SALL1 Mutations Research Articles

WNT pathways and upper limb anomalies

The various Wnt pathways that are related to upper limb anomalies are reviewed. Abnormalities in the Wnt7a pathway (located in the dorsal ectoderm) produce several clinically relevant conditions such as the palmar duplication syndrome, nail patella syndrome, ulnar ray deficiency, limb hypoplasia, polysyndactyly and the palmar nail syndrome. Abnormalities of the Wnt3/3a pathway (located in the apical ectodermal ridge) include tetra-amelia and loss of the distal phalanges/nails. Abnormalities of the Wnt5/5a pathway (located in the apical ectodermal ridge as well as in the mesoderm) will affect chondrogenesis of the developing limb and experimental Wnt5a(-/-) limbs have terminal adactyly. Chondrogenesis and limb muscle differentiation are both affected by several Wnt pathways and these will be reviewed in details. Abnormalities in LRP 5/6 (a co-receptor for Wnts) lead to congenital bone disease and Wnt4 is specifically involved in joint development. Finally, the relationship between the Wnt pathway and SALL4 (mutations of which cause Okihiro/Duane-radial ray deficiency in humans) are discussed.

Phenotypic variability in a family with Townes–Brocks syndrome

Townes-Brocks syndrome (TBS) is an autosomal dominant disorder characterized by external ear anomalies with sensorineural hearing loss, limb anomalies, renal and anorectal malformations. TBS is caused by mutations in SALL1, a gene mapped to chromosome 16q12.1. We report three generations of a family with SALL1 c.1326delC (p.Ser442fs) mutation, showing increased clinical severity over generations. The members of the first generation demonstrated polydactyly and deafness. In the second generation, the mother and uncle of the proband additionally had renal and/or anal anomalies. The proband in the third generation showed the most severe symptoms including congenital heart disease. Increase in clinical severity in successive generations in TBS cannot be explained genetically. There is wide clinical variation in TBS; however, most affected parents are usually mildly affected and may have similarly or more severely affected children. Social and/or physical bias at reproduction may contribute to an apparent increase in clinical severity over generations in TBS.

A mouse line expressing Sall1‐driven inducible Cre recombinase in the kidney mesenchyme

Sall1 is expressed in the metanephric mesenchyme in the developing kidney, and mice deficient in Sall1 show kidney agenesis or dysgenesis. Sall1 is also expressed elsewhere, including in the limb buds, anus, heart, and central nervous system. Dominant-negative mutations of Sall1 in mice and humans lead to developmental defects in these organs. Here, we generated a mouse line expressing tamoxifen-inducible Cre recombinase (CreER(T2)) under the control of the endogenous Sall1 promoter. Upon tamoxifen treatment, these mice showed genomic recombination in the tissues where endogenous Sall1 is expressed. When CreER(T2) mice were crossed with the floxed Sall1 allele, tamoxifen administration during gestation led to a significant decrease in Sall1 expression and small kidneys at birth, suggesting that Sall1 functions were disrupted. Furthermore, Sall1 expression in the kidney was significantly reduced by neonatal tamoxifen treatment. The Sall1CreER(T2) mouse is a valuable tool for in vivo time-dependent and region-specific knockout and overexpression studies.

CHN1 mutations are not a common cause of sporadic Duane's retraction syndrome

<i>CHN1</i> mutations are not a common cause of sporadic Duane's retraction syndrome

Familial transmission of oculoauriculovertebral spectrum (Goldenhar syndrome) is not due to mutations in either EYA1 or SALL1

Familial transmission of oculoauriculovertebral spectrum (Goldenhar syndrome) is not due to mutations in either EYA1 or SALL1

Nephropathy in Townes-Brocks syndrome (SALL1 mutation): imaging and pathological findings in adulthood

Townes-Brocks syndrome (TBS) is a rare autosomal dominant disease, resulting from mutation in the developmental gene SALL1. The phenotype encompasses malformations of limbs (triphalangeal thumbs and pre-axial polydactyly), intestine (anal stenosis) and ears (dysplastic ear with perception hearing loss). Renal involvement (hypo-dysplasia, multicystic kidneys or unilateral absence) is observed in almost half of patients and may progress to end-stage renal failure in childhood. Herein, we report two adult patients diagnosed with TBS at age 28 and 35. Both exhibited severe chronic renal failure and kidney hypodysplasia by imaging studies while focal and segmental glomerulosclerosis (FSGS) was demonstrated in one case. Regular assessment of glomerular filtration rate is mandatory throughout life in all TBS patients.

