SOX10 Mutations Research Articles

Discrepancy between macroscopic and microscopic transitional zones in Hirschsprung's disease with reference to the type of RET/GDNF/SOX10 gene mutation

Background/Purpose: Recent studies have found that Hirschsrung's disease is caused by diverse genomic abnormalities. To clarifiy whether these pathogenic variations influence the distribution and function of enteric ganglia, the authors studied the morphology of the macroscopic and microscopic transitional zone in Hirschsprung's disease with reference to the type of genetic mutation. Methods: In 120 patients with Hirschsprung's disease, the location and morphology of the gut caliber change were recorded, and the enteric nervous system was investigated histologically using biopsy specimens. The DNA sequences of all the RET/GDNF/NTN and SOX10 coding regions were determined using the direct DyeDeoxy Terminator Cycle method. Results: In RET mutation carriers, the gut caliber change was almost identical to the histologic transition in cases of short segment aganglionosis, whereas these were markedly dissociated in cases exhibiting extensive aganglionosis. In contrast, SOX10 mutation carriers had a very long histologic transition and exhibited no caliber change. Conclusions: The type of genetic mutation responsible for Hirschsprung's disease influences the postnatal distribution and function of enteric ganglia. The data on discrepancy between macroscopic and microscopic transitions may enable us to concentrate the sites of the leveling biopsy more accurately especially in cases of long type intestinal aganglionosis carrying RET gene mutation. J Pediatr Surg 38:698-701. © 2003 Elsevier Inc. All rights reserved.

Sox10 and Pax3 physically interact to mediate activation of a conserved c-RET enhancer.

The neurocristopathies encompass a spectrum of developmental disorders characterized by abnormalities of neural crest-derived structures. Neural crest cells are pluripotent progenitors and the mechanisms by which specific cell-fate decisions are regulated have emerged as an important field of study. Many neurocristopathies are characterized by defects in melanocyte differentiation that can result in pigmentation abnormalities and deafness. One example is Waardenburg syndrome that can be caused by mutations in the PAX3, SOX10 or MITF genes. Other neural crest-related disorders are associated with enteric ganglia defects, such as those caused by mutations in the SOX10 or c-RET genes. The Pax3 and Sox10 transcription factors can directly regulate both MITF and c-RET. Here, we show that Pax3 and Sox10 can physically interact and we map the interaction domains. We show that this interaction contributes to Pax3 and Sox10 synergistic activation of a conserved c-RET enhancer and it explains why Sox10 mutants that cannot bind to DNA retain the ability to activate this enhancer in the presence of Pax3. However, in the context of the MITF gene, Pax3 and Sox10 must each bind independently to DNA in order to achieve synergy. This difference is consistent with the different structures of the c-RET and MITF enhancers, and the different mechanisms by which Pax3 binds to these enhancers. These observations explain the phenotype in the mild form of Yemenite deaf-blind syndrome caused by specific SOX10 mutations in the HMG box that abrogate DNA binding without disrupting association with Pax3.

Mutations in SOX2 cause anophthalmia

A submicroscopic deletion containing SOX2 was identified at the 3q breakpoint in a child with t(3;11)(q26.3;p11.2) associated with bilateral anophthalmia. Subsequent SOX2 mutation analysis identified de novo truncating mutations of SOX2 in 4 of 35 (11%) individuals with anophthalmia. Both eyes were affected in all cases with an identified mutation.

Sox10 haploinsufficiency affects maintenance of progenitor cells in a mouse model of Hirschsprung disease.

