is a repressor of several phenomena specific to the stationary phase, most notably hyphal anastomoses. Transcriptional analyses of HMG-box genes in HMG-box deletion strains indicated that PaHMG5 is at the hub of a network of several HMG-box factors that regulate mating-type genes and mating-type target genes. Genetic analyses revealed that this network also controls fertility genes that are not regulated by mating-type transcription factors. This study points to the critical role of HMG-box members in sexual reproduction in fungi, as 11 out of 12 members were involved in the sexual cycle in P. anserina. PaHMG5 and SpSte11 are conserved transcriptional regulators of mating-type genes, although P. anserina and S. pombe diverged 550 million years ago. Two HMG-box genes, SOX9 and its upstream regulator SRY, also play an important role in sex determination in mammals. The P. anserina and S. pombe mating-type genes and their upstream regulatory factor form a module of HMG-box genes analogous to the SRY/SOX9 module, revealing a commonality of sex regulation in animals and fungi.

Podospora anserina, a coprophilous fungus, is used extensively as a model organism to address questions of sexual development and mating-type functions. Its mating-type locus contains three HMGB genes that encode transcription factors involved in fertilization and fruit-body development. We present the functional characterization of the remaining HMGB genes, which revealed that 11 of 12 HMGB genes were involved in sexual development. An analysis of the relationships between these genes uncovered a regulatory network governing the expression of mating-type genes. PaHMG5 is a key transcription factor that operates upstream of mating-type genes in this network. A homolog of PaHMG5 performs a similar function in the fission yeast Schizosaccharomyces pombe, which diverged from P. anserina 550 million years ago. The conservation of a regulatory circuit over such a prolonged timeframe is a striking exception to the general observation that sex developmental pathways are highly variable, even across closely related lineages. A module consisting of two HMGB transcription factors (Sry and Sox9) is a key regulator of sex determination in mammals. We propose that the module containing PaHMG5 and mating-type HMGB genes is the fungal counterpart of the mammalian module, revealing a commonality of sex regulation in animals and fungi.

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.

Molecular mechanisms of sexual development

Gonadal cellular organization is very similar in all vertebrates, though different processes can trigger bipotential gonads to develop into either testes or ovaries. While mammals and birds, apart from some exceptions, show genetic sex determination (GSD), other animals, like turtles and crocodiles, express temperature-dependent sex determination. In some groups of animals, GSD can also be overridden by hormone or temperature influences, indicating how fragile this system can be. This review aims to explain the fundamental molecular mechanisms involved in mammalian GSD, mainly referring to mouse as a major model. Conceivably, other mammals might show a molecular mechanism different from the commonly investigated murine species.

Novel DMRT1 3'UTR+11insT mutation associated to XY partial gonadal dysgenesis

The Y-chromosome-located SRY gene encodes a small testis-specific protein containing a DNA-binding motif known as the HMG (high mobility group) box. However, mutations in SRY are not frequent especially in cases of 46,XY partial gonadal dysgenesis. Several sex-determining genes direct the fate of the bipotential gonad to either testis or ovary. In addition, heterozygous small deletions in 9p can cause complete and partial XY gonadal dysgenesis without other symptoms. Human DMRT1 gene, which is located at 9p24.3, is expressed in testis and ovary and has been considered, among others, a candidate autosomal gene responsible for gonadal dysgenesis. In this report we describe a nucleotide insertion in DMRT1 3'UTR in a patient of XY partial gonadal dygenesis. The 3'UTR+11insT is located within a conserved motif important for mRNA stabilization.

Calmodulin-dependent nuclear import of HMG-box family nuclear factors: importance of the role of SRY in sex reversal

The HMG (high-mobility group)-box-containing chromatin-remodelling factor SRY (sex-determining region on the Y chromosome) plays a key role in sex determination. Its role in the nucleus is critically dependent on two NLSs (nuclear localization signals) that flank its HMG domain: the C-terminally located 'beta-NLS' that mediates nuclear transport through Impbeta1 (importin beta1) and the N-terminally located 'CaM-NLS' which is known to recognize the calcium-binding protein CaM (calmodulin). In the present study, we examined a number of missense mutations in the SRY CaM-NLS from human XY sex-reversed females for the first time, showing that they result in significantly reduced nuclear localization of GFP (green fluorescent protein)-SRY fusion proteins in transfected cells compared with wild-type. The CaM antagonist CDZ (calmidazolium chloride) was found to significantly reduce wild-type SRY nuclear accumulation, indicating dependence of SRY nuclear import on CaM. Intriguingly, the CaM-NLS mutants were all resistant to CDZ's effects, implying a loss of interaction with CaM, which was confirmed by direct binding experiments. CaM-binding/resultant nuclear accumulation was the only property of SRY found to be impaired by two of the CaM-NLS mutations, implying that inhibition of CaM-dependent nuclear import is the basis of sex reversal in these cases. Importantly, the CaM-NLS is conserved in other HMG-box-domain-containing proteins such as SOX-2, -9, -10 and HMGN1, all of which were found for the first time to rely on CaM for optimal nuclear localization. CaM-dependent nuclear translocation is thus a common mechanism for this family of important transcription factors.

