Loss of function mutation in the palmitoyl-transferase HHAT leads to syndromic 46,XY disorder of sex development by impeding Hedgehog protein palmitoylation and signaling

Diverse genetic causes of amenorrhea in an ethnically homogeneous cohort and an evolving approach to diagnosis

RESEARCH QUESTION

Premature ovarian insufficiency (POI) is characterised by amenorrhea associated with elevated follicle stimulating hormone (FSH) under the age of 40 years and affects 1-3.7% women. Genetic factors explain 20-30% of POI cases, but most causes remain unknown despite genomic advancements.

DESIGN

We used whole exome sequencing (WES) in four Iranian families, validated variants via Sanger sequencing, and conducted the Acyl-cLIP assay to measure HHAT enzyme activity.

RESULTS

Despite ethnic homogeneity, WES revealed diverse genetic causes, including a novel homozygous nonsense variant in SYCP2L, impacting synaptonemal complex (SC) assembly, in the first family. Interestingly, the second family had two independent causes for amenorrhea - the mother had POI due to a novel homozygous loss-of-function variant in FANCM (required for chromosomal stability) and her daughter had primary amenorrhea due to a novel homozygous GNRHR (required for gonadotropic signalling) frameshift variant. WES analysis also provided cytogenetic insights. WES revealed one individual was in fact 46, XY and had a novel homozygous missense variant of uncertain significance in HHAT, potentially responsible for complete sex reversal although functional assays did not support impaired HHAT activity. In the remaining individual, WES indicated likely mosaic Turners with the majority of X chromosome variants having an allelic balance of ∼85% or ∼15%. Microarray validated the individual had 90% 45,XO.

CONCLUSIONS

This study demonstrates the diverse causes of amenorrhea in a small, isolated ethnic cohort highlighting how a genetic cause in one individual may not clarify familial cases. We propose that, in time, genomic sequencing may become a single universal test required for the diagnosis of infertility conditions such as POI.

A Homozygous Missense Variant in Hedgehog Acyltransferase (HHAT) Gene Associated with 46,XY Gonadal Dysgenesis

INTRODUCTION

Disorders of gonadal development represent a clinically and genetically heterogeneous group of DSD, and the etiology in many cases remains unknown, indicating that our knowledge of factors controlling sex determination is still limited.

METHODS

We describe a 46,XY DSD patient from Egypt. The patient was reared as female, born to consanguineous parents, and was referred to us at the age of 5 years because of ambiguous genitalia. On examination, the girl was microcephalic (head circumference -3 SD), but her height and weight were normal for her age and sex.

RESULTS

Exome sequencing identified a homozygous variant in the hedgehog acyltransferase (HHAT) gene, which encodes an enzyme that is required for multimerization and signaling potency of the hedgehog secreted proteins. The variant is a novel homozygous missense change c.1329C>A (p.N443K), located within transmembrane domain 9, which segregated with the phenotype in the family.

DISCUSSION/CONCLUSION

Our results expand the phenotypic spectrum associated with HHAT variants to include 46,XY gonadal dysgenesis and reinforce the role of exome sequencing in unraveling new genes that play a pivotal role in sexual development.

Hedgehog signaling regulates Wolffian duct development through the primary cilium†

Primary cilia play pivotal roles in embryonic patterning and organogenesis through transduction of the Hedgehog signaling pathway (Hh). Although mutations in Hh morphogens impair the development of the gonads and trigger male infertility, the contribution of Hh and primary cilia in the development of male reproductive ductules, including the epididymis, remains unknown. From a Pax2Cre; IFT88fl/fl knock-out mouse model, we found that primary cilia deletion is associated with imbalanced Hh signaling and morphometric changes in the Wolffian duct (WD), the embryonic precursor of the epididymis. Similar effects were observed following pharmacological blockade of primary cilia formation and Hh modulation on WD organotypic cultures. The expression of genes involved in extracellular matrix, mesenchymal-epithelial transition, canonical Hh and WD development was significantly altered after treatments. Altogether, we identified the primary cilia-dependent Hh signaling as a master regulator of genes involved in WD development. This provides new insights regarding the etiology of sexual differentiation and male infertility issues.

Additional evidence for the role of chromosomal imbalances and SOX8, ZNRF3 and HHAT gene variants in early human testis development

BACKGROUND

Forty-six ,XY Differences/Disorders of Sex Development (DSD) are characterized by a broad phenotypic spectrum ranging from typical female to male with undervirilized external genitalia, or more rarely testicular regression with a typical male phenotype. Despite progress in the genetic diagnosis of DSD, most 46,XY DSD cases remain idiopathic.

METHODS

To determine the genetic causes of 46,XY DSD, we studied 165 patients of Tunisian ancestry, who presented a wide range of DSD phenotypes. Karyotyping, candidate gene sequencing, and whole-exome sequencing (WES) were performed.

RESULTS

Cytogenetic abnormalities, including a high frequency of sex chromosomal anomalies (85.4%), explained the phenotype in 30.9% (51/165) of the cohort. Sanger sequencing of candidate genes identified a novel pathogenic variant in the SRY gene in a patient with 46,XY gonadal dysgenesis. An exome screen of a sub-group of 44 patients with 46,XY DSD revealed pathogenic or likely pathogenic variants in 38.6% (17/44) of patients.

CONCLUSION

Rare or novel pathogenic variants were identified in the AR, SRD5A2, ZNRF3, SOX8, SOX9 and HHAT genes. Overall our data indicate a genetic diagnosis rate of 41.2% (68/165) in the group of 46,XY DSD.

Muscle spasms as presenting feature of Nivelon-Nivelon-Mabile syndrome

Hedgehog acyltransferase gene (HHAT)-associated Nivelon-Nivelon-Mabile syndrome (NNMS) is a rare genetic disorder of multiple system involvement with microcephaly, central nervous system malformations, skeletal dysplasia, and 46,XY sex reversal. Other variable and inconsistent features reported in this disorder are muscle spasms, facial dysmorphism, prenatal onset growth restriction, microphthalmia, and holoprosencephaly. This is the sixth postnatal reported patient with biallelic variants in HHAT gene, who presented with microcephaly, short stature, muscle hypertrophy, muscle spasms, and facial dysmorphism. The most prominent and presenting finding in this patient were muscle hypertrophy and muscle spasms which had a clinical response to phenytoin and acetazolamide treatment. Our report emphasizes the phenotypic variability of NNMS and further reiterates muscle spasms as an important clinical manifestation of this extremely rare condition.