Sall1, Sall2, and Sall4 Are Required for Neural Tube Closure in Mice

Four homologs to the Drosophila homeotic gene spalt (sal) exist in both humans and mice (SALL1 to SALL4/Sall1 to Sall4, respectively). Mutations in both SALL1 and SALL4 result in the autosomal-dominant developmental disorders Townes-Brocks and Okihiro syndrome, respectively. In contrast, no human diseases have been associated with SALL2 to date, and Sall2-deficient mice have shown no apparent abnormal phenotype. We generated mice deficient in Sall2 and, contrary to previous reports, 11% of our Sall2-deficient mice showed background-specific neural tube defects, suggesting that Sall2 has a role in neurogenesis. To investigate whether Sall4 may compensate for the absence of Sall2, we generated compound Sall2 knockout/Sall4 genetrap mutant mice. In these mutants, the incidence of neural tube defects was significantly increased. Furthermore, we found a similar phenotype in compound Sall1/4 mutant mice, and in vitro studies showed that SALL1, SALL2, and SALL4 all co-localized in the nucleus. We therefore suggest a fundamental and redundant function of the Sall proteins in murine neurulation, with the heterozygous loss of a particular SALL protein also possibly compensated in humans during development.

SALL1 truncated protein expression in Townes-Brocks syndrome leads to ectopic expression of downstream genes

Mutations in SALL1 lead to the dominant multiorgan congenital anomalies that define Townes-Brocks syndrome (TBS). The majority of these mutations result in premature termination codons that would be predicted to trigger nonsense-mediated decay (NMD) of mutant mRNA and cause haploinsufficiency. Our previous studies using a gene targeted mouse model (Sall1-DeltaZn) suggested that TBS phenotypes are due to expression of a truncated mutant protein, not haploinsufficiency. In this report, we strengthen this hypothesis by showing that expression of the mutant protein alone in transgenic mice is sufficient to cause limb phenotypes that are characteristic of TBS patients. We prove that the same pathogenetic mechanism elucidated in mice is occurring in humans by demonstrating that truncated SALL1 protein is expressed in cells derived from a TBS patient. TBS mutant protein is capable of dominant negative activity that results in ectopic activation of two downstream genes, Nppa and Shox2, in the developing heart and limb. We propose a model for the pathogenesis of TBS in which truncated Sall1 protein causes derepression of Sall-responsive target genes.

Sall genes regulates limb patterning through modulation of region‐specific Hox activities in mice

Sall genes encode zinc finger transcription factors, and Sall1 and Sall4 are causative genes for human syndromes, such as Towns‐Brocks syndrome and Okihiro syndromes, respectively. Patients with these syndromes show multiple defects including those in limbs. In order to understand the molecular mechanisms by which Sall genes control limb development, we have analyzed mice with targeted mutations in Sall1 and Sall3. While a single knockout of Sall1 and Sall3 shows subtle defects, double mutants exhibited severe defects in autopod development. We found that Sall1 interacts with Hoxa13 and Hoxd13, important genes controlling proper development of the autopod. Further analyses suggest that the coordinated action of Sall and Hox regulates target gene expression and patterning of the autopod. Our study provides molecular insights into how region‐specific morphogenesis is regulated in the autopod.Supported by NIH (5 R01 HD034538‐10) and Grant‐in‐aid by the Ministry of Education, Culture, Sports, Science, and Technology, Japan.

