Division of Molecular Cardiovascular Biology, Cincinnati Children’s Hospital Medical Center, University of Cincinnati College of Medicine, Cincinnati, OH 45229, USA.
Hum Mol Genet. 2012 Apr 15;21(8):1888-96. doi: 10.1093/hmg/dds002. Epub 2012 Jan 10.
Limb anomalies are important birth defects that are incompletely understood genetically and mechanistically. GLI3, a mediator of hedgehog signaling, is a genetic cause of limb malformations including pre- and postaxial polydactyly, Pallister-Hall syndrome and Greig cephalopolysyndactyly. A closely related Gli (glioma-associated oncogene homolog)-superfamily member, ZIC3, causes X-linked heterotaxy syndrome in humans but has not been investigated in limb development. During limb development, post-translational processing of Gli3 from activator to repressor antagonizes and posteriorly restricts Sonic hedgehog (Shh). We demonstrate that Zic3 and Gli3 expression overlap in developing limbs and that Zic3 converts Gli3 from repressor to activator in vitro. In Gli3 mutant mice, Zic3 loss of function abrogates ectopic Shh expression in anterior limb buds, limits overexpression in the zone of polarizing activity and normalizes aberrant Gli3 repressor/Gli3 activator ratios observed in Gli3+/- embryos. Zic3 null;Gli3+/- neonates show rescue of the polydactylous phenotype seen in Gli3+/- animals. These studies identify a previously unrecognized role for Zic3 in regulating limb digit number via its modifying effect on Gli3 and Shh expression levels. Together, these results indicate that two Gli superfamily members that cause disparate human congenital malformation syndromes interact genetically and demonstrate the importance of Zic3 in regulating Shh pathway in developing limbs.
肢体异常是一种重要的出生缺陷，其遗传和机制尚不完全清楚。 hedgehog 信号转导的介质 GLI3 是肢体畸形的遗传原因，包括前轴和后轴多指、Pallister-Hall 综合征和 Greig 颅面多指并指综合征。与 GLI3 密切相关的 Gli（神经胶质瘤相关癌基因同源物）超家族成员 ZIC3 是人类 X 连锁异构性综合征的致病基因，但在肢体发育中尚未得到研究。在肢体发育过程中，GLI3 的翻译后加工从激活剂转变为抑制剂，拮抗并向后限制 Sonic hedgehog（Shh）的作用。我们证明 Zic3 和 Gli3 在发育中的肢体中表达重叠，并且 Zic3 在体外将 Gli3 从抑制剂转变为激活剂。在 Gli3 突变小鼠中，Zic3 功能丧失会消除前肢芽中的异位 Shh 表达，限制极化活性区的过表达，并使 Gli3+/-胚胎中观察到的异常 Gli3 抑制剂/Gli3 激活剂比值正常化。Zic3 缺失；Gli3+/- 新生鼠显示出 Gli3+/- 动物中所见的多指表型的挽救。这些研究确定了 Zic3 通过其对 Gli3 和 Shh 表达水平的修饰作用，在调节肢体指（趾）数方面的以前未被认识到的作用。总之，这些结果表明，两种导致不同人类先天性畸形综合征的 Gli 超家族成员在遗传上相互作用，并证明了 Zic3 在调节发育中肢体 Shh 通路中的重要性。