Novel compound heterozygous mutations in the desert hedgehog (DHH) gene in cases of siblings with 46,XY disorders of sexual development

Background

Disorders of sex development (DSD) are congenital disorders in which the development of the chromosomal, gonadal, or anatomical sex is atypical. Mutations in various genes can impede gonadal development, hormone synthesis, or hormone function and cause DSD.

Methods

Exome sequencing was performed for two siblings with 46,XY DSD. All mutations identified by exome sequencing were confirmed by Sanger sequencing.

Results

The 13-month-old younger sibling had a female appearance of the external genital with a clitoris that was assessed as Prader III and scored 2 in the external masculinization score evaluative test. The 16-year-old elder sibling had severe hypospadias. Exome sequencing revealed compound heterozygous mutations in exon 3 of DHH in the siblings with 46,XY DSD. The frameshift mutation (NM_021044.3: c.602delC) was derived from the father and was predicted to be deleterious. The (c.937G > T) substitution mutation was derived from the mother.

Conclusions

Novel compound heterozygous mutations of DHH led to 46,XY DSD in two siblings. This study expands the phenotypic mutation spectra of DHH in patients with 46,XY DSD.

The Use of Genetics for Reaching a Diagnosis in XY DSD

Reaching a firm diagnosis is vital for the long-term management of a patient with a difference or disorder of sex development (DSD). This is especially the case in XY DSD where the diagnostic yield is particularly low. Molecular genetic technology is playing an increasingly important role in the diagnostic process, and it is highly likely that it will be used more often at an earlier stage in the diagnostic process. In many cases of DSD, the clinical utility of molecular genetics is unequivocally clear, but in many other cases there is a need for careful exploration of the benefit of genetic diagnosis through long-term monitoring of these cases. Furthermore, the incorporation of molecular genetics into the diagnostic process requires a careful appreciation of the strengths and weaknesses of the evolving technology, and the interpretation of the results requires a clear understanding of the wide range of conditions that are associated with DSD.

Loss of NEDD4 causes complete XY gonadal sex reversal in mice

Gonadogenesis is the process wherein two morphologically distinct organs, the testis and the ovary, arise from a common precursor. In mammals, maleness is driven by the expression of Sry. SRY subsequently upregulates the related family member Sox9 which is responsible for initiating testis differentiation while repressing factors critical to ovarian development such as FOXL2 and β-catenin. Here, we report a hitherto uncharacterised role for the ubiquitin-protein ligase NEDD4 in this process. XY Nedd4-deficient mice exhibit complete male-to-female gonadal sex reversal shown by the ectopic upregulation of Foxl2 expression at the time of gonadal sex determination as well as insufficient upregulation of Sox9. This sex reversal extends to germ cells with ectopic expression of SYCP3 in XY Nedd4-/- germ cells and significantly higher Sycp3 transcripts in XY and XX Nedd4-deficient mice when compared to both XY and XX controls. Further, Nedd4-/- mice exhibit reduced gonadal precursor cell formation and gonadal size as a result of reduced proliferation within the developing gonad as well as reduced Nr5a1 expression. Together, these results establish an essential role for NEDD4 in XY gonadal sex determination and development and suggest a potential role for NEDD4 in orchestrating these cell fate decisions through the suppression of the female pathway to ensure proper testis differentiation.

Novel variant in HHAT as a cause of different sex development with partial gonadal dysgenesis associated with microcephaly, eye defects, and distal phalangeal hypoplasia of both thumbs: Case report

The palmitoylation of the Hedgehog (Hh) family of morphogens, named sonic hedgehog (SHH), desert hedgehog (DHH), and Indian hedgehog (IHH), is crucial for effective short- and long-range signaling. The hedgehog acyltransferase (HHAT) attaches the palmitate molecule to the Hh; therefore, variants in HHAT cause a broad spectrum of phenotypes. A missense HHAT novel variant c.1001T>A/p.(Met334Lys) was described in a patient first referred for a 46,XY different sexual development with partial gonadal dysgenesis but with microcephaly, eye defects, and distal phalangeal hypoplasia of both thumbs. The in silico analysis of the variant predicted an affectation of the nearest splicing site. Thus, in vitro minigene studies were carried out, which demonstrated that the variant does not affect the splicing. Subsequent protein in silico studies supported the pathogenicity of the variant, and, in conclusion, this was considered the cause of the patient's phenotype.

Genetics of 46,XY gonadal dysgenesis

In 46,XY men, testis is determined by a genetic network(s) that both promotes testis formation and represses ovarian development. Disruption of this process results in a lack of testis-determination and affected individuals present with 46,XY gonadal dysgenesis (GD), a part of the spectrum of Disorders/Differences of Sex Development/Determination (DSD). A minority of all cases of GD are associated with pathogenic variants in key players of testis-determination, SRY, SOX9, MAP3K1 and NR5A1. However, most of the cases remain unexplained. Recently, unbiased exome sequencing approaches have revealed new genes and loci that may cause 46,XY GD. We critically evaluate the evidence to support causality of these factors and describe how functional studies are continuing to improve our understanding of genotype-phenotype relationships in genes that are established causes of GD. As genomic data continues to be generated from DSD cohorts, we propose several recommendations to help interpret the data and establish causality.

Structure, mechanism, and inhibition of Hedgehog acyltransferase

The Sonic Hedgehog (SHH) morphogen pathway is fundamental for embryonic development and stem cell maintenance and is implicated in various cancers. A key step in signaling is transfer of a palmitate group to the SHH N terminus, catalyzed by the multi-pass transmembrane enzyme Hedgehog acyltransferase (HHAT). We present the high-resolution cryo-EM structure of HHAT bound to substrate analog palmityl-coenzyme A and a SHH-mimetic megabody, revealing a heme group bound to HHAT that is essential for HHAT function. A structure of HHAT bound to potent small-molecule inhibitor IMP-1575 revealed conformational changes in the active site that occlude substrate binding. Our multidisciplinary analysis provides a detailed view of the mechanism by which HHAT adapts the membrane environment to transfer an acyl chain across the endoplasmic reticulum membrane. This structure of a membrane-bound O-acyltransferase (MBOAT) superfamily member provides a blueprint for other protein-substrate MBOATs and a template for future drug discovery.