Two coding single nucleotide polymorphisms in the SALL1 gene in Townes-Brocks syndrome: a case report and review of the literature

Townes-Brocks syndrome (TBS) is an autosomal dominantly inherited malformation syndrome characterized by imperforate anus and limb and ear malformations with sensorineural hearing loss. Mutations in SALL1, a gene mapping to chromosome 16q21.1, are responsible for TBS. Here, we described a 16-month-old male patient with typical TBS clinical features including imperforate anus and preaxial polydactyly. Two coding polymorphism sites were identified in this case. One is silent (rs1965024, 2574 C > T), whereas the other yields a new codon encoding a different amino acid (rs4614723, 3823 G > A). The hot spot mutations in exon 2 were not suggested. Therefore, lack of SALL1 gene mutations and the presence of variable phenotypes in the sporadic cases might suggest DNA alternations in the noncoding regions of SALL1 gene and/or in other genes modulating SALL1 gene expression or functions.

The Association of an Epibulbar Dermoid and Duane Syndrome in a Patient with a SALL1 Mutation (Townes-Brocks Syndrome)

Introduction: Townes-Brocks Syndrome (TBS) is an autosomal dominant condition characterized by renal, anal, ear and thumb anomalies caused by SALL1 mutations. Ocular manifestations reported have included congenital cataracts, unilateral microphthalmia, optic nerve atrophy, and unilateral visual loss with bilateral Brushfield Spots. Iris and chorioretinal colobomata were described in one individual whose daughter had Duane syndrome. Methods: We present a case of TBS with a proven SALL1 mutation associated with unique ophthalmic features. Case Report: The first child of healthy unrelated parents was born after an uncomplicated pregnancy with multiple features consistent with TBS. The patient was heterozygous for a pathogenic SALL1 gene mutation c826C > T (pR276X). The child had an epibulbar dermoid and left Type 1 Duane syndrome. He also had tearing when he ate food (crocodile tears). Discussion: This case adds to the current knowledge of ophthalmic associations with SALL1 mutations; features characteristic of SALL1 mutations and others more commonly associated with SALL4 mutations (2) (epibulbar dermoid and Duane) being present. Truncated SALL1 protein alters the localization of full length SALL4 providing a theoretical mechanism for these associations, alternatively SALL1 mutations cause associated eye problems more directly. The possibility of chance association cannot be excluded. Our case is only the second we have found with a SALL1 mutation and TBS with Duane syndrome and the first to also have an epibulbar dermoid. The mutation present is that most commonly associated with TBS. Conclusion: This case increases the demand to examine all children TBS for ophthalmic abnormalities.

Nonsense‐mediated decay and the molecular pathogenesis of mutations in SALL1 and GLI3

Mutations in SALL1 and GLI3 are responsible for human limb malformation syndromes. The molecular pathophysiology of these mutations is incompletely understood, and many conclusions have been drawn from studies performed in the mouse. We identified truncating mutations in SALL1 and GLI3 in patients with limb malformation and studied the contribution of nonsense-mediated decay (NMD) to the expression of mutant mRNA in patient-derived fibroblasts. Quantification of the relative proportions of mutant and wild-type alleles was performed by pyrosequencing. In SALL1, a mutant allele causing Townes-Brocks syndrome was unexpectedly resistant to NMD, whereas a different mutation causing a much milder phenotype was susceptible to NMD. In GLI3, all three mutant alleles tested were susceptible to NMD. This work provides novel insights into the molecular pathophysiology of SALL1 and GLI3 mutations, extends the phenotypic spectrum of SALL1 mutations, and provides an example of a human mutation which does not follow the usual accepted positional rules governing mammalian NMD. (c) 2007 Wiley-Liss, Inc.

Wide phenotypic variations within a family with SALL1 mutations: Isolated external ear abnormalities to Goldenhar syndrome

We report on wide phenotypic variations within a family with SALL1 mutations; the elder sister presented with a Townes-Brocks syndrome phenotype including external ear anomalies, preaxial polydactyly, and anteriorly placed anus, whereas the younger sister presented with a phenotype resembling Goldenhar syndrome, including atretic ear canals, mandibular hypoplasia, and right preaxial polydactyly as well as an epibulbar dermoid. The mother had abnormal external ears but was otherwise structurally normal, and the father was asymptomatic. Analysis of the SALL1 gene revealed that both daughters were heterozygous for nonsense mutation 1256T>A (L419X), that is present 5' to the region encoding the first double zinc finger. The mother was heterozygous for the L419X mutation. The younger daughter is the first patient with a SALL1 mutation to exhibit a classic Goldenhar syndrome-like phenotype with an epibulbar dermoid. The observation lends further support to the concept that Goldenhar syndrome is an etiologically heterogeneous disorder that may have a genetic basis in some cases.

