The Drosophila homeodomain transcription factor, Vnd, associates with a variety of cofactors, is extensively phosphorylated, and forms multiple complexes in embryos

• Published in: The FEBS journal 2008-09, Vol.275 (20), p.5062-5073
• Main Authors: Zhang, Huanqing, Syu, Li-Jyun, Modica, Vicky, Yu, Zhongxin, Von Ohlen, Tonia, Mellerick, Dervla M.
• Format: Article
• Language: English
• ISSN: 1742-464X; 1742-4658
• DOI: 10.1111/j.1742-4658.2008.06639.x

Vnd is a dual transcriptional regulator that is essential for Drosophil a 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 to embryonic Vnd, which forms multiple high molecular weight complexes. Unlike its vertebrate homologue, Nkx2.2, full length Vnd can bind its target in EMSA, suggesting that co-factor availability may influence Vnd's weak regulatory activity in transient transfections. We identify the HMG1-type protein, D1, and the novel HLH 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 we show that Vnd is extensively phosphorylated in embryos and that it can be phosphorylated by activated MAP kinase in vitro . These results highlight the complexities of Vnd-mediated regulation.