The Desert Hedgehog Signalling Pathway in Human Gonadal Development and Differences of Sex Development

While the Hedgehog signalling pathway is implicated in numerous developmental processes and maladies, variants in the Desert Hedgehog (DHH) ligand underlie a condition characterised by 46,XY gonadal dysgenesis with or without peripheral neuropathy. We discuss here the role and regulation of DHH and its signalling pathway in the developing gonads and examine the current understanding of how disruption to this pathway causes this difference of sex development (DSD) in humans.

Cholesterol Contributes to Male Sex Differentiation Through Its Developmental Role in Androgen Synthesis and Hedgehog Signaling

Two specialized functions of cholesterol during fetal development include serving as a precursor to androgen synthesis and supporting hedgehog (HH) signaling activity. Androgens are produced by the testes to facilitate masculinization of the fetus. Recent evidence shows that intricate interactions between the HH and androgen signaling pathways are required for optimal male sex differentiation and defects of either can cause birth anomalies indicative of 46,XY male variations of sex development (VSD). Further, perturbations in cholesterol synthesis can cause developmental defects, including VSD, that phenocopy those caused by disrupted androgen or HH signaling, highlighting the functional role of cholesterol in promoting male sex differentiation. In this review, we focus on the role of cholesterol in systemic androgen and local HH signaling events during fetal masculinization and their collective contributions to pediatric VSD.

Hedgehog acyl-transferase-related multiple congenital anomalies: Report of an additional family and delineation of the syndrome

This study includes previous reports of four affected individuals from two unrelated families with hedgehog acyl-transferase (HHAT)-related multiple congenital anomaly syndrome. Microcephaly, small cerebellar vermis, holoprosencephaly, agenesis of corpus callosum, intellectual disability, short stature, skeletal dysplasia, microphthalmia-anophthalmia, and sex reversal constitute the phenotypic spectrum of this condition with variable expression. We report an additional family with three affected conceptuses: two abortuses and one living proband. We did proband-parents trio exome sequencing and identified a biallelic in-frame deletion c.365_367del; (p.Thr122del) in exon 5 of HHAT. With this report, we delineate the phenotype and allelic heterogeneity of the HHAT-related multiple congenital anomaly syndrome.

Advances in genomic diagnosis of a large cohort of Egyptian patients with disorders of sex development

Disorders/differences of sex development (DSD) comprise a group of congenital disorders that affect the genitourinary tract and usually involve the endocrine and reproductive system. The aim of this work was to identify genetic variants responsible for disorders of human urogenital development in a cohort of Egyptian patients. This three-year study included 225 patients with various DSD forms, referred to the genetic DSD and endocrinology clinic, National Research Centre, Egypt. The patients underwent thorough clinical examination, hormonal and imaging studies, detailed cytogenetic and fluorescence in situ hybridization analysis, and molecular sequencing of genes known to commonly cause DSD including AR, SRD5A2, 17BHSD3, NR5A1, SRY, and WT1. Whole exome sequencing (WES) was carried out for 18 selected patients. The study revealed a high rate of sex chromosomal DSD (33%) with a wide array of cytogenetic abnormalities. Sanger sequencing identified pathogenic variants in 33.7% of 46,XY patients, while the detection rate of WES reached 66.7%. Our patients showed a different mutational profile compared with that reported in other populations with a predominance of heritable DSD causes. WES identified rare and novel pathogenic variants in NR5A1, WT1, HHAT, CYP19A1, AMH, AMHR2, and FANCA and in the X-linked genes ARX and KDM6A. In addition, digenic inheritance was observed in two of our patients and was suggested to be a cause of the phenotypic variability observed in DSD.

Palmitoylation of Hedgehog proteins by Hedgehog acyltransferase: roles in signalling and disease

Hedgehog acyltransferase (Hhat), a member of the membrane-bound O-acyltransferase (MBOAT) family, catalyses the covalent attachment of palmitate to the N-terminus of Hedgehog proteins. Palmitoylation is a post-translational modification essential for Hedgehog signalling. This review explores the mechanisms involved in Hhat acyltransferase enzymatic activity, similarities and differences between Hhat and other MBOAT enzymes, and the role of palmitoylation in Hedgehog signalling. In vitro and cell-based assays for Hhat activity have been developed, and residues within Hhat and Hedgehog essential for palmitoylation have been identified. In cells, Hhat promotes the transfer of palmitoyl-CoA from the cytoplasmic to the luminal side of the endoplasmic reticulum membrane, where Shh palmitoylation occurs. Palmitoylation is required for efficient delivery of secreted Hedgehog to its receptor Patched1, as well as for the deactivation of Patched1, which initiates the downstream Hedgehog signalling pathway. While Hhat loss is lethal during embryogenesis, mutations in Hhat have been linked to disease states or abnormalities in mice and humans. In adults, aberrant re-expression of Hedgehog ligands promotes tumorigenesis in an Hhat-dependent manner in a variety of different cancers, including pancreatic, breast and lung. Targeting hedgehog palmitoylation by inhibition of Hhat is thus a promising, potential intervention in human disease.

The FKBP4 Gene, Encoding a Regulator of the Androgen Receptor Signaling Pathway, Is a Novel Candidate Gene for Androgen Insensitivity Syndrome

Androgen insensitivity syndrome (AIS), manifesting incomplete virilization in 46,XY individuals, is caused mostly by androgen receptor (AR) gene mutations. Therefore, a search for AR mutations is a routine approach in AIS diagnosis. However, some AIS patients lack AR mutations, which complicates the diagnosis. Here, we describe a patient suffering from partial androgen insensitivity syndrome (PAIS) and lacking AR mutations. The whole exome sequencing of the patient and his family members identified a heterozygous FKBP4 gene mutation, c.956T>C (p.Leu319Pro), inherited from the mother. The gene encodes FKBP prolyl isomerase 4, a positive regulator of the AR signaling pathway. This is the first report describing a FKBP4 gene mutation in association with a human disorder of sexual development (DSD). Importantly, the dysfunction of a homologous gene was previously reported in mice, resulting in a phenotype corresponding to PAIS. Moreover, the Leu319Pro amino acid substitution occurred in a highly conserved position of the FKBP4 region, responsible for interaction with other proteins that are crucial for the AR functional heterocomplex formation and therefore the substitution is predicted to cause the disease. We proposed the FKBP4 gene as a candidate AIS gene and suggest screening that gene for the molecular diagnosis of AIS patients lacking AR gene mutations.