Hirschsprung disease, or congenital megacolon, is characterized by aganglionosis of the terminal bowel, which leads to intestinal obstruction and chronic constipation. Several genes involved in the disease have been identified. In particular, haploinsufficiency of SOX10, which encodes a transcription factor, results in megacolon, often in combination with other disorders. Although Hirschsprung disease has been recognized as a neurocristopathy, the cellular mechanisms that lead to aganglionosis in affected individuals are unclear. Failure of mutant enteric progenitor cells to migrate into the gut, to survive, or to differentiate into appropriate cell types at the appropriate time and in correct numbers might contribute to the disease phenotype. In the present study, we use mice with a targeted deletion of Sox10 to study the etiology of Hirschsprung disease. We demonstrate that neural crest-derived enteric progenitors that are heterozygous for the Sox10 mutation colonize the proximal intestine and are unaffected in their survival capacity. However, unlike their wild-type counterparts, mutant enteric neural crest-derived cells are unable to maintain their progenitor state and acquire preneuronal traits, which results in a reduction of the progenitor pool size. Thus, the cells that normally colonize the hindgut are depleted in the Sox10 mutant, causing the distal bowel to become aganglionic.

Migration and Function of a Glial Subtype in the Vertebrate Peripheral Nervous System

Glia-axon interactions are essential for the development and function of the nervous system. We combine in vivo imaging and genetics to address the mechanism by which the migration of these cells is coordinated during embryonic development. Using stable transgenic lines, we have followed the migration of one subset of glial cells and their target axons in living zebrafish embryos. These cells coalesce at an early stage and remain coupled throughout migration, with axons apparently pathfinding for glia. Mutant analysis demonstrates that axons provide instructive cues that are sufficient to control glial guidance. Furthermore, mutations in the transcription factor Sox10/ cls uncouple the migration of axons and glia. Finally, genetic ablation of this glial subtype reveals an essential role in nerve fasciculation.

Segregation at three loci explains familial and population risk in Hirschsprung disease

Hirschsprung disease (HSCR), the most common hereditary cause of intestinal obstruction, shows considerable variation and complex inheritance. Coding sequence mutations in RET, GDNF, EDNRB, EDN3 and SOX10 lead to long-segment (L-HSCR) and syndromic HSCR but fail to explain the transmission of the much more common short-segment form (S-HSCR). We conducted a genome scan in families with S-HSCR and identified susceptibility loci at 3p21, 10q11 and 19q12 that seem to be necessary and sufficient to explain recurrence risk and population incidence. The gene at 10q11 is probably RET, supporting its crucial role in all forms of HSCR; however, coding sequence mutations are present in only 40% of linked families, suggesting the importance of noncoding variation. Here we show oligogenic inheritance of S-HSCR, the 3p21 and 19q12 loci as RET-dependent modifiers, and a parent-of-origin effect at RET. This study demonstrates by a complete genetic dissection why the inheritance pattern of S-HSCR is nonmendelian.

Regulation of the orphan nuclear receptor steroidogenic factor 1 by Sox proteins.

Steroidogenic factor 1 (SF-1) is an essential factor in endocrine proliferation and gene expression. Despite the fact that SF-1 expression is restricted to specialized cells within the endocrine system, the only identified regulatory factors of SF-1 are the ubiquitously expressed E-box proteins (upstream stimulatory factors 1 and 2). Sequence examination of the SF-1 proximal promoter revealed a conserved site of AACAAAG (Sox-BS1), which matches exactly the defined consensus Sox protein binding element. Among the approximately 20 known members of the Sox gene family, we focused on Sox3, Sox8, and Sox9, based on their coexpression with SF-1 in the embryonic testis. Indeed, all three of these Sox proteins were capable of binding the proximal Sox-BS1 within the SF-1 promoter (-110 to -104), albeit with differing affinities. Of the three Sox proteins, Sox9 exhibited high-affinity binding to the Sox-BS1 element and consistently activated SF-1 promoter-reporter constructs. Mutating the Sox-BS1 attenuated SF-1 promoter activity in both embryonic and postnatal Sertoli cells, as well as in the adrenocortical cell line, Y1. Our findings, taken together with the overlapping expression profiles of Sox9 and SF-1, and the similar intersex phenotypes associated with both SOX9 and SF-1 human mutations, suggest that Sox9 up-regulates SF-1 and accounts partially for the sexually dimorphic expression pattern of SF-1 observed during male gonadal differentiation.

