SALL1, the gene mutated in Townes-Brocks syndrome, encodes a transcriptional repressor which interacts with TRF1/PIN2 and localizes to pericentromeric heterochromatin.

Institute of Human Genetics, University of Göttingen, Heinrich-Düker-Weg 12, 37073 Göttingen, Germany.
Human Molecular Genetics (Impact Factor: 7.69). 01/2002; 10(26):3017-24. DOI: 10.1093/hmg/10.26.3017
Source: PubMed

ABSTRACT The Townes-Brocks syndrome (TBS) is an autosomal dominantly inherited malformation syndrome presenting as an association of imperforate anus, triphalangeal and supernumerary thumbs, malformed ears and sensorineural hearing loss. Mutations in SALL1, a gene mapping to 16q12.1, were identified as a cause for TBS. To elucidate how SALL1 mutations lead to TBS, we have performed a series of functional studies with the SALL1 protein. Using epifluorescence and confocal microscopy it could be shown that a GFP-SALL1 fusion protein localizes to chromocenters and smaller heterochromatin foci in transiently transfected NIH-3T3 cells. Chromocenters consist of clustered pericentromeric heterochromatin and contain telomere sequences. Indirect immunofluorescence revealed a partial colocalization of GFP-SALL1 with M31, the mouse homolog of the Drosophila heterochromatic protein HP1. It was further demonstrated that SALL1 acts as a strong transcriptional repressor in mammalian cells. Transcriptional repression could not be relieved by the addition of the histone deacetylase inhibitor Trichostatin-A. In a yeast two-hybrid screen we identified PIN2, an isoform of telomere-repeat-binding factor 1 (TRF1), as an interaction partner of SALL1, and showed that the N-terminus of SALL1 is not necessary for the interaction with PIN2/TRF1. The interaction was confirmed in vitro in a GST-pulldown assay. The association of the developmental regulator SALL1 with heterochromatin is striking and unexpected. Our results propose an involvement of SALL1 in the regulation of higher order chromatin structures and indicate that the protein might be a component of a distinct heterochromatin-dependent silencing process. We have also provided new evidence that there is a close functional link between the centromeric and telomeric heterochromatin domains not only in Drosophila and yeast, but also in mammalian cells.

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    ABSTRACT: The SALL4 gene, Drosophila's region specific homeotic sal (spalt)-like gene family member, encodes for a zinc finger (ZF) transcription factor (TF). Mutations of the SALL4 have been demonstrated to cause the Okihiro syndrome a combination of Duane retraction syndrome and radial ray defects. We have studied a missense point mutation of the SALL4 (nucleotide substitution 2663A→G, residues substitution His:888→Arg:888) positioned within the first c2h2 ZF of the C-terminal double ZF motif in the SALL4 gene identified in an Italian three-generation family, some members of which displayed the clinical features of the Okihiro syndrome. We performed a molecular modeling study on the wild type ( wt ) and mutated ( mt ) ZF domains of the SALL4 TF with the goal to propose a plausible hypothesis relating the modeled structural and energetic differences between the wt and mt forms to the defects connected with the observed mutation. Sequence alignment, homology protein modeling and molecular mechanics using CFF91 force field were utilized to build and refine the ZF models and to estimate their stability and DNA-binding affinity. We have modeled wt and mt ZF motifs of the SALL4 TF based on sequence homology with ZF domains of TFs with known crystal structures co-crystallized with a B-DNA segment. Secondary structure, zinc ion binding and DNA binding of the two static ZF models were analyzed in terms of mutual r.m.s. deviations and intramolecular and intermolecular interaction energies. The modeled wt and mt forms of ZF motif of the SALL4 TF did not display significant structural differences cased by steric strain or charge of the bulkier Arg:888 and retained similar supersecondary structures and comparable strength of the zinc ion binding. However, more significant differences were predicted in their binding affinities to DNA. Calculated higher DNA binding affinity (and possibly also changed specificity) of the mt form of the ZF could be the reason for the altered activator/repressor function of the mutant form of the SALL4 TF at its natural target gene or the cause for erroneous targeting of a different DNA sequence of the same or another gene. We may thus hypothesize that the pathogenic effects of the mutation could be related to the altered regulation function by making the dissociation of the mt SALL4 TF-gene adducts more difficult.
    Internet Electronic Journal of Molecular Design. 01/2004;
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    ABSTRACT: Members of the spalt (sal) gene family encode zinc-finger proteins that are putative tumor suppressors and regulate anteroposterior (AP) patterning, cellular identity, and, possibly, cell cycle progression. The mechanism through which sal genes carry out these functions is unclear. The Caenorhabditis elegans sal gene sem-4 controls the fate of several different cell types, including neurons, muscle and hypodermis. Mutation of sem-4 transforms particular tail neurons into touch-neuron-like cells. In wild-type C. elegans, six touch receptor neurons mediate the response of the worm to gentle touch. All six touch neurons normally express the LIM homeobox gene mec-3. A subset, the two PLM cells, also express the Hox gene egl-5, an Abdominal-B homolog, which we find is required for correct mec-3 expression in these cells. The abnormal touch-neuron-like-cells in sem-4 animals express mec-3; we show that a subset also express egl-5. We report: (1) that ectopic expression of sem-4 in normal touch cells represses mec-3 expression and reduces touch cell function; (2) that egl-5 expression is required for both the fate of normal PLM touch neurons in wild-type animals and the fate of a subset of abnormal touch neurons in sem-4 animals, and (3) that SEM-4 specifically binds a shared motif in the mec-3 and egl-5 promoters that mediates repression of these genes in cells in the tail. We conclude that sem-4 represses egl-5 and mec-3 through direct interaction with regulatory sequences in the promoters of these genes, that sem-4 indirectly modulates mec-3 expression through its repression of egl-5 and that this negative regulation is required for proper determination of neuronal fates. We suggest that the mechanism and targets of regulation by sem-4 are conserved throughout the sal gene family: other sal genes might regulate patterning and cellular identity through direct repression of Hox selector genes and effector genes.
    Development 09/2003; 130(16):3831-40. · 6.21 Impact Factor
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    ABSTRACT: The SALL (Spalt-like) family of zinc-finger transcription factors is conserved in metazoans. In Drosophila Sal (Spalt) and Salr (Spalt-related) control the expression of genes involved in wing and central nervous system development, including cell adhesion and cytoskeletal proteins. In humans, SALL mutations associate with congenital disorders such as the Townes-Brocks and Okihiro syndromes. Human and Drosophila SALL proteins are modified by SUMO (small ubiquitin-related modifier), which influences their subnuclear localization. In the present study, we have analysed the transcriptional activity of Drosophila Sall proteins in cultured cells. We show that both Sal and Salr act as transcriptional repressors in Drosophila cells where they repress transcription through an AT-rich sequence. Furthermore, using the UAS/Gal4 heterologous system, Drosophila Sal and Salr repress transcription in human cells. Under our experimental conditions, only in the case of Salr is the repression activity dependent on the HDAC (histone deacetylase) complex. This complex might interact with the C-terminal zinc fingers of Salr. We describe the differential subcellular localizations of Sal and Salr fragments and identify their repression domains. Surprisingly, both repressors also contain transcription activation domains. In addition, under our experimental conditions SUMOylation has differential effects on Sal and Salr repressor activity. Phylogenetic comparison between nematodes, insects and vertebrates identifies conserved peptide sequences that are presumably critical for SALL protein function.
    Biochemical Journal 06/2011; 438(3):437-45. · 4.65 Impact Factor