DHH pathogenic variants involved in 46,XY disorders of sex development differentially impact protein self-cleavage and structural conformation

In humans, pathogenic variants in the DHH gene underlie cases of 46,XY gonadal dysgenesis. DHH is part of the Hedgehog family of proteins, which require extensive processing, including self-cleavage of the precursor for efficient signalling. In our work, we have assessed the effect of several human DHH pathogenic variants involved in recessive complete or partial gonadal dysgenesis, on protein processing and sub-cellular localization. We found that a subset of variants was unable to perform self-cleavage, which correlated albeit not perfectly with an altered subcellular localization of the resulting proteins. For the processing-proficient variants, we used structural modelling tools and molecular dynamic (MD) simulations to predict the potential impact of the variants on protein conformation and/or interaction with partners. Our study contributes to a better understanding of the molecular mechanisms involved in DHH dysfunction leading to 46,XY disorders of sex development.

The gene encoding the ketogenic enzyme HMGCS2 displays a unique expression during gonad development in mice

Disorders/differences of sex development (DSD) cause profound psychological and reproductive consequences for the affected individuals, however, most are still unexplained at the molecular level. Here, we present a novel gene, 3-hydroxy-3-methylglutaryl coenzyme A synthase 2 (HMGCS2), encoding a metabolic enzyme in the liver important for energy production from fatty acids, that shows an unusual expression pattern in developing fetal mouse gonads. Shortly after gonadal sex determination it is up-regulated in the developing testes following a very similar spatial and temporal pattern as the male-determining gene Sry in Sertoli cells before switching to ovarian enriched expression. To test if Hmgcs2 is important for gonad development in mammals, we pursued two lines of investigations. Firstly, we generated Hmgcs2-null mice using CRISPR/Cas9 and found that these mice had gonads that developed normally even on a sensitized background. Secondly, we screened 46,XY DSD patients with gonadal dysgenesis and identified two unrelated patients with a deletion and a deleterious missense variant in HMGCS2 respectively. However, both variants were heterozygous, suggesting that HMGCS2 might not be the causative gene. Analysis of a larger number of patients in the future might shed more light into the possible association of HMGCS2 with human gonadal development.

Male Hypogonadism and Disorders of Sex Development

Disorders of Sex Development (DSD) are congenital anomalies in which there is a discordance between chromosomal, genetic, gonadal, and/or internal/external genital sex. In XY individuals, the process of fetal sex differentiation can be disrupted at the stage of gonadal differentiation, resulting in gonadal dysgenesis, a form of early fetal-onset primary hypogonadism characterized by insufficient androgen and anti-Müllerian hormone (AMH) production, which leads to the development of ambiguous or female genitalia. The process of sex differentiation can also be disrupted at the stage of genital differentiation, due to isolated defects in androgen or AMH secretion, but not both. These are forms of fetal-onset hypogonadism with dissociated gonadal dysfunction. In this review, we present a perspective on impaired testicular endocrine function, i.e., fetal-onset male hypogonadism, resulting in incomplete virilization at birth.

Phthalate-Induced Fetal Leydig Cell Dysfunction Mediates Male Reproductive Tract Anomalies

Male fetal Leydig cells in the testis secrete androgen and insulin-like 3, determining the sexual differentiation. The abnormal development of fetal Leydig cells could lead to the reduction of androgen and insulin-like 3, thus causing the male reproductive tract anomalies in male neonates, including cryptorchidism and hypospadias. Environmental pollutants, such as phthalic acid esters (phthalates), can perturb the development and differentiated function of Leydig cells, thereby contributing to the reproductive toxicity in the male. Here, we review the epidemiological studies in humans and experimental investigations in rodents of various phthalates. Most of phthalates disturb the expression of various genes encoded for steroidogenesis-related proteins and insulin-like 3 in fetal Leydig cells and the dose-additive effects are exerted after exposure in a mixture.

Paraquat exposure delays stem/progenitor Leydig cell regeneration in the adult rat testis

Paraquat, a widely used nonselective herbicide, is a serious hazard to human health. However, the effects of paraquat on the male reproductive system remain unclear. In this study, adult male Sprague Dawley rats were intraperitoneally injected ethane dimethane sulfonate (EDS, 75 mg/kg) to initiate a regeneration of Leydig cells. EDS-treated rats were orally exposed to paraquat (0.5, 2, 8 mg/kg/day) from post-EDS day 17 to day 28 and effects of paraquat on Leydig and Sertoli cell functions on post-EDS day 35 and day 56 were investigated. Paraquat significantly decreased serum testosterone levels at 2 and 8 mg/kg. Paraquat lowered Leydig cell Hsd17b3, Srd5a1, and Hsd11b1 mRNA levels but increased Hsd3b1 on post-EDS day 35. Paraquat lowered Cyp11a1, Cyp17a1, and Hsd11b1 but increased Srd5a1 on post-EDS day 56. However, paraquat did not alter Leydig cell number and PCNA labeling index. Epididymal staining showed that few sperms were observed in paraquat-treated rats. Primary culture of adult Leydig cells showed that paraquat diminished testosterone output and induced reactive oxygen species generation at 1 and 10 μM and apoptosis rate at 10 μM. In conclusion, a short-term exposure to paraquat delays Leydig cell regeneration from stem/progenitor Leydig cells, causing low production of testosterone and an arrest of spermatogenesis.