Conditional inactivation of Sox9: a mouse model for campomelic dysplasia.

Campomelic dysplasia (CD), a semilethal human skeletal malformation syndrome with XY sex reversal, is caused by heterozygous mutations in the SRY-related transcription factor gene SOX9 (Foster et al., 1994; Wagner et al., 1994). The mouse Sox9 gene, located on distal chromosome 11, is expressed during chondrogenesis (Wright et al., 1995), and is a key regulator of cartilage differentiation (Bi et al., 1999) and testis development (Vidal et al., 2001). Sox9 is expressed in a variety of embryonic tissues (Ng et al., 1997), suggesting further functions for Sox9/SOX9 during organogenesis. Indeed, CD patients show malformations in nonskeletal organs such as brain, heart, and kidneys (Houston et al., 1983; Mansour et al., 1995). Recently, Sox9 / mutant mice have been generated by a classical gene targeting approach and were shown to phenocopy the skeletal malformations observed in CD (Bi et al., 2001). However, because Sox9 / mice die shortly after birth, it was not possible to generate a stable Sox9 mutant mouse line. To circumvent this problem and to provide a tool for an in-depth analysis of Sox9 functions in skeletal development and the formation of other organs, we have generated a conditional Sox9 mutant allele in mice using the Cre/loxP system (Nagy, 2000; Le and Sauer, 2001) (Fig.1). Five correctly targeted embryonic stem (ES) cell clones were identified, and, following successful deletion of the neo cassette by transient in vitro expression of Cre recombinase (Taniguchi et al., 1998), two clones were microinjected into C57BL/6 blastocysts. Germline transmission was obtained for both clones and two Sox9-flox mouse lines have been established by backcrossing to C57BL/6 mice. Both Sox9 homozygous male and female mice are viable and fertile and do not show any obvious phenotype. To test for conditional inactivation of Sox9 in vivo, Sox9 /flox mice were crossed to Cre deleter mice which ubiquitously express the Cre recombinase (Schwenk et al., 1995) (Fig 2a). In Sox9 ; Cre–transgenic animals, designated as Sox9 / , exon 2 encoding half of the DNA-binding high-mobility group (HMG) domain and exon 3 encoding the entire transactivation domain are deleted (Fig. 2a, b). Because the transactivation domain is essential for SOX9 function (Sudbeck et al., 1996), and because truncated HMG domains cannot bind to DNA (Giese et al., 1991), our strategy most likely results in a functional null allele of the Sox9 gene. Complete recombination of the loxP-flanked Sox9 allele was demonstrated by allele-specific PCR analysis of Sox9 / mutants (Fig. 2c). Sox9 / mice died shortly after birth, presumably because of severe respiratory failure caused by a cleft secondary palate. Skeletal staining of newborn Sox9 / mutants revealed bone malformations typically observed in CD patients (Fig. 2 and data not shown). For example, the scapula was hypoplastic and malformed and the deltoid tuberosity of the humerus was missing (Fig. 2e). In addition, premature mineralization occurred in many skeletal elements, including the tail vertebrae (Fig. 2g). This is in agreement with the recently proposed role for Sox9 in regulating the rate of hypertrophic chondrocyte differentiation (Bi et al., 2001). Taken together, our analysis revealed that the skeletal phenotype of conditional Sox9 / mutants is very similar to that described for Sox9 / mutants (Bi et al., 2001). The different genetic background of mice used in the two studies may account for minor differences we observed in the severity of the skeletal phenotypes. The availability of tissue-specific or inducible Cre-transgenic mouse strains will make the conditional Sox9 allele a valuable tool not only to understand cartilage differentiation and skeletogenesis but also to investigate Sox9 functions during the development of a variety of other organs during mammalian development.

