SIAM_XENLA
ID SIAM_XENLA Reviewed; 246 AA.
AC Q91848;
DT 06-FEB-2007, integrated into UniProtKB/Swiss-Prot.
DT 01-NOV-1996, sequence version 1.
DT 03-AUG-2022, entry version 99.
DE RecName: Full=Homeobox protein siamois;
GN Name=siamois {ECO:0000303|PubMed:9371792};
OS Xenopus laevis (African clawed frog).
OC Eukaryota; Metazoa; Chordata; Craniata; Vertebrata; Euteleostomi; Amphibia;
OC Batrachia; Anura; Pipoidea; Pipidae; Xenopodinae; Xenopus; Xenopus.
OX NCBI_TaxID=8355;
RN [1] {ECO:0000305, ECO:0000312|EMBL:CAA88495.1}
RP NUCLEOTIDE SEQUENCE [MRNA], FUNCTION, TISSUE SPECIFICITY, AND DEVELOPMENTAL
RP STAGE.
RC TISSUE=Gastrula {ECO:0000269|PubMed:7720076};
RX PubMed=7720076; DOI=10.1016/0092-8674(95)90373-9;
RA Lemaire P., Garrett N., Gurdon J.B.;
RT "Expression cloning of siamois, a novel Xenopus homeobox gene expressed in
RT dorsal-vegetal cells of blastulae and capable of inducing a complete
RT secondary axis.";
RL Cell 81:85-94(1995).
RN [2] {ECO:0000305}
RP FUNCTION, AND INDUCTION.
RX PubMed=8898219; DOI=10.1242/dev.122.10.3055;
RA Carnac G., Kodjabachian L., Gurdon J.B., Lemaire P.;
RT "The homeobox gene Siamois is a target of the Wnt dorsalisation pathway and
RT triggers organiser activity in the absence of mesoderm.";
RL Development 122:3055-3065(1996).
RN [3] {ECO:0000305}
RP INDUCTION.
RX PubMed=8948596; DOI=10.1006/dbio.1996.0306;
RA Brannon M., Kimelman D.;
RT "Activation of Siamois by the Wnt pathway.";
RL Dev. Biol. 180:344-347(1996).
RN [4] {ECO:0000305}
RP FUNCTION, AND INDUCTION.
RX PubMed=9308964; DOI=10.1101/gad.11.18.2359;
RA Brannon M., Gomperts M., Sumoy L., Moon R.T., Kimelman D.;
RT "A beta-catenin/XTcf-3 complex binds to the siamois promoter to regulate
RT dorsal axis specification in Xenopus.";
RL Genes Dev. 11:2359-2370(1997).
RN [5] {ECO:0000305}
RP FUNCTION, AND MUTAGENESIS OF GLN-191.
RX PubMed=9217000; DOI=10.1242/dev.124.13.2581;
RA Fan M.J., Sokol S.Y.;
RT "A role for Siamois in Spemann organizer formation.";
RL Development 124:2581-2589(1997).
RN [6] {ECO:0000305}
RP FUNCTION, AND MUTAGENESIS OF GLN-191.
RX PubMed=9371792; DOI=10.1073/pnas.94.24.13017;
RA Kessler D.S.;
RT "Siamois is required for formation of Spemann's organizer.";
RL Proc. Natl. Acad. Sci. U.S.A. 94:13017-13022(1997).
RN [7] {ECO:0000305}
RP INDUCTION.
RX PubMed=9917834; DOI=10.1111/j.1749-6632.1998.tb10109.x;
RA Nelson R.W., Gumbiner B.M.;
RT "Beta-catenin directly induces expression of the Siamois gene, and can
RT initiate signaling indirectly via a membrane-tethered form.";
RL Ann. N. Y. Acad. Sci. 857:86-98(1998).
RN [8] {ECO:0000305}
RP INDUCTION.
RX PubMed=9576934; DOI=10.1073/pnas.95.10.5626;
RA Fan M.J., Gruning W., Walz G., Sokol S.Y.;
RT "Wnt signaling and transcriptional control of Siamois in Xenopus embryos.";
RL Proc. Natl. Acad. Sci. U.S.A. 95:5626-5631(1998).
RN [9] {ECO:0000305}
RP FUNCTION.