Prioritization and comprehensive analysis of genes associated with melanoma

Melanoma is a malignant tumor derived from melanocytes, which occurs mostly in the skin. A major challenge in cancer research is the biological interpretation of the complexity of cancer somatic mutation profiles. The aim of the present study was to obtain a comprehensive understanding of the formation and development of melanoma and to identify its associated genes. In the present study, a pipeline was proposed for investigating key genes associated with melanoma based on the Online Mendelian Inheritance in Man and Search Tool for the Retrieval of Interacting Genes/Proteins databases through a random walk model. Additionally, functional enrichment analysis was performed for key genes associated with melanoma. This identified a total of 17 biological processes and 30 pathways which may be associated with melanoma. In addition, melanoma-specific network analysis followed by Kaplan-Meier analysis along with log-rank tests identified tyrosinase, hedgehog acyltransferase, BRCA1-associated protein 1 and melanocyte inducing transcription factor as potential therapeutic targets for melanoma. In conclusion, the present study increased the knowledge of melanoma progression and may be helpful for improving its prognosis.

Saccharomyces cerevisiae mitochondrial Por1/yVDAC1 (voltage-dependent anion channel 1) interacts physically with the MBOAT O-acyltransferase Gup1/HHATL in the control of cell wall integrity and programmed cell death

Gup1 is the yeast counterpart of the high eukaryotes HHATL. This and the close homologue Gup2/HHAT regulate the Hedgehog morphogenic, developmental pathway. In yeasts, a similar paracrine pathway is not known though the Δgup1 mutant is associated with morphology and proliferation/death processes. As a first step toward identifying the actual molecular/enzymatic function of Gup1, this work identified by co-immunoprecipitation the yeast mitochondria membrane VDAC1/Por1 as a physical partner of Gup1. Gup1 locates in the ER and the plasma membrane. It was now confirmed to further locate, as Por1, in the mitochondrial sub-cellular fraction. The yeast Por1-Gup1 association was found important for (i) the sensitivity to cell wall perturbing agents and high temperature, (ii) the differentiation into structured colonies, (iii) the size achieved by multicellular aggregates/mats and (iv) acetic-acid-induced Programmed Cell Death. Moreover, the absence of Gup1 increased the levels of POR1 mRNA, while decreasing the amounts of intracellular Por1, which was concomitantly previously known to be secreted by the mutant but not by wt. Additionally, Por1 patchy distribution in the mitochondrial membrane was evened. Results suggest that Por1 and Gup1 collaborate in the control of colony morphology and mat development, but more importantly of cellular integrity and death.

Biallelic novel missense HHAT variant causes syndromic microcephaly and cerebellar-vermis hypoplasia

We report two siblings with microcephaly, early infantile onset seizures, and cerebellar vermis hypoplasia, in whom whole exome sequencing revealed a novel homozygous missense (c.770T>C, p.[Leu257Pro]) variant in the hedgehog acyl-transferase gene (HHAT), encoding an enzyme required for the attachment of palmitoyl residues that are critical for multimerization and long and short range hedgehog signaling. There is a report of one family with Nivelon-Nivelon-Mabille syndrome in which HHAT was proposed as the likely candidate gene. The phenotypic overlap with the family we report herein provides further evidence implicating HHAT in cerebellar development and the pathogenesis of this rare spectrum.

Translating genomics to the clinical diagnosis of disorders/differences of sex development

The medical and psychosocial challenges faced by patients living with Disorders/Differences of Sex Development (DSD) and their families can be alleviated by a rapid and accurate diagnostic process. Clinical diagnosis of DSD is limited by a lack of standardization of anatomical and endocrine phenotyping and genetic testing, as well as poor genotype/phenotype correlation. Historically, DSD genes have been identified through positional cloning of disease-associated variants segregating in families and validation of candidates in animal and in vitro modeling of variant pathogenicity. Owing to the complexity of conditions grouped under DSD, genome-wide scanning methods are better suited for identifying disease causing gene variant(s) and providing a clinical diagnosis. Here, we review a number of established genomic tools (karyotyping, chromosomal microarrays and exome sequencing) used in clinic for DSD diagnosis, as well as emerging genomic technologies such as whole-genome (short-read) sequencing, long-read sequencing, and optical mapping used for novel DSD gene discovery. These, together with gene expression and epigenetic studies can potentiate the clinical diagnosis of DSD diagnostic rates and enhance the outcomes for patients and families.

At the Crossroads of Fate-Somatic Cell Lineage Specification in the Fetal Gonad

The reproductive endocrine systems are vastly different between males and females. This sexual dimorphism of the endocrine milieu originates from sex-specific differentiation of the somatic cells in the gonads during fetal life. Most gonadal somatic cells arise from the adrenogonadal primordium. After separation of the adrenal and gonadal primordia, the gonadal somatic cells initiate sex-specific differentiation during gonadal sex determination with the specification of the supporting cell lineages: Sertoli cells in the testis vs granulosa cells in the ovary. The supporting cell lineages then facilitate the differentiation of the steroidogenic cell lineages, Leydig cells in the testis and theca cells in the ovary. Proper differentiation of these cell types defines the somatic cell environment that is essential for germ cell development, hormone production, and establishment of the reproductive tracts. Impairment of lineage specification and function of gonadal somatic cells can lead to disorders of sexual development (DSDs) in humans. Human DSDs and processes for gonadal development have been successfully modeled using genetically modified mouse models. In this review, we focus on the fate decision processes from the initial stage of formation of the adrenogonadal primordium in the embryo to the maintenance of the somatic cell identities in the gonads when they become fully differentiated in adulthood.

GENETICS IN ENDOCRINOLOGY: Approaches to molecular genetic diagnosis in the management of differences/disorders of sex development (DSD): position paper of EU COST Action BM 1303 ‘DSDnet’

The differential diagnosis of differences or disorders of sex development (DSD) belongs to the most complex fields in medicine. It requires a multidisciplinary team conducting a synoptic and complementary approach consisting of thorough clinical, hormonal and genetic workups. This position paper of EU COST (European Cooperation in Science and Technology) Action BM1303 ‘DSDnet’ was written by leading experts in the field and focuses on current best practice in genetic diagnosis in DSD patients. Ascertainment of the karyotpye defines one of the three major diagnostic DSD subclasses and is therefore the mandatory initial step. Subsequently, further analyses comprise molecular studies of monogenic DSD causes or analysis of copy number variations (CNV) or both. Panels of candidate genes provide rapid and reliable results. Whole exome and genome sequencing (WES and WGS) represent valuable methodological developments that are currently in the transition from basic science to clinical routine service in the field of DSD. However, in addition to covering known DSD candidate genes, WES and WGS help to identify novel genetic causes for DSD. Diagnostic interpretation must be performed with utmost caution and needs careful scientific validation in each DSD case.