The transcription factor Sox9 is required for cranial neural crest development inXenopus

The SOX family of transcription factors has been implicated in cell fate specification during embryogenesis. One member of this family, Sox9, has been shown to regulate both chondrogenesis and sex determination in the mouse embryo. Heterozygous mutations in Sox9 result in Campomelic Dysplasia (CD), a lethal human disorder characterized by autosomal XY sex reversal, severe skeletal malformations and several craniofacial defects. Sox9 is also expressed in neural crest progenitors but very little is known about the function of Sox9 in the neural crest. We have cloned the Xenopus homolog of the Sox9 gene. It is expressed maternally and accumulates shortly after gastrulation at the lateral edges of the neural plate, in the neural crest-forming region. As development proceeds, Sox9 expression persists in migrating cranial crest cells as they populate the pharyngeal arches. Depletion of Sox9 protein in developing embryos, using morpholino antisense oligos, causes a dramatic loss of neural crest progenitors and an expansion of the neural plate. Later during embryogenesis, morpholino-treated embryos have a specific loss or reduction of neural crest-derived skeletal elements, mimicking one aspect of the craniofacial defects observed in CD patients. We propose that Sox9 is an essential component of the regulatory pathway that leads to cranial neural crest formation.

Human Connexin 32, a gap junction protein altered in the X-linked form of Charcot-Marie-Tooth disease, is directly regulated by the transcription factor SOX10.

Mutations in SOX10, a transcription modulator crucial in the development of the enteric nervous system (ENS), melanocytes and glial cells, are found in Shah-Waardenburg syndrome (WS4), a neurocristopathy that associates intestinal aganglionosis, pigmentation defects and sensorineural deafness. Expression of MITF and RET, two genes that play important roles during melanocyte and ENS development, respectively, are controlled by SOX10. The observation that some WS4 patients present with myelination defects of the central and peripheral nervous systems correlates with the recent finding that P(0), a major component of the peripheral myelin, is another transcriptional target of SOX10. These phenotypic features suggest that SOX10 could regulate expression of other genes involved in the myelination process as well. Thus, we tested the ability of SOX10 to regulate expression of MBP, PMP22 and Connexin 32, three major proteins of the peripheral myelin. Our study shows that this factor, in synergy with EGR2, strongly activates Cx32 expression in vitro by directly binding to its promoter. In agreement with this finding, SOX10 and EGR2 mutants identified in patients with peripheral myelin defects fail to transactivate the Cx32 promoter. Moreover, we show that a mutation of the Cx32 promoter previously described in a patient with the X-linked form of Charcot-Marie-Tooth (CMTX) disease impairs SOX10 function. In addition to providing new insights into the molecular mechanisms underlying some of the peripheral myelin defects observed in CMTX disease, these results further extend the spectrum of genes that are regulated by SOX10.

Relationship between the type of RET/GDNF/NTN or SOX10 gene mutations and long-term results after surgery for total colonic aganglionosis with small bowel involvement

Background/Purpose: Germline mutations of the RET-mediated or SOX10-mediated signaling pathway genes have been reported in total colonic aganglionosis (TCA). The authors investigated the possible relationship between the type of such genomic abnormalities and surgical outcomes. Methods: Sixteen patients with TCA with extensive small bowel involvement were studied. DNA sequences of all the RET/GDNF/NTN and SOX10 coding regions were determined by the direct DyeDeoxy Terminator Cycle method. Data on the patients' clinical courses were obtained retrospectively from their medical charts and surgical records. Results:RET or SOX10 germline mutations were identified in 11 of the 16 patients (68.8%). In children with aganglionosis up to the jejunum or ileum, most grew up within normal ranges, and the frequency of bowel movements decreased to 2 to 4 times per day within 5 years. However, in 5 infants with total intestinal aganglionosis, only 2 survived beyond 2 years of age, both of whom underwent Ziegler's myectomy-myotomy. A SOX10 mutation was identified in an infant with Shah-Waardenburg's syndrome, and he showed persistent bowel malfunction. Conclusion: The existence or type of RET mutation usually did not affect surgical results in this series of TCA patients, whereas the mutational analysis suggested 2 disease categories of TCA showing different postoperative courses, which may reflect the disparate pathogenesis in the enteric nervous system development induced by impaired RET or SOX10 signaling pathway. J Pediatr Surg 36:1685-1688. Copyright © 2001 by W.B. Saunders Company.