Testis development, fertility, and survival in Ethanolamine kinase 2-deficient mice

Ethanolamine kinase 2 (Eki2) was previously isolated from a differential expression screen designed to identify candidate genes involved in testis development and differentiation. In mouse, Eki2 is specifically up-regulated in Sertoli cells of the developing testis at the time of sex determination. Based on this expression profile, Eki2 was considered a good candidate testis-determining gene. To investigate a possible role of Eki2 in testis development, we have generated a mouse with targeted disruption of the Eki2 gene by using an EGFP replacement strategy. No abnormalities were detected in the Eki2-deficient mice with regard to embryonic and adult testis morphology, differentiation, function, or fertility. Furthermore, no significant differences were observed in litter sizes, pup mortality rates, or distribution of the sexes among the offspring. Ethanolamine kinases are involved in the biosynthesis of phosphatidylethanolamine, a major membrane phospholipid. Expression analysis indicates that the absence of an apparent phenotype in the Eki2-deficient mice may be due to compensation by Eki2-family members or the activation of an alternative pathway to generate phosphatidylethanolamine. Expression of EGFP in this mouse model enabled the isolation of gonad cell populations, providing a useful resource from which to obtain relatively pure early steroidogenic cells for further studies.

Boys, girls and shuttling of SRY and SOX9

In the mammalian embryo, SRY and SOX9 are key Sertoli cell proteins that drive the development of the bipotential gonad into a testes rather than an ovary, leading ultimately to the male phenotype. Clinical SRY and SOX9 mutations causing disorders of sex development (DSD) highlight defective protein-protein interactions between SRY or SOX9, and carrier proteins required for nuclear import (importin-b and calmodulin) and nuclear export (CRM-1). The fine balance between import and export determines the levels of transcriptionally active SRY and SOX9 in the nucleus. Recently, post-translational modifications of SRY and SOX9 have been identified which affect nuclear transport. It is therefore timely that the consequences of sex-reversal mutation upon nuclear transport be reviewed. SRY and SOX9 mutations in DSD have uncovered regulatory sites for sumoylation, ubiquitination, acetylation and phosphorylation, many of which are essential for their transport and sex determining functions.

[A Case of 46,XY pure gonadal dysgenesis with loss of the sex-determining region of Y chromosome]

A 23-yr-old phenotypic female was seen for primary amenorrhea. Her pubic hair was relatively well developed and external genitalia showed normal female appearance, but breast development was retarded. Transvaginal ultrasonographic examination showed a small uterus with indistinct streak gonads, but both ovaries were not detected. Cytogenetic study revealed 46,XY. In FISH and PCR, the sex-determining region of Y chromosome (SRY) was not detected. We report here a case of 46,XY pure gonadal dysgenesis with loss of the SRY.

Cloning and study of adult-tissue-specific expression of Sox9 in Cyprinus carpio

The Sox9 gene is one of the important transcription factors in the development of many tissues and organs, particularly in sex determination and chondrogenesis. We amplified the genomic DNA of Cyprinus carpio using degenerate primers, and found that there were two versions of Sox9 in this species: Sox9a and Sox9b, that differ in having an intron of different length (704 bp and 616 bp, respectively) in the conserved HMG box region that codes for identical amino acid sequences. We used a two-phase rapid amplification of cDNA ends (RACE) for the isolation of full-length cDNA of Sox9b. Sequence analyses revealed a 2447-bp cDNA containing 233-bp 5' untranslated region, a 927-bp 3' untranslated region, including poly(A), and a 1287 bp open reading frame (ORF) encoding a protein of 428 amino acids. The HMG box of 79 amino acid motif was confirmed from positions 96-174. Sequence alignment showed that the identity of amino acids of Sox9 among ten animal species, including C. carpio, is 75%, indicating that the Sox9 gene is evolutionarily quite conserved. The expression level of Sox9b gene varied among several organs of adult C. carpio, with the level of expression being highest in the brain and testis.

