Role of SOX10 in the Development of Neural Crest-Derived Melanocytes and Glia
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Oncogene (2003) 22, 3024–3034 & 2003 Nature Publishing Group All rights reserved 0950-9232/03 $25.00 www.nature.com/onc The importance of having your SOX on: role of SOX10 in the development of neural crest-derived melanocytes and glia Ramin Mollaaghababa1 and William J Pavan*,1 1National Human Genome Research Institute, National Institutes of Health, 49 Convent Drive, Bethesda, MD 20892-4472, USA SOX10w is a member of the high-mobility group-domain differentiate to form melanocytes of the skin, hair, and SOX family of transcription factors, which are ubiqui- inner ear while others move ventrally, either through the tously found in the animal kingdom. Disruption of neural somites or in the space between the somites and the crest development in the Dominant megacolon (Dom) neural tube, and contribute to the formation of mice is associated with a Sox10 mutation. Mutations in additional distinct lineage. These include sensory human Sox10 w gene have also been linked with the neurons and glia, neurons and glia of cranial ganglia, occurrence of neurocristopathies in the Waardenburg– cartilage and bone, connective tissue, and neuroendo- Shah syndrome type IV (WS-IV), for which the Sox10Dom crine cells (Le Douarin and Kalcheim, 1999). mice serve as a murine model. The neural crest disorders The specification of neural crest to distinct lineage in the Sox10Dom mice and WS-IV patients consist of and their proper differentiation is dependent on both hypopigmentation, cochlear neurosensory deafness, and intrinsic factors and environmental interactions (La- enteric aganglionosis. Consistent with these observations, Bonne and Bronner-Fraser, 1998). The use of mouse a critical role for SOX10 in the proper differentiation of neural crest mutants has been instrumental in the neural crest-derived melanocytes and glia has been identification and analysis of genes essential for proper demonstrated. Emerging data also show an important neural crest function (Le Douarin and Kalcheim, 1999). role for SOX10 in promoting the survival of neural crest In particular, the critical role of a number of transcrip- precursor cells prior to lineage commitment. Several genes tion factors in differentiation and function of neural whose regulation is dependent on SOX10 function have crest cell (NCC) lineage was established using mouse been identified in the peripheral nervous system and in mutants. This review article focuses on one such melanocytes, helping to begin the identification of the transcription factor called SOX10 (acronym for Sry-like multiple pathways that appear to be modulated by SOX10 HMG bOX), which has a significant function in proper activity. In this review, we will discuss the biological development of the NCCs. We will present a synthesis of relevance of these target genes to neural crest development the current state of knowledge about SOX10 and its and the properties of Sox10 as a transcription factor. developmental role, discussing the implications of these Oncogene (2003) 22, 3024–3034. doi:10.1038/sj.onc.1206442 findings and their relevance to future work. Keywords: SOX10w; neural crest; glia; melanocytes; differentiation; transcription factor Discovery of SOX10 Sox10 was first discovered by RT–PCR analysis of total Introduction RNA from 11.5-day-old mouse embryos (E11.5), using degenerate oligonucleotide primers directed against the The health and survival of all organisms depends on high-mobility group (HMG) domain (Wright et al., proper differentiation and function of diverse cell types. 1993). Members of the HMG-domain family are DNA- During vertebrate development, a variety of distinct cell binding proteins that fall into a vast array of functional types are derived from a special precursor population categories (Bianchi and Beltrame, 2000). Their HMG called the neural crest (Le Douarin and Kalcheim, 1999; Knecht and Bronner-Fraser, 2002). Neural crest cells designation relates to the observation that the family members initially analysed showed fast migration on originate dorsally at the top, or ‘crest’, of the neural tube SDS–PAGE. Sequence comparison showed that within in early development, and travel in well-defined migra- the HMG group, SOX10 belongs to the SOX family of tory paths following epithelial-to-mesenchymal conver- proteins, which are related to the mammalian testis sion and detachment from the neural tube (Erickson and determination factor SRY (Gubbay et al., 1990). More Reedy, 1998). Some follow a dorso-lateral pathway and than 20 vertebrate SOX members have been identified to date, and related genes have been found in Drosophila *Correspondence: WJ Pavan; E-mail: [email protected] melanogaster and Caenorhabditis elegans (Wright et al., wGene symbols and proteins are respectively designated by italic and 1993; Pevny and Lovell-Badge, 1997; Wegner, 1999). upper-case letters throughout the text. SOX proteins show restricted patterns of tissue-specific SOX10 function in neural crest development R Mollaaghababa and WJ Pavan 3025 expression and are essential for a multitude