Survival and glial fate acquisition of neural crest cells are regulated by an interplay between the transcription factor Sox10 and extrinsic combinatorial signaling.

The transcription factor Sox10 is required for proper development of various neural crest-derived cell types. Several lineages including melanocytes, autonomic and enteric neurons, and all subtypes of peripheral glia are missing in mice homozygous for Sox10 mutations. Moreover, haploinsufficiency of Sox10 results in neural crest defects that cause Waardenburg/Hirschsprung disease in humans. We provide evidence that the cellular basis to these phenotypes is likely to be a requirement for Sox10 by neural crest stem cells before lineage segregation. Cell death is increased in undifferentiated, postmigratory neural crest cells that lack Sox10, suggesting a role of Sox10 in the survival of neural crest cells. This function is mediated by neuregulin, which acts as a survival signal for postmigratory neural crest cells in a Sox10-dependent manner. Furthermore, Sox10 is required for glial fate acquisition, as the surviving mutant neural crest cells are unable to adopt a glial fate when challenged with different gliogenic conditions. In Sox10 heterozygous mutant neural crest cells, survival appears to be normal, while fate specifications are drastically affected. Thereby, the fate chosen by a mutant neural crest cell is context dependent. Our data indicate that combinatorial signaling by Sox10, extracellular factors such as neuregulin 1, and local cell-cell interactions is involved in fine-tuning lineage decisions by neural crest stem cells. Failures in fate decision processes might thus contribute to the etiology of Waardenburg/Hirschsprung disease.

SOX10 is abnormally expressed in aganglionic bowel of Hirschsprung's disease infants

BACKGROUNDThe primary pathology of Hirschsprung's disease (HD) is a congenital absence of ganglion cells in the caudal most gut. The spastic aganglionic bowel is often innervated by a network of...

L-Sox5, Sox6 and Sox9 control essential steps of the chondrocyte differentiation pathway

Objective This work was carried out to identify transcription factors controlling the differentiation of mesenchymal cells into chondrocytes. Design We delineated a cartilage-specific enhancer in the collagen type 2 gene (Col2a1) and identified transcription factors responsible for the activity of this enhancer in chondrocytes. We then analyzed the ability of these transcription factors to activate specific genes of the chondrocyte differentiation program and control cartilage formation in vivo. Results A 48-bp sequence in the first intron of Col2a1 drove gene expression specifically in cartilage in transgenic mouse embryos. The transcription factors L-Sox5, Sox6, and Sox9 bound and cooperatively activated this enhancer in vitro. They belong to the Sry-related family of HMG box DNA-binding proteins, which includes many members implicated in cell fate determination in various lineages. L-Sox5, Sox6, and Sox9 were coexpressed in all precartilaginous condensations in mouse embryos and continued to be expressed in chondrocytes until the cells underwent final hypertrophy. Whereas L-Sox5 and Sox6 are highly homologous proteins, they are totally different from Sox9 outside the HMG box domain. The three proteins cooperatively activated the Col2a1- and aggrecan genes in cultured cells. Heterozygous mutations in SOX9 in humans lead to campomelic dysplasia, a severe and generalized skeletal malformation syndrome. Embryonic cells with a homozygous Sox9 mutation were unable to form cartilage in vivo and activate essential chondrocyte marker genes. Preliminary data indicated that the mutation of Sox5 and Sox6 in the mouse led to severe skeletal malformations. Conclusions L-Sox5, Sox6, and Sox9 play essential roles in chondrocyte differentiation and, thereby, in cartilage formation. Their discovery will help to understand further the molecular mechanisms controlling chondrogenesis in vivo, uncover genetic mechanisms underlying cartilage diseases, and develop novel strategies for cartilage repair.

