title: Pontin and Reptin regulate cell proliferation in early Xenopus embryos in collaboration with c-Myc and Miz-1.
abstract: Pontin (Tip49) and Reptin (Tip48) are highly conserved components of multimeric protein complexes important for chromatin remodelling and transcription. They interact with many different proteins including TATA box binding protein (TBP), beta-catenin and c-Myc and thus, potentially modulate different pathways. As antagonistic regulators of Wnt-signalling, they control wing development in Drosophila and heart growth in zebrafish. Here we show that the Xenopus xPontin and xReptin in conjunction with c-Myc regulate cell proliferation in early development. Overexpression of xPontin or xReptin results in increased mitoses and bending of embryos, which is mimicked by c-Myc overexpression. Furthermore, the knockdown of either xPontin or xReptin resulted in embryonic lethality at late gastrula stage, which is abrogated by the injection of c-Myc-RNA. The N-termini of xPontin and xReptin, which mediate the mitogenic effect were mapped to contain c-Myc interaction domains. c-Myc protein promotes cell cycle progression either by transcriptional activation through the c-Myc/Max complex or by repression of cyclin dependent kinase inhibitors (p21, p15) through c-Myc/Miz-1 interaction. Importantly, xPontin and xReptin exert their mitogenic effect through the c-Myc/Miz-1 pathway as dominant negative Miz-1 and wild-type c-Myc but not a c-Myc mutant deficient in Miz-1 binding could rescue embryonic lethality. Finally, promoter reporter studies revealed that xPontin and xReptin but not the N-terminal deletion mutants enhance p21 repression by c-Myc. We conclude that xPontin and xReptin are essential genes regulating cell proliferation in early Xenopus embryogenesis through interaction with c-Myc. We propose a novel function of xPontin and xReptin as co-repressors in the c-Myc/Miz-1 pathway.
authors.affiliation: Zoologisches Institut II, Universität Karlsruhe (TH), Kaiserstrasse 12, 76131 Karlsruhe, Germany.
authors.forename: Christelle
authors.initials: C
authors.lastname: Etard
authors.forename: Dietmar
authors.initials: D
authors.lastname: Gradl
authors.forename: Martin
authors.initials: M
authors.lastname: Kunz
authors.forename: Martin
authors.initials: M
authors.lastname: Eilers
authors.forename: Doris
authors.initials: D
authors.lastname: Wedlich
mesh_terms: D000074183:ATPases Associated with Diverse Cellular Activities; D000818:Animals; D015415:Biomarkers; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism*; D049109:Cell Proliferation; D004265:DNA Helicases / Q000235:genetics / Q000378:metabolism*; D004625:Embryo, Nonmammalian / Q000166:cytology* / Q000196:embryology / Q000378:metabolism*; D018507:Gene Expression Regulation, Developmental; D009154:Mutation / Q000235:genetics; D011485:Protein Binding; D016271:Proto-Oncogene Proteins c-myc / Q000235:genetics / Q000378:metabolism*; D013997:Time Factors; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*; D029867:Xenopus Proteins / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D014982:Xenopus laevis / Q000196:embryology* / Q000235:genetics / Q000378:metabolism
chemical_list: D015415:Biomarkers; D002352:Carrier Proteins; D016271:Proto-Oncogene Proteins c-myc; D014157:Transcription Factors; D029867:Xenopus Proteins; D000074183:ATPases Associated with Diverse Cellular Activities; D004265:DNA Helicases; C486548:Ruvbl1 protein, Xenopus; C486547:RUVBL2 protein, Xenopus