Pan Haichun, Zhang Honghao, Abraham Ponnu, Komatsu Yoshihiro, Lyons Karen, Kaartinen Vesa, Mishina Yuji
Department of Biologic & Materials Sciences, School of Dentistry, University of Michigan, 1011 N. University Ave., Ann Arbor, MI 48109, USA.
Department of Biologic & Materials Sciences, School of Dentistry, University of Michigan, 1011 N. University Ave., Ann Arbor, MI 48109, USA; Department of Pediatrics, The University of Texas Medical School at Houston, Houston, TX, USA.
Dev Biol. 2017 Sep 1;429(1):260-270. doi: 10.1016/j.ydbio.2017.06.020. Epub 2017 Jun 19.
Craniosynostosis is caused by premature fusion of one or more sutures in an infant skull, resulting in abnormal facial features. The molecular and cellular mechanisms by which genetic mutations cause craniosynostosis are incompletely characterized, and many of the causative genes for diverse types of syndromic craniosynostosis have not yet been identified. We previously demonstrated that augmentation of BMP signaling mediated by a constitutively active BMP type IA receptor (ca-BmpR1A) in neural crest cells (ca1A hereafter) causes craniosynostosis and superimposition of heterozygous null mutation of Bmpr1a rescues premature suture fusion (ca1A;1aH hereafter). In this study, we superimposed heterozygous null mutations of the other two BMP type I receptors, Bmpr1b and Acvr1 (ca1A;1bH and ca1A;AcH respectively hereafter) to further dissect involvement of BMP-Smad signaling. Unlike caA1;1aH, ca1A;1bH and ca1A;AcH did not restore the craniosynostosis phenotypes. In our in vivo study, Smad-dependent BMP signaling was decreased to normal levels in mut;1aH mice. However, BMP receptor-regulated Smads (R-Smads; pSmad1/5/9 hereafter) levels were comparable between ca1A, ca1A;1bH and ca1A;AcH mice, and elevated compared to control mice. Bmpr1a, Bmpr1b and Acvr1 null cells were used to examine potential mechanisms underlying the differences in ability of heterozygosity for Bmpr1a vs. Bmpr1b or Acvr1 to rescue the mut phenotype. pSmad1/5/9 level was undetectable in Bmpr1a homozygous null cells while pSmad1/5/9 levels did not decrease in Bmpr1b or Acvr1 homozygous null cells. Taken together, our study indicates that different levels of expression and subsequent activation of Smad signaling differentially contribute each BMP type I receptor to BMP-Smad signaling and craniofacial development. These results also suggest differential involvement of each type 1 receptor in pathogenesis of syndromic craniosynostoses.
颅缝早闭是由婴儿颅骨中一条或多条缝线过早融合引起的，导致面部特征异常。基因突变导致颅缝早闭的分子和细胞机制尚未完全明确，多种综合征性颅缝早闭的致病基因许多尚未被鉴定出来。我们之前证明，神经嵴细胞中由组成型活性骨形态发生蛋白（BMP）IA型受体（以下简称ca-BmpR1A）介导的BMP信号增强会导致颅缝早闭，而Bmpr1a杂合无效突变的叠加可挽救过早的缝线融合（以下简称ca1A;1aH）。在本研究中，我们叠加了另外两种BMP I型受体Bmpr1b和Acvr1的杂合无效突变（以下分别简称ca1A;1bH和ca1A;AcH），以进一步剖析BMP-Smad信号通路的参与情况。与caA1;1aH不同，ca1A;1bH和ca1A;AcH并未恢复颅缝早闭表型。在我们的体内研究中，mut;1aH小鼠中依赖Smad的BMP信号降低至正常水平。然而，ca1A、ca1A;1bH和ca1A;AcH小鼠之间BMP受体调节的Smads（R-Smads；以下简称pSmad1/5/9）水平相当，且与对照小鼠相比有所升高。使用Bmpr1a、Bmpr1b和Acvr1无效细胞来研究Bmpr1a与Bmpr1b或Acvr1杂合性挽救mut表型能力差异的潜在机制。在Bmpr1a纯合无效细胞中检测不到pSmad1/5/9水平，而在Bmpr1b或Acvr1纯合无效细胞中pSmad1/5/9水平并未降低。综上所述，我们的研究表明，Smad信号通路不同水平的表达和随后的激活对每种BMP I型受体在BMP-Smad信号通路和颅面发育中的作用有不同贡献。这些结果还表明每种1型受体在综合征性颅缝早闭发病机制中的不同参与情况。