Sox18 Is Transiently Expressed during Angiogenesis in Granulation Tissue of Skin Wounds with an Identical Expression Pattern to Flk-1 mRNA

Sox18 encodes a member of the Sry-related high mobility group box (SOX) family of developmental transcription factors. Examination of Sox18 expression during embryogenesis has shown that Sox18 is expressed transiently in endothelial cells of developing blood vessels, and mutations in Sox18 have been found to underlie the mouse vascular and hair follicle mutant ragged. In this study we have examined the expression of Sox18 in angiogenesis during wound healing. Full-thickness skin wounds were created in mice, and subsequent expression of vascular endothelial growth factor (VEGF), the VEGF receptor Flk-1, α1 (iv) collagen (Col4a1), and Sox18 were studied using in situ hybridization. As has been previously reported, VEGF was expressed predominantly in the keratinocytes at the wound margins. Sox18 expression was found five days after wounding during capillary sprouting in granulation tissue and persisted through the proliferative phase of healing, but was not detected in fully epithelialized wounds 21 days after wounding. Sox18 mRNA expression was detected in capillaries within the granulation tissue and showed an identical pattern of distribution to Flk-1 and Col4a1 mRNA expression in endothelial cells. Immunostaining with a polyclonal anti-Sox18 antibody showed SOX18 protein localized in capillary endothelial cells within the granulation tissue. Capillaries in the subcutaneous tissue of unwounded skin showed no Sox18 expression. Sox18 may therefore represent a transcription factor involved in the induction of angiogenesis during wound healing and tissue repair, but not in the maintenance of endothelial cells in undamaged tissue.

Sox9 induces testis development in XX transgenic mice.

Mutations in SOX9 are associated with male-to-female sex reversal in humans. To analyze Sox9 function during sex determination, we ectopically expressed this gene in XX gonads. Here, we show that Sox9 is sufficient to induce testis formation in mice, indicating that it can substitute for the sex-determining gene Sry.

The SOX10 transcription factor: evaluation as a candidate gene for central and peripheral hereditary myelin disorders.

The SOX10 transcription factor is involved in development of neural crest derivatives and fate determination in glial cells. SOX10 mutations have been found in patients with intestinal aganglionosis and depigmentation with deafness (Waardenburg-Hirschsprung). Associated neurological signs have been reported in some cases, including a patient exhibiting a central and peripheral myelin deficiency. Therefore, we screened for SOX10 mutations in a large cohort of patients with peripheral and central myelin disorders. 56 were affected by classical demyelinating Charcot-Marie-Tooth disease without identified mutations in the genes encoding PNS myelin proteins (PMP22, P0), connexin 32 and the zinc-finger transcription factor, EGR2. 88 patients with undetermined leukodystrophy were selected from a large European prospective study. Associated clinical, magnetic resonance imaging and electrophysiological signs were consistent with a defect in CNS myelination in 83 and with an active degeneration of the CNS myelin in 5. No abnormalities in the proteolipid protein gene (PLP) were found. The absence of SOX100 mutation in this large cohort of patients suggests that this gene is not frequently involved in peripheral or central inherited myelin disorders.

