Drosophila sine oculis and eyes absent genes synergize in compound-eye formation. The murine homologues of these genes, Six and Eya, respectively, show overlapping expression patterns during development. We hypothesized that Six and Eya proteins cooperate to regulate their target genes. Cotransfection assays were performed with various combinations of Six and Eya to assess their effects on a potential natural target, myogenin promoter, and on a synthetic promoter, the thymidine kinase gene promoter fused to multimerized Six4 binding sites. A clear synergistic activation of these promoters was observed in certain combinations of Six and Eya. To investigate the molecular basis for the cooperation, we first examined the intracellular distribution of Six and Eya proteins in transfected COS7 cells. Coexpression of Six2, Six4, or Six5 induced nuclear translocation of Eya1, Eya2, and Eya3, which were otherwise distributed in the cytoplasm. In contrast, coexpression of Six3 did not result in nuclear localization of any Eya proteins. Six and Eya proteins were coimmunoprecipitated from nuclear extracts prepared from cotransfected COS7 cells and from rat liver. Six domain and homeodomain, two evolutionarily conserved domains among various Six proteins, were necessary and sufficient for the nuclear translocation of Eya. In contrast, the Eya domain, a conserved domain among Eya proteins, was not sufficient for the translocation. A specific interaction between the Six domain and homeodomain of Six4 and Eya2 was observed by yeast two-hybrid analysis. Our results suggest that transcription regulation of certain target genes by Six proteins requires cooperative interaction with Eya proteins: complex formation through direct interaction and nuclear translocation of Eya proteins. This implies that the synergistic action of Six and Eya is conserved in the mouse and is mediated through cooperative activation of their target genes.Six genes are mouse homologues of the Drosophila sine oculis (so) gene, which is essential for compound-eye formation (9, 31). Six members of the Six family of genes have so far been identified in the mouse (17,18,27,28,35). Each Six gene shows a specific expression pattern during development of the mouse embryo. Six1 and Six2 show expression in mesenchymal cells around E8.5 to E10.5 and in muscles and limb tendons in later stages (28). Six3 is expressed in the rostral forebrain in earlier stages and is confined to the prospective eye region (27). Six4 proteins are distributed in the peripheral region of the mantle layer of the developing brain and spinal cord and in various ganglia between E9.5 and E14.5 (25). Six5 mRNA is expressed as early as E7 and is abundantly expressed in neonatal heart and skeletal muscles (24). Human SIX5 resides downstream of a CTG repeat, whose expansion leads to myotonic dystrophy (DM) (7). Since SIX5 is expressed in several tissues affected by DM and the transcription of SIX5 is repressed by the causative a CTG repeat expansion, it has been proposed that SIX5 is involved in som...

Drosophila sine oculis, eyes absent, and dachshund are essential for compound eye formation and form a gene network with direct protein interaction and genetic regulation. The vertebrate homologues of these genes, Six, Eya, and Dach, also form a similar genetic network during muscle formation. To elucidate the molecular mechanism underlying the network among Six, Eya, and Dach, we examined the molecular interactions among the encoded proteins. Eya interacted directly with Six but never with Dach. Dach transactivated a multimerized GAL4 reporter gene by coproduction of GAL4-Eya fusion proteins. Transactivation by Eya and Dach was repressed by overexpression of VP16 or E1A but not by E1A mutation, which is defective for CREB binding protein (

The cDNA clones encoding ARE(Na,K-ATPase alpha1 subunit gene regulatory element) binding protein AREC3 were isolated from myoblast C2C12 cells and mouse skeletal muscle cDNA library. At least four alternatively spliced forms of AREC3 cDNA were identified. Sequence analysis indicates that AREC3 has an extensive homology with the Drosophila sine oculis gene product required for development of the entire visual system [Cheyette et al.(1994) Neuron 12, 977-996]. The homologous region including a homeodomain is required for specific DNA binding to ARE. A transactivation domain was identified in the C-terminal part of the AREC3 by reporter gene assays using GAL4-AREC3 fusion protein constructs. Immunohistochemistry revealed that AREC3 localized to the nucleus and cytoplasm of myoblast C2C12 cells, and the production of AREC3 is augmented during muscle differentiation. Western blot analysis indicated that the 115 kDa form of AREC3 protein is increased in the cytoplasmic extract, and the 67kDa form is increased both in nuclear and cytoplasmic extracts of C2C12 cells during muscle differentiation.

We identified five cDNA clones of the Six gene family which are expressed in retina. They are Six2, Six3ct and Six3[~ (which are derived from alternative splicing forms), Six5, and AREC3/Six4. All of these Six family genes possess extensive sequence similarity among each other in the so-homologous region (Six domain and homeodomain) but differ greatly in structure in some other regions. The amino acid sequence similarity of the so-homologous region to the previously identified AREC31Six4 is 70.1% for Six2, 57.3% for Six3ct and Six3[~, and 70.3% for Six5. The expression of these genes was observed in inner and outer nuclear layer, ganglion cell layer, and pigment epithelium of mouse retina by in situ hybridization. The so-homologous region of each Six family protein has specific DNA binding activity. Six5 and Six2 bind to the same sequence as does AREC31Six4, while Six3 does not. These observations suggest that some of the Six family genes can regulate the same target genes.cloned. The roles of these Six family genes in retina formation are discussed. Materials and methods Screening of the cDNA library and DNA sequencingThe mouse retina eDNA library from 1-month-old BALB/c mice was kindly supplied by Dr. Ananda Swaroop [7]. A SalI-DraI (-17 2486) fragment of AREC3 eDNA (pSVSPORTMI8) [3] was labeled with [32P]dCTP with a Megaprime labeling kit (Amersham). About 1.2x 10 6 plaques were screened and we obtained 13 positive clones. They were grouped into 4 based on restriction mapping and partial nucleotide sequencing. The overlapping clones were sequenced and we obtained four species of Six family cDNAs. The nucleotide sequence data reported in this paper will appear in the DDBJ, EMBL and GenBank nucleotide sequence databases with the following accession numbers: D83147 (Six2), D83144 (Six3cq, D83145 (Six313) and D83146 (Six5).

We analyzed the expression of mouse DMAHP / Six5 (the myotonic dystrophy-associated homeodomain protein gene) during embryogenesis and in various tissues by northern blotting. Expression was observed as early as embryonic day 7 (E7) and continued to E17. Abundant expression was observed in neonatal heart and skeletal muscle with potential links to the phenotype of myotonic dystrophy. The transcription initiation sites of the gene were analyzed in mouse E11 and E15 embryos and in adult skeletal and heart muscle. Three major transcription initiation sites were identified, the proximal site was specific to the early E11 embryo, while the other two were common among the heart and skeletal muscle and E11 and E15 embryos. All transcription initiation sites were downstream of the corresponding CTG repeat locus of the mouse gene (-1195), excluding a possible inclusion of the CUG repeat sequence in mRNA leading to abnormal splicing or to translation of aberrant protein. For analysis of the regulatory elements in the promoter region, we used P19 embryonal carcinoma cells which abundantly express mouse DMAHP / Six5. Multiple positive and negative elements were identified in the promoter region. All positive elements were Sp1/Sp3 binding sites and one of the negative elements was a novel factor binding site. The transcription initiation sites and regulatory elements are conserved between human and mouse DMAHP.