of develop- (HSCR) (Shah et al., 1981; Badner and Chakravarti, mental processes, including nervous system develop- 1990; Parisi and Kapur, 2000). These include cochlear ment, bone morphogenesis, pigment cell formation, deafness and pigmentary defects (heterochromia iridis, formation of the germ layer, development of the white forelock and eyelashes, leukoderma) characteristic immune system, sex determination, and eye develop- of the Waardenburg disorder, and enteric aganglionosis ment (for reviews, refer to Pevny and Lovell-Badge, in the distal region of colon characteristic of the HSCR. 1997; Wegner, 1999). Based on pairwise comparisons of The illustration of the genetic defect in the Dom mice led partial HMG-domain sequences, the SOX members to the identification of Sox10 mutations in a number of were originally classified into six separate groups (A–E), individuals with WS-IV features (Pingault et al., 1998; with SOX8, SOX9, and SOX10 belonging to group E Bondurand et al., 1999; Inoue et al., 1999; Southard- (Wright et al., 1993). This was later expanded to seven Smith et al., 1999b; Touraine et al., 2000; Sham et al., (van de Wetering and Clevers, 1993; Meyer et al., 1996) 2001a). A Sox10 mutation (795delG) that does not give and eight groups (A–H) (Osaki et al., 1999), owing to the established features of WS-IV but presents with the discovery of additional SOX genes. The latest phenotypes associated with abnormal neural crest refinements of these classifications are based on full- development has also been identified in an individual length protein sequences comparisons. They consist of (Pingault et al., 2000). A list of these mutations, along the addition of two new groups, I and J, in a study that with those identified in mice and zebrafish, is presented included the invertebrate SOX sequences (Bowles et al., in Figure 2. They include frameshift mutations, inser- 2000), and subdivision of group B into B1 and B2 tions, deletions, extensions, and point mutations, and (Uchikawa et al., 1999; Bowles et al., 2000; Kamachi span different domains of the SOX10 protein. However, et al., 2000). Since its discovery in mouse, Sox10 no mutations within the regulatory region of Sox10 have homologues have been identified in several other been linked to neurocristopathy phenotypes to date. vertebrates. In rat, the Sox10 gene was cloned from Identification of such mutations in the future should rat glial cells (Kulhbrodt et al., 1998a). Human Sox10 help with discovery of transactivating factors that was identified by characterization of a cosmid from a modulate Sox10 expression. human chromosome-22-specific library and by com- parative mapping studies (Pusch et al., 1998; Southard- Smith et al., 1999a). Molecular analysis of the zebrafish SOX10 structure mutation colourless (cls) led to the discovery of a Sox10 et al homologue in this organism (Dutton ., 2001). In HMG domain chick, a Sox10 homologue was identified by screening of a chick embryo cDNA library with HMG-domain- A better appreciation of the functional properties of specific degenerate primers (Cheng et al., 2000). A SOX10 requires an understanding of the structural Sox10-related homologue has also been identified in the mechanisms by which SOX10 binds its target DNA and invertebrate species D. melanogaster. The Drosophila regulates transcription. Similar to other HMG proteins, homologue (Sox100B) was discovered by sequence SOX10 binds its target DNA sequences via its HMG homology within the HMG domain and is equally domain (Figure 2), and mutations in the HMG box related to the Sox9 gene (Loh and Russell, 2000). Its disrupt SOX10 structure and compromise its binding to function in the fruit fly remains to be elucidated. A DNA (Southard-Smith et al., 1999b; Bondurand et al., sequence comparison of SOX10 across these different 2000). Model structures of the SOX10 HMG domain species is presented in Figure 1. This alignment shows have been generated from human, rat, and mouse the high degree of sequence conservation for SOX10 sequences by threading each sequence through the during evolution, underscoring its functional signifi- NMR coordinates of the second HMG-1 box from cance and suggesting that many of the mechanisms rat, followed by energy minimization studies to deter- governing neural crest development may be conserved mine the most favorable conformation (Southard-Smith throughout vertebrate evolution. et al., 1999b). The predicted structure is composed of three alpha-helices forming an L shape, which is proposed to facilitate binding to the DNA. The HMG box is highly conserved within the SOX family, with Identification of Sox10 mutation in Waardenburg–Shah X90% amino-acid sequence identity within an indivi- type IV mouse model dual SOX group and about 60% identity between distant groups (Kamachi et al., 2000). Interest in the functional role of SOX10 intensified with The evolutionary conserved HMG motif consists of the discovery that the neurocristopathy phenotypes in about 80 amino acids and binds in the minor groove of the Dominant megacolon (Dom) mice are linked to a DNA (Weiss, 2001). In addition to conferring DNA- Sox10 mutation (Herbarth et al.