Synergistic cooperation of Sall4 and Cyclin D1 in transcriptional repression

Loss of function mutations in SALL4 cause Okihiro syndrome, an autosomal dominant disorder characterised by radial ray malformations associated with Duane anomaly. In zebrafish and mouse Sall4 interacts with TBX5 during limb and heart development and plays a crucial role for embryonic stem (ES) cell pluripotency. Here we report the nuclear interaction of murine Sall4 with Cyclin D1, one of the main regulators of G 1 to S phase transition in cell cycle, verified by yeast two-hybrid assay, co-immunoprecipitation and intracellular co-localisation. Furthermore, using luciferase reporter gene assays we demonstrate that Sall4 operates as a transcriptional repressor located to heterochromatin and that this activity is modulated by Cyclin D1.

Localization of a Gene for Nonsyndromic Renal Hypodysplasia to Chromosome 1p32-33

Nonsyndromic defects in the urinary tract are the most common cause of end-stage renal failure in children and account for a significant proportion of adult nephropathy. The genetic basis of these disorders is not fully understood. We studied seven multiplex kindreds ascertained via an index case with a nonsyndromic solitary kidney or renal hypodysplasia. Systematic ultrasonographic screening revealed that many family members harbor malformations, such as solitary kidneys, hypodysplasia, or ureteric abnormalities (in a total of 29 affected individuals). A genomewide scan identified significant linkage to a 6.9-Mb segment on chromosome 1p32-33 under an autosomal dominant model with reduced penetrance (peak LOD score 3.5 at D1S2652 in the largest kindred). Altogether, three of the seven families showed positive LOD scores at this interval, demonstrating heterogeneity of the trait (peak HLOD 3.9, with 45% of families linked). The chromosome 1p32-33 interval contains 52 transcription units, and at least 23 of these are expressed at stage E12.5 in the murine ureteric bud and/or metanephric mesenchyme. These data show that autosomal dominant nonsyndromic renal hypodysplasia and associated urinary tract malformations are genetically heterogeneous and identify a locus for this common cause of human kidney failure.

Mouse homolog of SALL1, a causative gene for Townes–Brocks syndrome, binds to A/T‐rich sequences in pericentric heterochromatin via its C‐terminal zinc finger domains

The Spalt (sal) gene family is conserved from Drosophila to humans. Mutations of human SALL1 cause Townes-Brocks syndrome, with features of ear, limb, anal, renal and heart anomalies. Sall1, a murine homolog of SALL1, is essential for kidney formation, and both Sall1 and SALL1 localize to heterochromatin in the nucleus. Here, we present a molecular mechanism for the heterochromatin localization of Sall1. Mutation analyses revealed that the 7th-10th C-terminal double zinc finger motifs were required for the localization. A recombinant protein of the most C-terminal double zinc finger (9th-10th) bound to specific A/T-rich sequences. Furthermore, Sall1 associated with A/T-rich sequences of the major satellite DNA in heterochromatin. Thus Sall1 may bind to A/T-rich sequences of the major satellite DNA via its C-terminal double zinc fingers, thereby mediating its localization to heterochromatin.