Novel Familial Variant of the Desert Hedgehog Gene: Clinical Findings in Two Sisters with 46,XY Gonadal Dysgenesis or 46,XX Karyotype and Literature Review

BACKGROUND

In humans, Desert Hedgehog (DHH) gene mutations are a very rare cause of 46,XY gonadal dysgenesis (GD), eventually associated with peripheral neuropathy.

PATIENTS AND METHODS

Clinical records of 12 patients with 46,XY GD and unknown genetic background were reviewed and a 46,XY woman with peripheral neuropathy was individuated. Her 46,XX sister affected by similar neuropathy was also investigated. Genomic DNA was extracted and DHH exons sequenced and analyzed. A comparative genomic hybridization array was also performed.

RESULTS

In both the 46,XY and 46,XX sisters, a homozygous c.554C>A mutation in exon 2 of the DHH gene was found, determining a premature termination codon (p.Ser 185*). Heterozygous consanguineous carrier parents showed neither reproductive problems nor peripheral neuropathy. In the proband and her sister, a 499-kb duplication in 9p22.1 was also found.

CONCLUSION

A 46,XY European woman with 46,XY GD and a novel homozygous DHH pathogenic variant is reported, confirming that this gene plays a key role in male gonadal development. Her 46,XX sister, harboring the same mutation, showed normal internal and external female phenotype. Thus, DHH seems not to be involved in the ovarian development pathway or its postpubertal function. Homozygous DHH mutations cause a specific peripheral neuropathy in humans with both 46,XY and 46,XX karyotypes.

A Case of Two Sisters Suffering from 46,XY Gonadal Dysgenesis and Carrying a Mutation of a Novel Candidate Sex-Determining Gene STARD8 on the X Chromosome

Identification of novel genes involved in sexual development is crucial for understanding disorders of sex development (DSD). Here, we propose a member of the START domain family, the X chromosome STARD8, as a DSD candidate gene. We have identified a missense mutation of this gene in 2 sisters with 46,XY gonadal dysgenesis, inherited from their heterozygous mother. Gonadal tissue of one of the sisters contained Leydig cells overloaded with cholesterol droplets, i.e., structures previously identified in 46,XY DSD patients carrying mutations in the STAR gene encoding another START domain family member, which is crucial for steroidogenesis. Based on the phenotypes of our patients, we propose a dual role of STARD8 in sexual development, namely in testes determination and testosterone synthesis. However, further studies are needed to confirm the involvement of STARD8 in sexual development.

Stromal Gli signaling regulates the activity and differentiation of prostate stem and progenitor cells

Interactions between cells in the stroma and epithelium facilitate prostate stem cell activity and tissue regeneration capacity. Numerous molecular signal transduction pathways, including the induction of sonic hedgehog (Shh) to activate the Gli transcription factors, are known to mediate the cross-talk of these two cellular compartments. However, the details of how these signaling pathways regulate prostate stem and progenitor cell activity remain elusive. Here we demonstrate that, although cell-autonomous epithelial Shh-Gli signaling is essential to determine the expression levels of basal cell markers and the renewal potential of epithelial stem and progenitor cells, stromal Gli signaling regulates prostate stem and progenitor cell activity by increasing the number and size of prostate spheroids in vitro Blockade of stromal Gli signaling also inhibited prostate tissue regeneration in vivo The inhibition of stromal Gli signaling suppressed the differentiation of basal and progenitor cells to luminal cells and limited prostate tubule secretory capability. Additionally, stromal cells were able to compensate for the deficiency of epithelial Shh signaling in prostate tissue regeneration. Mechanistically, suppression of Gli signaling increased the signaling factor transforming growth factor β (TGFβ) in stromal cells. Elevation of exogenous TGFβ1 levels inhibited prostate spheroid formation, suggesting that a stromal Gli-TGFβ signaling axis regulates the activity of epithelial progenitor cells. Our study illustrates that Gli signaling regulates epithelial stem cell activity and renewal potential in both epithelial and stromal compartments.

Effects of the insulin-like growth factor system on testicular differentiation and function: a review of the literature

We recently described the occurrence of cryptorchidism, oligoasthenoteratozoospermia, and genital abnormalities in patients with distal 15q chromosome structural abnormalities. This observation brought us to hypothesize that insulin-like growth factor (IGF) receptor (IGF1R), mapping on the 15q 26.3 chromosomal band, may be involved in testicular function. To further evaluate this topic, we reviewed in vitro and in vivo studies exploring the role of the IGF system [IGF1, IGF2, IGF1R, insulin receptor substrates (IRS)] at the testicular level both in animals and in humans. In animals, IGF1/IGF1R has been found to be involved in testicular development during embryogenesis, in Sertoli cell (SC) proliferation, and in germ cell (GS) proliferation and differentiation. Interestingly, IGF1R seems to mediate follicle-stimulating hormone (FSH) effects through the PI3K/AKT pathway. In humans, IGF1 directly increases testicular volume. The molecular pathways responsible for testicular differentiation and IGF1/IGF1R signaling are highly conserved among species; therefore, the IGF system may be involved in FSH signaling also in humans. We suggest a possible molecular pathway occurring in human SCs, which involves both IGF1 and FSH through the PI3K/AKT pathway. The acknowledgment of an IGF1 mediation of the FSH-induced effects may open new ways for a targeted therapy in idiopathic non-FSH-responder oligoasthenoteratozoospermia.

