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  • Title: The mammalian single-minded (SIM) gene: mouse cDNA structure and diencephalic expression indicate a candidate gene for Down syndrome.
    Author: Yamaki A, Noda S, Kudoh J, Shindoh N, Maeda H, Minoshima S, Kawasaki K, Shimizu Y, Shimizu N.
    Journal: Genomics; 1996 Jul 01; 35(1):136-43. PubMed ID: 8661114.
    Abstract:
    We have recently isolated a human homolog (hSIM) of the Drosophila single-minded (sim) gene from the Down syndrome critical region of chromosome 21 using the exon trapping method. The Drosophila sim gene encodes a transcription factor that regulates the development of the central nervous system midline cell lineage. To elucidate the structure of the mammalian SIM protein, we have isolated cDNA clones from a mouse embryo cDNA library. The cDNA clones encode a polypeptide of 657 amino acids with a bHLH (basic-helix-loop-helix) domain, characteristic of a large family of transcription factors, and a PAS (Per-Arnt-Sim) domain in the amino-terminal half region. Both of these domains have striking sequence homology with human SIM and Drosophila SIM proteins. In contrast, the carboxy-terminal half of the mouse SIM protein consists of a proline-rich region with no sequence homology to the Drosophila SIM protein. A similar proline-rich domain is known for the activator domain of a number of transcription factors. Whole-mount embryo in situ hybridization experiments revealed that the SIM mRNA is expressed prominently in the diencephalon of mouse embryos at 8-9.5 days postcoitum. The structural characteristics of the mouse SIM protein and its expression in the diencephalon during embryogenesis strongly suggest that the newly isolated mammalian SIM homolog may play a critical role in the development of the mammalian central nervous system. We propose that the human SIM gene may be one of the pathogenic genes of Down syndrome.
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