Identification and molecular modelling of a novel familial mutation in the SRY gene implicated in the pure gonadal dysgenesis

SRY gene is responsible for initiating male sexual differentiation. The protein encoded by SRY contains a homeobox (HMG) domain, which is a DNA-binding domain. Mutations of the SRY gene are reported to be associated with XY pure gonadal dysgenesis. The majority of these are de novo mutations affecting only one individual in a family. Only a small subset of mutations is shared between the father and one or more of his children. Most of these familial mutations are localized within the HMG box and only two are at the N-terminal domain of the SRY protein. Herein, we describe a young girl with pure gonadal dysgenesis and her father carrying a novel familial mutation in the SRY gene at codon number 3. This mutation is resulting in a serine (S) to leucine (L) substitution. The secondary structure of the SRY protein was carried out by protein modelling studies. This analysis suggests, with high possibility, that the N-terminal domain of the SRY protein, where we found the mutation, could form an alpha-helix from amino acid in position 2 to amino acid in position 13. The secondary structure prediction and the chemical properties of serine to leucine substitution stands for a potential disruption of this N-terminal alpha-helix in the SRY protein. This mutation could have some role in impeding the normal function of the SRY protein.

Comparative phylogenetics offer new insights into the biogeographic history of Macaca fascicularis and the origin of the Mauritian macaques

We employ a comparative phylogenetic analysis to gain insight into the recent evolutionary history of Macaca fascicularis, the long-tailed macaque. Mitochondrial and Y-chromosomal topologies both show that, in general, the deepest intraspecific bifurcations separate Indochinese and Sundaic forms of this species. Sumatran populations, however, are an exception: they carry one Y-chromosomal lineage that clusters with continental populations, and another that clusters with insular stocks. This discovery provides insight into two events in the history of M. fascicularis. First, the presence of the 'continental' Y-lineage on Sumatra is one of the strongest lines of evidence to date for recent (Late Pleistocene) gene flow between Indochinese and Sundaic populations. Second, since Sumatra is the only region known to carry 'continental' YDNA and 'insular' mtDNA, it is considered the most likely source of the Mauritian macaques-an important biomedical research stock that appears to carry this mtDNA/YDNA combination exclusively.

Mouse models for genes involved in impaired spermatogenesis

Since the introduction of molecular biology and gene ablation technologies there have been substantial advances in our understanding of how sperm are made and fertilization occurs. There have been at least 150 different models of specifically altered gene function produced that have resulted in male infertility spanning virtually all aspects of the spermatogenic, sperm maturation and fertilization processes. While each has, or potentially will reveal, novel aspects of these processes, there is still much of which we have little knowledge. The current review is by no means a comprehensive list of these mouse models, rather it gives an overview of the potential for such models which up to this point have generally been 'knockouts'; it presents alternative strategies for the production of new models and emphasizes the importance of thorough phenotypic analysis in order to extract a maximum amount of information from each model.

Novel SOX9 Gene Mutation in Campomelic Dysplasia with Autosomal Sex Reversal

Campomelic dysplasia (CD; OMIM #114290) is an autosomal dominant, frequently lethal dysplasia syndrome whose primary features include angular bowing and shortening of the limbs, and sex reversal in the majority of affected XY individuals. Most CD cases have heterozygous de novo mutations in the coding region of the transcription factor gene SOX9 (SRY-related high-mobility group [HMG] box 9) in chromosome 17q. Here, we report a novel mutation of SOX9 in a female neonate with CD with autosomal sex reversal. Respiratory distress and cyanosis were noted at birth, and endotracheal intubation with mechanical ventilation was performed due to respiratory failure. The presenting phenotypes included dysmorphic face with macrocephaly, prominent forehead, low nasal bridge, cleft palate and micrognathia. Skeletal deformities characteristic of CD were observed, including narrow thoracic cage, hypoplastic scapulae, scoliosis and short limbs with anterolateral femoral and tibial bowing. The karyotype was 46,XY despite female external genitalia. SOX9 gene analysis revealed frameshift mutation (at nucleotide position 1095G-->AT) in the open reading frame, resulting in a frameshift with 211 new amino acids.