In mammalian foetal testes, SOX9 regulates expression of its target genes by binding to genomic regions with conserved signatures

In mammalian embryonic gonads, SOX9 is required for the determination of Sertoli cells that orchestrate testis morphogenesis. To identify genetic networks directly regulated by SOX9, we combined analysis of SOX9-bound chromatin regions from murine and bovine foetal testes with sequencing of RNA samples from mouse testes lacking Sox9. We found that SOX9 controls a conserved genetic programme that involves most of the sex-determining genes. In foetal testes, SOX9 modulates both transcription and directly or indirectly sex-specific differential splicing of its target genes through binding to genomic regions with sequence motifs that are conserved among mammals and that we called ‘Sertoli Cell Signature’ (SCS). The SCS is characterized by a precise organization of binding motifs for the Sertoli cell reprogramming factors SOX9, GATA4 and DMRT1. As SOX9 biological role in mammalian gonads is to determine Sertoli cells, we correlated this genomic signature with the presence of SOX9 on chromatin in foetal testes, therefore equating this signature to a genomic bar code of the fate of foetal Sertoli cells. Starting from the hypothesis that nuclear factors that bind to genomic regions with SCS could functionally interact with SOX9, we identified TRIM28 as a new SOX9 partner in foetal testes.

Yeast Gup1(2) Proteins Are Homologues of the Hedgehog Morphogens Acyltransferases HHAT(L): Facts and Implications

In multiple tissues, the Hedgehog secreted morphogen activates in the receiving cells a pathway involved in cell fate, proliferation and differentiation in the receiving cells. This pathway is particularly important during embryogenesis. The protein HHAT (Hedgehog O-acyltransferase) modifies Hh morphogens prior to their secretion, while HHATL (Hh O-acyltransferase-like) negatively regulates the pathway. HHAT and HHATL are homologous to Saccharomyces cerevisiae Gup2 and Gup1, respectively. In yeast, Gup1 is associated with a high number and diversity of biological functions, namely polarity establishment, secretory/endocytic pathway functionality, vacuole morphology and wall and membrane composition, structure and maintenance. Phenotypes underlying death, morphogenesis and differentiation are also included. Paracrine signalling, like the one promoted by the Hh pathway, has not been shown to occur in microbial communities, despite the fact that large aggregates of cells like biofilms or colonies behave as proto-tissues. Instead, these have been suggested to sense the population density through the secretion of quorum-sensing chemicals. This review focuses on Gup1/HHATL and Gup2/HHAT proteins. We review the functions and physiology associated with these proteins in yeasts and higher eukaryotes. We suggest standardisation of the presently chaotic Gup-related nomenclature, which includes KIAA117, c3orf3, RASP, Skinny, Sightless and Central Missing, in order to avoid the disclosure of otherwise unnoticed information.

The role of next generation sequencing in understanding male and female sexual development: clinical implications

Next Generation Sequencing is revolutionising our understanding of variation in the human genome and as costs reduce the sequencing of patient's genomes is become more routine. Areas covered: Here, we review the current challenges in the field and some of the efforts that are underway to resolve them. We describe how these technologies are impacting on our understanding of human sex development and the profound clinical implications of these technologies on conditions such as Disorders of Sex Development (DSD). Expert commentary: The sheer wealth of genomic data is generating new challenges-some are technical such as variant calling, or predicting the functional consequence of a variant-whereas others are more profound, such as establishing the link between extensive genomic information and the clinical presentation. Predicting disease phenotypes from genetic sequences is often extremely difficult because the genotype-phenotype relationship has proven to be far more complex than anticipated.

Signaling Pathways Involved in Mammalian Sex Determination and Gonad Development

The development of any organ system requires a complex interplay of cellular signals to initiate the differentiation and development of the heterogeneous cell and tissue types required to carry out the organs' functions. In this way, an extracellular stimulus is transmitted to an intracellular target through an array of interacting protein intermediaries, ultimately enabling the target cell to elicit a response. Surprisingly, only a small number of signaling pathways are implicated throughout embryogenesis and are used over and over again. Gonadogenesis is a unique process in that 2 morphologically distinct organs, the testes and ovaries, arise from a common precursor, the bipotential genital ridge. Accordingly, most of the signaling pathways observed throughout embryogenesis also have been shown to be important for mammalian sex determination and gonad development. Here, we review the mechanisms of signal transduction within these pathways and the importance of these pathways throughout mammalian gonad development, mainly concentrating on data obtained in mouse but including other species where appropriate.

Overview of genetics of disorders of sexual development

PURPOSE OF REVIEW

Disorders of sexual development (DSD) are a genetic and phenotypic heterogeneous group of congenital disorders. This review focuses on the genetics of DSD and aims to recognize and contextualize, in a systematic way, based on the classification and the genetic mechanisms, the latest developments in the field of DSD diagnostics.

RECENT FINDINGS

Due to the current diagnostic armamentarium, during the past decade, the field of DSD diagnostics has changed dramatically from the recognition of few genes and cytogenetic abnormalities, to the identification of multiple genes and a wide arrange of genetic mechanisms involved in the genesis of DSD. In addition, the phenotypes associated with the genetic mechanism have expanded tremendously.

SUMMARY

Despite the current diagnostic limitations, the landscape for genetics of DSD is encouraging due to discovery of new genes, their interactions, and the recognition of the variety of mechanisms involved.

Disorders of sex development: effect of molecular diagnostics

Disorders of sex development (DSDs) are a diverse group of conditions that can be challenging to diagnose accurately using standard phenotypic and biochemical approaches. Obtaining a specific diagnosis can be important for identifying potentially life-threatening associated disorders, as well as providing information to guide parents in deciding on the most appropriate management for their child. Within the past 5 years, advances in molecular methodologies have helped to identify several novel causes of DSDs; molecular tests to aid diagnosis and genetic counselling have now been adopted into clinical practice. Occasionally, genetic profiling of embryos prior to implantation as an adjunct to assisted reproduction, prenatal diagnosis of at-risk pregnancies and confirmatory testing of positive results found during newborn biochemical screening are performed. Of the available genetic tests, the candidate gene approach is the most popular. New high-throughput DNA analysis could enable a genetic diagnosis to be made when the aetiology is unknown or many differential diagnoses are possible. Nonetheless, concerns exist about the use of genetic tests. For instance, a diagnosis is not always possible even using new molecular approaches (which can be worrying for the parents) and incidental information obtained during the test might cause anxiety. Careful selection of the genetic test indicated for each condition remains important for good clinical practice. The purpose of this Review is to describe advances in molecular biological techniques for diagnosing DSDs.