RX PubMed=11291853;
RA Engleka M.J., Kessler D.S.;
RT "Siamois cooperates with TGFbeta signals to induce the complete function of
RT the Spemann-Mangold organizer.";
RL Int. J. Dev. Biol. 45:241-250(2001).
RN [10] {ECO:0000305}
RP FUNCTION.
RX PubMed=11578862; DOI=10.1016/s0925-4773(01)00484-1;
RA Kodjabachian L., Lemaire P.;
RT "Siamois functions in the early blastula to induce Spemann's organiser.";
RL Mech. Dev. 108:71-79(2001).
RN [11] {ECO:0000305}
RP FUNCTION.
RX PubMed=12710967; DOI=10.1016/s0012-1606(03)00034-4;
RA Yamamoto S., Hikasa H., Ono H., Taira M.;
RT "Molecular link in the sequential induction of the Spemann organizer:
RT direct activation of the cerberus gene by Xlim-1, Xotx2, Mix.1, and
RT Siamois, immediately downstream from Nodal and Wnt signaling.";
RL Dev. Biol. 257:190-204(2003).
RN [12] {ECO:0000305}
RP FUNCTION.
RX PubMed=15923623; DOI=10.1128/mcb.25.12.5061-5072.2005;
RA Snider L., Tapscott S.J.;
RT "XIC is required for Siamois activity and dorsoanterior development.";
RL Mol. Cell. Biol. 25:5061-5072(2005).
CC -!- FUNCTION: Essential for Wnt/beta-catenin-mediated formation of the
CC Spemann organizer and for induction of the organizer precursor, the
CC Nieuwkoop center. Acts as a transcriptional activator, cooperating with
CC TGFbeta signals to induce a program of organizer-specific gene
CC expression and to generate an organizer with both head- and trunk-
CC inducing activity. Activates the head organizer gene cer1 by acting
CC synergistically with otx2 and mix-A/mix.1 through the 5'-TAATCT-3'
CC element of the cer1 promoter. Also binds as a complex with lhx1/lim1
CC and mix-A/mix.1 to the 3x 5'-TAAT-3' element of the cer1 promoter.
CC Required for subsequent dorsoventral axis formation in the embryo,
CC dorsalizing ventral mesoderm and cooperating with t/bra to induce
CC dorsal mesoderm. Also involved in neural induction, inducing the cement
CC gland and neural tissue in overlying ectoderm. Later in development,
CC has the second function of indirectly repressing ventral genes,
CC probably by activating the expression of a transcriptional repressor.
CC {ECO:0000269|PubMed:11291853, ECO:0000269|PubMed:11578862,
CC ECO:0000269|PubMed:12710967, ECO:0000269|PubMed:15923623,
CC ECO:0000269|PubMed:7720076, ECO:0000269|PubMed:8898219,
CC ECO:0000269|PubMed:9217000, ECO:0000269|PubMed:9308964,
CC ECO:0000269|PubMed:9371792}.
CC -!- SUBCELLULAR LOCATION: Nucleus {ECO:0000305}.
CC -!- TISSUE SPECIFICITY: Most abundant in dorsal-vegetal cells of late
CC blastulae/early gastrulae embryos. {ECO:0000269|PubMed:7720076}.
CC -!- DEVELOPMENTAL STAGE: Not expressed maternally. Expression begins
CC shortly after the midblastula transition, peaks at the early gastrula
CC stage and is still detectable until the tailbud stage. Accumulation
CC during the blastula stage precedes that of the organizer genes gsc,
CC lhx1/lim-1, and t/bra. {ECO:0000269|PubMed:7720076}.
CC -!- INDUCTION: By wnt-signaling and by the dorsalizing factor LiCl.
CC Activated in the dorsal side of the embryo by a ctnnb1-tcf7l1 (beta
CC catenin-tcf3) complex. Repressed on the ventral side by tcf7l1/tcf3
CC alone. Autoregulated by siamois itself. {ECO:0000269|PubMed:8898219,
CC ECO:0000269|PubMed:8948596, ECO:0000269|PubMed:9308964,
CC ECO:0000269|PubMed:9576934, ECO:0000269|PubMed:9917834}.
CC -!- MISCELLANEOUS: Named 'siamois' (French for siamese) because ectopic
CC expression leads to the formation of embryos with duplicated axial and
CC head structures, which resemble siamese twins.
