Early Mammalian Development Laboratory, John Curtin School of Medical Research, The Australian National University, Canberra, ACT 2601, Australia.
Early Development, MRC Harwell Institute, Harwell Campus, Oxfordshire OX11 0RD, UK.
J Cell Sci. 2021 May 1;134(9). doi: 10.1242/jcs.256792. Epub 2021 May 17.
Zinc finger of the cerebellum (Zic) proteins act as classic transcription factors to promote transcription of the Foxd3 gene during neural crest cell specification. Additionally, they can act as co-factors that bind proteins from the T-cell factor/lymphoid enhancing factor (TCF/LEF) family (TCFs) to repress WNT-β-catenin-dependent transcription without contacting DNA. Here, we show that ZIC activity at the neural plate border is influenced by WNT-dependent SUMOylation. In the presence of high canonical WNT activity, a lysine residue within the highly conserved zinc finger N-terminally conserved (ZF-NC) domain of ZIC5 is SUMOylated, which reduces formation of the ZIC-TCF co-repressor complex and shifts the balance towards transcription factor function. The modification is crucial in vivo, as a ZIC5 SUMO-incompetent mouse strain exhibits neural crest specification defects. This work reveals the function of the ZF-NC domain within ZIC, provides in vivo validation of target protein SUMOylation and demonstrates that WNT-β-catenin signalling directs transcription at non-TCF DNA-binding sites. Furthermore, it can explain how WNT signals convert a broad region of Zic ectodermal expression into a restricted region of neural crest cell specification.
小脑锌指（Zic）蛋白作为经典的转录因子，在神经嵴细胞特化过程中促进 Foxd3 基因的转录。此外，它们还可以作为共因子，与 T 细胞因子/淋巴增强因子（TCF/LEF）家族（TCFs）的蛋白结合，抑制 WNT-β-catenin 依赖性转录，而不与 DNA 接触。在这里，我们表明，神经板边界的 ZIC 活性受 WNT 依赖性 SUMO 化的影响。在高经典 WNT 活性存在的情况下，ZIC5 的高度保守锌指 N 端保守（ZF-NC）结构域内的一个赖氨酸残基被 SUMO 化，这减少了 ZIC-TCF 共抑制复合物的形成，并将平衡转向转录因子功能。该修饰在体内至关重要，因为 ZIC5 的 SUMO 失活小鼠品系表现出神经嵴特化缺陷。这项工作揭示了 ZIC 中 ZF-NC 结构域的功能，为靶蛋白 SUMO 化提供了体内验证，并证明了 WNT-β-catenin 信号在非 TCF DNA 结合位点指导转录。此外，它可以解释 WNT 信号如何将 Zic 外胚层表达的广泛区域转化为神经嵴细胞特化的受限区域。