46,XY Gonadal Dysgenesis due to a Homozygous Mutation in Desert Hedgehog (DHH) Identified by Exome Sequencing

BACKGROUND

46,XY disorders of sex development (DSD) comprise a heterogeneous group of congenital conditions. Mutations in a variety of genes can affect gonadal development or androgen biosynthesis/action and thereby influence the development of the internal and external genital organs.

OBJECTIVE

The objective of the study was to identify the genetic cause in two 46,XY sisters of a consanguineous family with DSD and gonadal tumor formation.

METHODS

We used a next-generation sequencing approach by exome sequencing. Electrophysiological and high-resolution ultrasound examination of peripheral nerves as well as histopathological examination of the gonads were performed.

RESULTS

We identified a novel homozygous R124Q mutation in the desert hedgehog gene (DHH), which alters a conserved residue among the three mammalian Hedgehog ligands sonic hedgehog, Indian hedgehog, and desert hedgehog. No other relevant mutations in DSD-related genes were encountered. The gonads of one patient showed partial gonadal dysgenesis with loss of Leydig cells in tubular areas with seminoma in situ and a hyperplasia of Leydig cell-like cells expressing CYP17A1 in more dysgenetic parts of the gonad. In addition, both patients suffer from a polyneuropathy. High-resolution ultrasound revealed a structural change of peripheral nerve structure that fits well to a minifascicle formation of peripheral nerves.

CONCLUSION

Mutations in DHH play a role in 46,XY gonadal dysgenesis and are associated with seminoma formation and a neuropathy with minifascicle formation. Gonadal dysgenesis in these cases may be due to impairment of Sertoli cell-Leydig cell interaction during gonadal development.

Hedgehog signaling: From basic research to clinical applications

Studies of the major signaling pathways have revealed a connection between development, regeneration, and cancer, highlighting common signaling networks in these processes. The Hedgehog (Hh) pathway plays a central role in the development of most tissues and organs in mammals. Hh signaling is also required for tissue homeostasis and regeneration in adults, while perturbed Hh signaling is associated with human cancers. A fundamental understanding of Hh signaling will not only enhance our knowledge of how the embryos are patterned but also provide tools to treat diseases related to aberrant Hh signaling. Studies have yielded a basic framework of Hh signaling, which establishes the foundation for addressing unresolved issues of Hh signaling. A detailed characterization of the biochemical interactions between Hh components will help explain the production of graded Hh responses required for tissue patterning. Additional cell biological and genetic studies will offer new insight into the role of Hh signaling in homeostasis and regeneration. Finally, drugs that are capable of manipulating the Hh pathway can be used to treat human diseases caused by disrupted Hh signaling. These investigations will serve as a paradigm for studying signal transduction/integration in homeostasis and disease, and for translating discovery from bench to bedside.

Palmitoylation and depalmitoylation defects

Palmitoylation describes the enzymatic attachment of a 16-carbon atom fatty acid to a target protein. Such lipidation events occur in all eukaryotes and can be of reversible (S-palmitoylation) or irreversible (N-palmitoylation) nature. In particular S-palmitoylation is dynamically regulated by two opposing types of enzymes which add (palmitoyl acyltransferases - PAT) or remove (acyl protein thioesterases) palmitate from proteins. Protein palmitoylation is an important process that dynamically regulates the assembly and compartmentalization of many neuronal proteins at specific subcellular sites. Enzymes that regulate protein palmitoylation are critical for several biological processes. To date, eight palmitoylation related genes have been reported to be associated with human disease. This review intends to give an overview on the pathological changes which are associated with defects in the palmitoylation/depalmitoylation process.

Genetic regulation of mammalian gonad development

Sex-specific gonadal development starts with formation of the bipotential gonad, which then differentiates into either a mature testis or an ovary. This process is dependent on activation of either the testis-specific or the ovary-specific pathway while the opposite pathway is continuously repressed. A network of transcription factors tightly regulates initiation and maintenance of these distinct pathways; disruption of these networks can lead to disorders of sex development in humans and male-to-female or female-to-male sex reversal in mice. Sry is the Y-linked master switch that is both required and sufficient to drive the testis-determining pathway. Another key component of the testis pathway is Sox9, which acts immediately downstream of Sry. In contrast to the testis pathway, no single sex-determining factor has been identified in the ovary pathway; however, multiple genes, such as Foxl2, Rspo1, Ctnnb1, and Wnt4, seem to work synergistically and in parallel to ensure proper ovary development. Our understanding of the regulatory networks that underpin testis and ovary development has grown substantially over the past two decades.

DSDs: genetics, underlying pathologies and psychosexual differentiation

Mammalian sex determination is the unique process whereby a single organ, the bipotential gonad, undergoes a developmental switch that promotes its differentiation into either a testis or an ovary. Disruptions of this complex genetic process during human development can manifest as disorders of sex development (DSDs). Sex development can be divided into two distinct processes: sex determination, in which the bipotential gonads form either testes or ovaries, and sex differentiation, in which the fully formed testes or ovaries secrete local and hormonal factors to drive differentiation of internal and external genitals, as well as extragonadal tissues such as the brain. DSDs can arise from a number of genetic lesions, which manifest as a spectrum of gonadal (gonadal dysgenesis to ovotestis) and genital (mild hypospadias or clitoromegaly to ambiguous genitalia) phenotypes. The physical attributes and medical implications associated with DSDs confront families of affected newborns with decisions, such as gender of rearing or genital surgery, and additional concerns, such as uncertainty over the child's psychosexual development and personal wishes later in life. In this Review, we discuss the underlying genetics of human sex determination and focus on emerging data, genetic classification of DSDs and other considerations that surround gender development and identity in individuals with DSDs.

The emerging role of insulin-like growth factors in testis development and function

The insulin-like family of growth factors (IGFs) - composed of insulin, and insulin-like growth factors I (IGF1) and II (IGF2) - provides essential signals for the control of testis development and function. In the testis, IGFs act in an autocrine-paracrine manner but the extent of their actions has been underestimated due to redundancies at both the ligand and receptor levels, and the perinatal lethality of constitutive knockout mice. This review synthesizes the current understanding of how the IGF system regulates biological processes such as primary sex determination, testis development, spermatogenesis and steroidogenesis, and highlights the questions that remain to be explored.