title: The Drosophila homeodomain transcription factor, Vnd, associates with a variety of co-factors, is extensively phosphorylated and forms multiple complexes in embryos.
abstract: Vnd is a dual transcriptional regulator that is essential for Drosophila dorsal-ventral patterning. Yet, our understanding of the biochemical basis for its regulatory activity is limited. Consistent with Vnd's ability to repress target expression in embryos, endogenously expressed Vnd physically associates with the co-repressor, Groucho, in Drosophila Kc167 cells. Vnd exists as a single complex in Kc167 cells, in contrast with embryonic Vnd, which forms multiple high-molecular-weight complexes. Unlike its vertebrate homolog, Nkx2.2, full-length Vnd can bind its target in electrophoretic mobility shift assay, suggesting that co-factor availability may influence Vnd's weak regulatory activity in transient transfections. We identify the high mobility group 1-type protein, D1, and the novel helix-loop-helix protein, Olig, as novel Vnd-interacting proteins using co-immunoprecipitation assays. Furthermore, we demonstrate that both D1 and Olig are co-expressed with Vnd during Drosophila embryogenesis, consistent with a biological basis for this interaction. We also suggest that the phosphorylation state of Vnd influences its ability to interact with co-factors, because Vnd is extensively phosphorylated in embryos and can be phosphorylated by activated mitogen-activated protein kinase in vitro. These results highlight the complexities of Vnd-mediated regulation.
authors.affiliation: MSRBIII, Ann Arbor, MI, USA.
authors.forename: Huanqing
authors.initials: H
authors.lastname: Zhang
authors.forename: Li-Jyun
authors.initials: LJ
authors.lastname: Syu
authors.forename: Vicky
authors.initials: V
authors.lastname: Modica
authors.forename: Zhongxin
authors.initials: Z
authors.lastname: Yu
authors.forename: Tonia
authors.initials: T
authors.lastname: Von Ohlen
authors.forename: Dervla M
authors.initials: DM
authors.lastname: Mellerick
mesh_terms: D000818:Animals; D051792:Basic Helix-Loop-Helix Proteins / Q000378:metabolism*; D002460:Cell Line; D004268:DNA-Binding Proteins / Q000378:metabolism*; D004330:Drosophila; D029721:Drosophila Proteins / Q000378:metabolism*; D004625:Embryo, Nonmammalian; D018398:Homeodomain Proteins / Q000378:metabolism*; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D010766:Phosphorylation; D011485:Protein Binding; D012097:Repressor Proteins / Q000378:metabolism; D014157:Transcription Factors / Q000378:metabolism*
chemical_list: D051792:Basic Helix-Loop-Helix Proteins; D004268:DNA-Binding Proteins; D029721:Drosophila Proteins; D018398:Homeodomain Proteins; D020928:Mitogen-Activated Protein Kinases; D012097:Repressor Proteins; D014157:Transcription Factors; C046995:D1 protein, Drosophila; C091023:gro protein, Drosophila; C094797:vnd protein, Drosophila
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