Cellular and Molecular Life Sciences

, Volume 71, Issue 11, pp 2149–2164 | Cite as

Combinatorial activity of Six1-2-4 genes in cephalic neural crest cells controls craniofacial and brain development

  • Ricardo C. Garcez
  • Nicole M. Le Douarin
  • Sophie E. Creuzet
Research Article


The combinatorial expression of Hox genes is an evolutionarily ancient program underlying body axis patterning in all Bilateria. In the head, the neural crest (NC)––a vertebrate innovation that contributes to evolutionarily novel skeletal and neural features––develops as a structure free of Hox-gene expression. The activation of Hoxa2 in the Hox-free facial NC (FNC) leads to severe craniofacial and brain defects. Here, we show that this condition unveils the requirement of three Six genes, Six1, Six2, and Six4, for brain development and morphogenesis of the maxillo-mandibular and nasofrontal skeleton. Inactivation of each of these Six genes in FNC generates diverse brain defects, ranging from plexus agenesis to mild or severe holoprosencephaly, and entails facial hypoplasia or truncation of the craniofacial skeleton. The triple silencing of these genes reveals their complementary role in face and brain morphogenesis. Furthermore, we show that the perturbation of the intrinsic genetic FNC program, by either Hoxa2 expression or Six gene inactivation, affects Bmp signaling through the downregulation of Bmp antagonists in the FNC cells. When upregulated in the FNC, Bmp antagonists suppress the adverse skeletal and cerebral effects of Hoxa2 expression. These results demonstrate that the combinatorial expression of Six1, Six2, and Six4 is required for the molecular programs governing craniofacial and cerebral development. These genes are crucial for the signaling system of FNC origin, which regulates normal growth and patterning of the cephalic neuroepithelium. Our results strongly suggest that several congenital craniofacial and cerebral malformations could be attributed to Six genes’ misregulation.


Neural crest Hoxa2 Signaling Head skeleton Holoprosencephaly Electroporation RNAi 

Supplementary material

18_2013_1477_MOESM1_ESM.pdf (306 kb)
Supplementary material 1 (PDF 305 kb)


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Copyright information

© Springer Basel 2013

Authors and Affiliations

  • Ricardo C. Garcez
    • 1
    • 3
  • Nicole M. Le Douarin
    • 2
  • Sophie E. Creuzet
    • 1
  1. 1.Institut de Neurobiologie, Laboratoire Neurobiologie et DéveloppementCNRS-UPR3294Gif-sur-YvetteFrance
  2. 2.Académie des SciencesParisFrance
  3. 3.Centro de Ciências BiológicasUniversidade Federal de Santa CatarinaFlorianópolisBrazil

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