Cloning and functional analysis of the Sry-related HMG box gene, Sox18

The Sox gene family (Sry like HMG box gene) is characterised by a conserved DNA sequence encoding a domain of approximately 80 amino acids which is responsible for sequence specific DNA binding. We initially published the identification and partial cDNA sequence of murine Sox18, a new member of this gene family, isolated from a cardiac cDNA library. This sequence allowed us to classify Sox18 into the F sub-group of Sox proteins, along with Sox7 and Sox17. Recently, we demonstrated that mutations in the Sox18 activation domain underlie cardiovascular and hair follicle defects in the mouse mutation, ragged (Ra) (Pennisi et al., 2000. Mutations in Sox18 underlie cardiovascular and hair follicle defecs in ragged mice. Nat. Genet. 24, 434–437). Ra homozygotes lack vibrissae and coat hairs, have generalised oedema and an accumulation of chyle in the peritoneum. Here we have investigated the genomic sequences encoding Sox18. Screening of a mouse genomic phage library identified four overlapping clones, we sequenced a 3.25 kb XbaI fragment that defined the entire coding region and approximately 1.5 kb of 5′ flanking sequences. This identified (i) an additional 91 amino acids upstream of the previously designated methionine start codon in the original cDNA, and (ii) an intron encoded within the HMG box/DNA binding domain in exactly the same position as that found in the Sox5, -13 and -17 genes. The Sox18 gene encodes a protein of 468 aa. We present evidence that suggests HAF-2, the human HMG-box activating factor -2 protein, is the orthologue of murine Sox18. HAF-2 has been implicated in the regulation of the Human IgH enhancer in a B cell context. Random mutagenesis coupled with GAL4 hybrid analysis in the activation domain between amino acids 252 and 346, of Sox18, implicated the phosphorylation motif, SARS, and the region between amino acid residues 313 and 346 as critical components of Sox18 mediated transactivation. Finally, we examined the expression of Sox18 in multiple adult mouse tissues using RT-PCR. Low-moderate expression was observed in spleen, stomach, kidney, intestine, skeletal muscle and heart. Very abundant expression was detected in lung tissue.

Genetic study of SOX9 in a case of campomelic dysplasia.

Campomelic dysplasia (CD) is a sporadic autosomal dominant syndrome that results in skeletal malformation and developmental abnormalities. Death usually occurs neonatally as a result of respiratory insufficiencies, but life expectancy varies depending on the severity of the phenotype. XY sex reversal is common in CD, and a range of genital defects is observed in males and females. CD is due to mutations in SOX9, a member of the SOX (SRY-related HMG box) gene family. SOX9 is a transcription factor involved in chondrogenesis and sex determination. We present a CD patient with a normal 46,XX karyotype and female phenotype. Single-stranded conformation polymorphism analysis of DNA from this CD patient demonstrated a single-stranded conformation polymorphism shift in the C-terminal region of SOX9. DNA sequencing showed a frameshift mutation resulting from the insertion of a single guanine residue in nucleotide region 1,453-1,456. This insertion mutation creates a mutant SOX9 open reading frame that is 201 nucleotides longer than the normal gene. It has been shown that the C-terminal region of SOX9 is responsible for the transactivating ability of the protein. The frameshift identified here affects approximately half of the protein region needed for full transactivating function. We hypothesize that residual SOX9 function may explain why this patient survived infancy.

Sry, Sox9 and mammalian sex determination.

Sry is the Y-chromosomal gene that acts as a trigger for male development in mammalian embryos. This gene encodes a high mobility group (HMG) box transcription factor that is known to bind to specific target sequences in DNA and to cause a bend in the chromatin. DNA bending appears to be part of the mechanism by which Sry influences transcription of genes downstream in a cascade of gene regulation leading to maleness, but the factors that cooperate with, and the direct targets of, Sry remain to be identified. One gene known to be downstream from Sry in this cascade in Sox9, which encodes a transcription factor related to Sry by the HMG box. Like Sry, mutations in Sox9 disrupt male development, but unlike Sry, the role of Sox9 is not limited to mammals. This review focuses on what is known about the two genes and their likely modes of action, and draws together recent data relating to how they might interconnect with the network of gene activity implicated in testis determination in mammals.