Design of Hammerhead Ribozymes that Cleave Murine Sry mRNA In Vitro and In Vivo

As the first step in investigating the possiblity of applying ribozyme technology to artificial control of the sex ratios at birth in farm animals, where the demand for females exceeds that for males, we designed a hammerhead ribozyme (HHRz) and 2 tRNA(val)-hammerhead ribozyme complexes (tRNARz3 and tRNARz4), and examined their effects upon murine Sry mRNA in vitro and in cells. We demonstrated that HHRz and tRNARz3 could effectively cleave the target Sry mRNA in vitro. For the purpose of experiments in vivo, HHRz was cloned into the highly efficient pUC-CAGGS mammalian expression vector (pCAG/HHRz), and the tRNA ribozyme complexes were cloned into the pol III promoter-driven pPUR-KE vector (pPUR/tRNARz3 and pPUR/tRNARz4); the ribozyme vectors were co-transfected with the target vector (pCAG/Sry). A suppressive action (up to approx. 60%) was confirmed for pCAG/HHRz and pPUR/tRNARz3 upon the transiently expressed exogenously introduced Sry in M15 cultured cells.

Human Y-chromosome variation and male dysfunction

The Y-chromosome is responsible for sex determination in mammals, which is triggered by the expression of the SRY gene, a testis-determining factor. This particular gene, as well as other genes related to male fertility, are located in the non-recombining portion of the Y (NRY), a specific region that encompasses 95% of the human Y-chromosome. The other 5% is composed of the pseudo-autosomal regions (PARs) at the tips of Yp and Yq, a X-chromosome homologous region used during male meiosis for the correct pairing of sexual chromosomes. Despite of the large size of the human NRY (about 60 Mb), only a few active genes are found in this region, most of which are related to fertility. Recently, several male fertility dysfunctions were associated to microdeletions by STS mapping. Now that the complete genetic map of the human Y-chromosome is available, the role of particular NRY genes in fertility dysfunctions is being investigated. Besides, along with the description of several nucleotide and structural variations in the Y-chromosome, the association between phenotype and genotype is being addressed more precisely. Particularly, several research groups are investigating the association between Y-chromosome types and susceptibility to certain male dysfunctions in different population backgrounds. New insights on the role of the Y-chromosome and maleness are being envisaged by this approach.

NHERF2/SIP-1 interacts with mouse SRY via a different mechanism than human SRY

In mammals, male sex determination is controlled by the SRY protein, which drives differentiation of the bipotential embryonic gonads into testes by activating the Sertoli cell differentiation program. The morphological effects of SRY are well documented; however, its molecular mechanism of action remains unknown. Moreover, SRY proteins display high sequence variability among mammalian species, which makes protein motifs difficult to delineate. We previously isolated SIP-1/NHERF2 as a human SRY-interacting protein. SIP-1/NHERF2, a PDZ protein, interacts with the C-terminal extremity of the human SRY protein. Here we showed that the interaction of SIP-1/NHERF2 and SRY via the SIP-1/NHERF2 PDZ1 domain is conserved in mice. However, the interaction occurs via a domain that is internal to the mouse SRY protein and involves a different recognition mechanism than human SRY. Furthermore, we show that mouse and human SRY induce nuclear accumulation of the SIP-1/NHERF2 protein in cultured cells. Finally, a transgenic mouse line expressing green fluorescent protein under the control of the mouse Sry promoter allowed us to show that SRY and SIP-1/NHERF2 are co-expressed in the nucleus of pre-Sertoli cells during testis determination. Taken together, our results suggested that the function of SIP-1/NHERF2 as an SRY cofactor during testis determination is conserved between human and mouse.

Defective Calmodulin-Mediated Nuclear Transport of the Sex-Determining Region of the Y Chromosome (SRY) in XY Sex Reversal

The sex-determining region of the Y chromosome (SRY) plays a key role in human sex determination, as mutations in SRY can cause XY sex reversal. Although some SRY missense mutations affect DNA binding and bending activities, it is unclear how others contribute to disease. The high mobility group domain of SRY has two nuclear localization signals (NLS). Sex-reversing mutations in the NLSs affect nuclear import in some patients, associated with defective importin-β binding to the C-terminal NLS (c-NLS), whereas in others, importin-β recognition is normal, suggesting the existence of an importin-β-independent nuclear import pathway. The SRY N-terminal NLS (n-NLS) binds calmodulin (CaM) in vitro, and here we show that this protein interaction is reduced in vivo by calmidazolium, a CaM antagonist. In calmidazolium-treated cells, the dramatic reduction in nuclear entry of SRY and an SRY-c-NLS mutant was not observed for two SRY-n-NLS mutants. Fluorescence spectroscopy studies reveal an unusual conformation of SRY.CaM complexes formed by the two n-NLS mutants. Thus, CaM may be involved directly in SRY nuclear import during gonadal development, and disruption of SRY.CaM recognition could underlie XY sex reversal. Given that the CaM-binding region of SRY is well-conserved among high mobility group box proteins, CaM-dependent nuclear import may underlie additional disease states.