Townes-Brocks syndrome: twenty novelSALL1 mutations in sporadic and familial cases and refinement of theSALL1 hot spot region

Townes-Brocks syndrome (TBS) is an autosomal dominant malformation syndrome characterized by renal, anal, ear, and thumb anomalies caused by SALL1 mutations. To date, 36 SALL1 mutations have been described in TBS patients. All but three of those, namely p.R276X, p.S372X, and c.1404dupG, have been found only in single families thereby preventing phenotype-genotype correlations. Here we present 20 novel mutations (12 short deletions, five short duplications, three nonsense mutations) in 20 unrelated families. We delineate the phenotypes and report previously unknown ocular manifestations, i.e. congenital cataracts with unilateral microphthalmia. We show that 46 out of the now 56 SALL1 mutations are located between the coding regions for the glutamine-rich domain mediating SALL protein interactions and 65 bp 3' of the coding region for the first double zinc finger domain, narrowing the SALL1 mutational hotspot region to a stretch of 802 bp within exon 2. Of note, only two SALL1 mutations would result in truncated proteins without the glutamine-rich domain, one of which is reported here. The latter is associated with anal, ear, hand, and renal manifestations, indicating that the glutamine-rich domain is not required for typical TBS.

SALL1 mutations in sporadic Townes–Brocks syndrome are of predominantly paternal origin without obvious paternal age effect

Autosomal dominant Townes-Brocks syndrome (TBS) is characterized by imperforate anus, triphalangeal and supernumerary thumbs, dysplastic ears and sensorineural hearing loss, and may also involve other organ systems. Strong inter- and intrafamiliar variability is known. Approximately 50% of TBS cases are sporadic and due to de novo mutations in the SALL1 gene. SALL1 encodes a zinc finger protein operating as a transcriptional repressor and localizing to pericentromeric heterochromatin. We traced the parental origin of SALL1 mutations in sporadic TBS by analysis of linkage between SALL1 mutations and exonic or intronic polymorphisms in 16 families with 10 different mutations. Mutations were of paternal origin in 14 of 16 cases (87.5%). Paternal origin was independent of the mutation type. The mean paternal age at conception was 29.9 and the mean maternal age 26.5 years. We conclude that de novo mutations in SALL1 mostly occur on the paternally derived chromosome 16 without an obvious age effect.

A Conserved 12-Amino Acid Motif in Sall1 Recruits the Nucleosome Remodeling and Deacetylase Corepressor Complex

Sall1 is a multi-zinc finger transcription factor that represses gene expression and regulates organogenesis. In this report, we further characterize the domain of Sall1 necessary for repression. We show that endogenous Sall1 binds to the nucleosome remodeling and deacetylase corepressor complex (NuRD) and confirm the functionality of the Sall1-associating macromolecular complex by showing that the complex possesses HDAC activity. NuRD is involved in global transcriptional repression and regulation of specific developmental processes. The mechanism by which sequence-specific DNA-binding proteins associate with NuRD is not well understood. We have identified a highly conserved 12-amino acid motif in the transcription factor Sall1 that is sufficient for the recruitment of NuRD. Single amino acid substitutions defined the critical amino acid peptide motif as RRKQXK-PXXF. This motif probably exhibits a more general role in regulating gene expression, since other proteins containing this domain, including all Sall family members and an unrelated zinc finger protein Ebfaz, mediate transcriptional repression and associate with NuRD. These results also have important implications for the pathogenesis of Townes-Brocks, a syndrome caused by SALL1 mutations.

The murine homolog ofSALL4, a causative gene in Okihiro syndrome, is essential for embryonic stem cell proliferation, and cooperates withSall1in anorectal, heart, brain and kidney development

Mutations in SALL4, the human homolog of the Drosophila homeotic gene spalt (sal), cause the autosomal dominant disorder known as Okihiro syndrome. In this study, we show that a targeted null mutation in the mouse Sall4 gene leads to lethality during peri-implantation. Growth of the inner cell mass from the knockout blastocysts was reduced, and Sall4-null embryonic stem (ES) cells proliferated poorly with no aberrant differentiation. Furthermore, we demonstrated that anorectal and heart anomalies in Okihiro syndrome are caused by Sall4 haploinsufficiency and that Sall4/Sall1 heterozygotes exhibited an increased incidence of anorectal and heart anomalies, exencephaly and kidney agenesis. Sall4 and Sall1 formed heterodimers, and a truncated Sall1 caused mislocalization of Sall4 in the heterochromatin; thus, some symptoms of Townes-Brocks syndrome caused by SALL1 truncations could result from SALL4 inhibition.