CC {ECO:0000269|PubMed:7720076}.
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DR EMBL; Z48606; CAA88495.1; -; mRNA.
DR PIR; A56219; A56219.
DR RefSeq; NP_001079305.1; NM_001085836.1.
DR AlphaFoldDB; Q91848; -.
DR SMR; Q91848; -.
DR GeneID; 378613; -.
DR KEGG; xla:378613; -.
DR CTD; 378613; -.
DR Xenbase; XB-GENE-864865; sia1.L.
DR OrthoDB; 1014909at2759; -.
DR Proteomes; UP000186698; Chromosome 3L.
DR Bgee; 378613; Expressed in gastrula and 1 other tissue.
DR GO; GO:0005634; C:nucleus; IC:UniProtKB.
DR GO; GO:0005667; C:transcription regulator complex; IDA:UniProtKB.
DR GO; GO:0043565; F:sequence-specific DNA binding; IDA:UniProtKB.
DR GO; GO:0030154; P:cell differentiation; IEA:UniProtKB-KW.
DR GO; GO:0001707; P:mesoderm formation; IGI:UniProtKB.
DR GO; GO:0007399; P:nervous system development; IEA:UniProtKB-KW.
DR GO; GO:0045944; P:positive regulation of transcription by RNA polymerase II; IMP:UniProtKB.
DR GO; GO:0045893; P:positive regulation of transcription, DNA-templated; IDA:UniProtKB.
DR GO; GO:0060062; P:Spemann organizer formation at the dorsal lip of the blastopore; IMP:UniProtKB.
DR GO; GO:0016055; P:Wnt signaling pathway; IGI:UniProtKB.
DR CDD; cd00086; homeodomain; 1.
DR InterPro; IPR009057; Homeobox-like_sf.
DR InterPro; IPR001356; Homeobox_dom.
DR Pfam; PF00046; Homeodomain; 1.
DR SMART; SM00389; HOX; 1.
DR SUPFAM; SSF46689; SSF46689; 1.
DR PROSITE; PS50071; HOMEOBOX_2; 1.
PE 1: Evidence at protein level;
KW Activator; Developmental protein; Differentiation; DNA-binding;
KW Gastrulation; Homeobox; Neurogenesis; Nucleus; Reference proteome;
KW Transcription; Transcription regulation; Wnt signaling pathway.
FT CHAIN 1..246
FT /note="Homeobox protein siamois"
FT /id="PRO_0000274549"
FT DNA_BIND 142..201
FT /note="Homeobox"
FT /evidence="ECO:0000255|PROSITE-ProRule:PRU00108"
FT REGION 84..107
FT /note="Disordered"
FT /evidence="ECO:0000256|SAM:MobiDB-lite"
FT REGION 199..246
FT /note="Disordered"
FT /evidence="ECO:0000256|SAM:MobiDB-lite"
FT COMPBIAS 205..219
FT /note="Polar residues"
FT /evidence="ECO:0000256|SAM:MobiDB-lite"
FT SITE 191
FT /note="Determines DNA-binding specificity"
FT /evidence="ECO:0000269|PubMed:9217000,
FT ECO:0000269|PubMed:9371792"
FT MUTAGEN 191
FT /note="Q->E: Abolishes dorsoventral patterning."
FT /evidence="ECO:0000269|PubMed:9217000,
FT ECO:0000269|PubMed:9371792"
FT MUTAGEN 191
FT /note="Q->K: Disrupts dorsoventral patterning."
FT /evidence="ECO:0000269|PubMed:9217000,
FT ECO:0000269|PubMed:9371792"
SQ SEQUENCE 246 AA; 28451 MW; EF35DAD86ED74755 CRC64;
MTYEAEMEQI VSTALTLQDD YIKFTPRNQN MACHAEIIGI FHDIHPTVEI KEPHQDKSVL
QETLVELYSV LGIPQEPQVS KTMKFEEPEQ HKESSSTVTR SDSLVNSLQS TGLKRPFCED
EHREYKKPLI QAEDISPATS TRSRKRTIYS KEQTNFLQNQ FDLNPYPDFV NRCRIAKITG
IPEPRIQVWF QNRRARHLPR ATTFHSPQGR KSPTSEGPRS FLSREAHYPD EWGQAPNPSN
TQPYPN