New insights into the regulation of mammalian sex determination and male sex differentiation

In mammals, sex development is a genetically and hormonally controlled process that begins with the establishment of chromosomal or genetic sex (XY or XX) at conception. At approximately 6 to 7 weeks of human gestation or embryonic day e11.5 in the mouse, expression of the Y chromosome-linked sex determining gene called SRY (described in detail in this chapter) then initiates gonadal differentiation, which is the formation of either a testis (male) or an ovary (female). Male sex differentiation (development of internal and external reproductive organs and acquisition of male secondary sex characteristics) is then controlled by three principal hormones produced by the testis: Mullerian inhibiting substance (MIS) or anti-Mullerian hormone (AMH), testosterone, and insulin-like factor 3 (INSL3). In the absence of these critical testicular hormones, female sex differentiation ensues. This sequential, three-step process of mammalian sex development is also known as the Jost paradigm. With the advent of modern biotechnologies over the past decade, such as transgenics, array-based gene profiling, and proteomics, the field of mammalian sex determination has witnessed a remarkable boost in the understanding of the genetics and complex molecular mechanisms that regulate this fundamental biological event. Consequently, a number of excellent reviews have been devoted to this topic. The purpose of the present chapter is to provide an overview of selected aspects of mammalian sex determination and differentiation with an emphasis on studies that have marked this field of study.

Cloning and expression analysis of gonadogenesis-associated gene SPATA4 from rainbow trout (Oncorhynchus mykiss)

Gonadogenesis is a complicated process which involves multi-gene interactions. A rainbow trout (Oncorhynchus mykiss) gene spermatogenesis associated 4 (SPATA4) was cloned and characterized from adult rainbow trout testis. The cDNA sequence of rainbow trout SPATA4 contains an open reading frame of 1, 081 nucleatides encoding a putative protein of 259 amino acids. The putative protein from rainbow trout shares a 76.8% homology with zebrafish SPATA4. No trans-membrane regions or signal peptide were detected using bioinformatics methods. Subcellular localization analysis revealed that rainbow trout SPATA4 was a nuclear protein with highest possibility (39.1%). Multi-tissue reverse transcriptase PCR (RT-PCR) was performed to examine the distribution of rainbow trout SPATA4 in eleven organs of adult rainbow trout. The result demonstrated that this gene express specifically in testis and slight amount of expression was detected in ovary. Further analysis of SPATA4 characterization and function in rainbow trout may provide insight into the understanding of gonadogenesis process.

Epigenetics and the germline

Epigenetic processes affect three stages of germline development, namely (1) specification and formation of primordial germ cells and their germline derivatives through lineage-specific epigenetic modifications, in the same manner as other embryonic lineages are formed, (2) a largely genome-wide erasure and re-establishment of germline-specific epigenetic modifications that only occurs in the embryonic primordial germ cell lineage, followed by re-establishment of sex-specific patterns during gametogenesis, and (3) differential epigenetic modifications to the mature male and female gamete genomes shortly after fertilisation. This review will detail current knowledge of these three processes both at the genome-wide level and at specific imprinted loci. The consequences of epigenetic perturbation are discussed and new in vitro models which may allow further understanding of a difficult developmental period to study, especially in the human, are highlighted.

Two types of aromatase with different encoding genes, tissue distribution and developmental expression in Nile tilapia (Oreochromis niloticus)

