Two new members of the murine Sim gene family are transcriptional repressors and show different expression patterns during mouse embryogenesis.
From a cDNA library of mouse skeletal muscle, we have isolated mouse Sim1 (mSim1) cDNA encoding a polypeptide of 765 amino acids with striking amino acid identify in basic helix-loop-helix (89% identify) and PAS (89 % identify) domains to previously identified mSim2, although the carboxy-terminal third of the molecule did not show any similarity to mSim2 or Drosophila Sim (dSim). Yeast two-hybrid analysis and coimmunoprecipitation experiments demonstrated that both of the mSim gene products interacted with Arnt even more efficiently than AhR, a natural partner of Arnt, suggesting a functional cooperativity with Arnt. In sharp contrast with dSim having transcriptional-enhancing activity in the carboxy-terminal region, the two mSims possessed a repressive activity toward Arnt in the heterodimer complex. This is the first example of bHLH-PAS proteins with transrepressor activity, although some genetic data suggest that dSim plays a repressive role in gene expression (Z. Chang, D. Price, S. Bockheim, M. J. Boedigheimer, R. Smith, and A. Laughon, Dev. Biol. 160:315-322, 1993; D. M. Mellerick and M. Nirenberg, Dev. Biol. 171:306-316, 1995). Whole-mount in situ hybridization showed restricted and characteristic expression patterns of the two mSim mRNAs in various tissues and organs during embryogenesis, such as those for the somite, the nephrogenic cord, and the mesencephalon (for mSim1) and those for the diencephalon, branchial arches, and limbs (for mSim2). From sequence similarity and chromosomal localization, it is concluded that mSim2 is an ortholog of hSim2, which is proposed to be a candidate gene responsible for Down's syndrome. The sites of mSim2 expression showed an overlap with the affected regions of the syndrome, further strengthening involvement of mSim2 in Down's syndrome.
Ema
M
M
Department of Chemistry, Graduate School of Science, Tohoku University, Sendai, Japan.
Morita
M
M
Ikawa
S
S
Tanaka
M
M
Matsuda
Y
Y
Gotoh
O
O
Saijoh
Y
Y
Fujii
H
H
Hamada
H
H
Kikuchi
Y
Y
Fujii-Kuriyama
Y
Y
D000595:Amino Acid Sequence; D000818:Animals; D051792:Basic Helix-Loop-Helix Proteins; D001921:Brain / Q000196:embryology / Q000378:metabolism; D019556:COS Cells; D002460:Cell Line; D002874:Chromosome Mapping; D003001:Cloning, Molecular; D004268:DNA-Binding Proteins / Q000737:chemistry; D004330:Drosophila; D029721:Drosophila Proteins; D005314:Embryonic and Fetal Development; D018507:Gene Expression Regulation, Developmental; D015723:Gene Library; D018257:Helix-Loop-Helix Motifs; D006801:Humans; D017404:In Situ Hybridization, Fluorescence; D007621:Karyotyping; D051379:Mice; D008969:Molecular Sequence Data; D005810:Multigene Family; D018482:Muscle, Skeletal / Q000196:embryology / Q000378:metabolism*; D009687:Nuclear Proteins / Q000737:chemistry; D015347:RNA Probes; D011993:Recombinant Fusion Proteins / Q000096:biosynthesis / Q000737:chemistry; D011994:Recombinant Proteins / Q000096:biosynthesis; D012097:Repressor Proteins / Q000096:biosynthesis* / Q000737:chemistry; D017386:Sequence Homology, Amino Acid
D051792:Basic Helix-Loop-Helix Proteins; D004268:DNA-Binding Proteins; D029721:Drosophila Proteins; D009687:Nuclear Proteins; D015347:RNA Probes; D011993:Recombinant Fusion Proteins; D011994:Recombinant Proteins; D012097:Repressor Proteins; C491094:SIM1 protein, human; C101750:Sim1 protein, mouse; C089449:sim protein, Drosophila