We isolated a novel type of aromatase cDNA from a Nile tilapia (Oreochromis niloticus) ovary cDNA library. Because this aromatase is phylogenetically related to brain aromatase (CYP19b) of goldfish, zebrafish and sea bass, we named it tilapia CYP19b (tCYP19b). tCYP19b encodes a protein that is predicted to consist of 495 residues and have 63.8% homology with the aromatase (tCYP19a) we previously isolated from the same source. In vitro transient transfection of cultured COS7 cells demonstrated that tCYP19b codes a functional protein to catalyze estrogen production from an androgen substrate. RT-PCR and Northern hybridization analysis showed that tCYP19b was expressed at a high level in the brain and at a low level in a wide variety of other tissues, whereas tCYP19a was mainly present in the ovary and its level significantly increased during the vitellogenic stage. RT-PCR also detected tCYP19b expression in brain and gonad tissues of both female and male tilapia during sex differentiation, but tCYP19a was only found in the ovary of the fry at that period. These results suggest that tCYP19a plays a key role in sex differentiation and ovarian development. We also isolated genes of two tilapia aromatases. Based on the location of the transcription initiation site, we predicted that there is one promoter for tCYP19a and three promoters for tCYP19b. Although the two aromatase isoforms have similar gene structures in the coding region, we found that the binding regions of SF-1/Ad4 BP region, WT1-KTS and SRY, which are sex-determining factors in mammals, are present in the 5' flank region of tCYP19a but not tCYP19b. A similar situation is present in promoters of zebrafish and goldfish aromatase isoforms. This data indicates that CYP19a plays a decisive role in sex differentiation of those species. The unique presence of the ERE motif in the tCYP19b promoter and the high expression of tCYP19b in the brain support that CYP19b is mainly involved in estrogen-mediated neural estrogen synthesis.

Fine mapping of chromosome 17 translocation breakpoints > or = 900 Kb upstream of SOX9 in acampomelic campomelic dysplasia and a mild, familial skeletal dysplasia

Previously, our group reported a five-generation family in which a balanced t(13;17) translocation is associated with a spectrum of skeletal abnormalities, including Robin sequence, hypoplastic scapulae, and a missing pair of ribs. Using polymerase chain reaction (PCR) with chromosome-specific markers to analyze DBA from somatic cell hybrids containing the derivative translocation chromosomes, we narrowed the breakpoint on each chromosome. Subsequent sequencing of PCR products spanning the breakpoints identified the breaks precisely. The chromosome 17 breakpoint maps approximately 932 kb upstream of the sex-determining region Y (SRY)-related high-mobility group box gene (SOX) within a noncoding transcript represented by two IMAGE cDNA clones. A growing number of reports have implicated chromosome 17 breakpoints at a distance of up to 1 Mb from SOX9 in some cases of campomelic dysplasia (CD). Although this multigeneration family has a disorder that shares some features with CD, their phenotype is significantly milder than any reported cases of (nonmosaic) CD. Therefore, this case may represent an etiologically distinct skeletal dysplasia or may be an extremely mild familial example of CD, caused by the most proximal translocation breakpoint from SOX9 reported to date. In addition, we have refined the breakpoint in a acampomelic CD case described elsewhere and have found that it lies approximately 900 kb upstream of SOX9.

Embryonic reversions and lineage infidelities in tumour cells: genome-based models and role of genetic instability

Reversions to "embryonic precursor"-type cells and infidelities of tumour cell lineage (including metaplasias) have been recognized as aspects of various tumour types since the 19th century. Since then, evidence of these phenomena has been obtained from numerous clinical, biochemical, immunological and molecular biological studies. In particular, microarray studies have suggested that "aberrant" expressions of relevant genes are common. An unexplained aspect of the results of these studies is that, in many tumour types, the embryonic reversion or lineage infidelity only occurs in a proportion of cases. As a parallel development during the molecular biological investigation of tumours over the last several decades, genetic instability has been found much more marked, at least in some preparations of tumour cells, than that identified by means of previous karyotypic investigations of tumours. This study reviews examples of embryonic reversion and lineage infidelity phenomena, which have derived from the various lines of investigation of cancer over the last 150 or so years. Four categories of circumstances of the occurrence of embryonic reversions or lineage infidelities have been identified - (i) as part of the defining phenotype of the tumour, and hence being presumably integral to the tumour type, (ii) present ab initio in only some cases of the tumour type, and presumably being regularly associated with, but incidental to, the essential features of the tumour type, (iii) occurring later in the course of the disease and thus being possibly a manifestation of in vivo genetic instability and "tumour progression" and (iv) arising probably by genetic instability, during the processes, especially cell culture, associated with ex vivo investigations. Genomic models are described which might account for the origin of these phenomena in each of these circumstances.

The endless quest for sex determination genes

Disorders in human sex determination cause defects in gonadal function and can result in a spectrum of abnormalities in the internal and external genitalia, ranging from relatively mild sexual ambiguities to complete sex reversal. Several genes involved in sex determination have been validated in humans, and activities of their gene products are being elucidated, particularly in mouse models. However, how these genes interact in an overall process remains far from clear, and it is probable that many additional genes are involved. Management of patients with pathologies in sex determination and subsequent differentiation is currently under debate, but will require not only an understanding of the multiple definitions of an individual's sex but also an increased knowledge of the molecular mechanisms involved in sex determination.