β1 Integrin regulates convergent extension in mouse notogenesis, ensures notochord integrity and the morphogenesis of vertebrae and intervertebral discs

The notochord drives longitudinal growth of the body axis by convergent extension, a highly conserved developmental process that depends on non-canonical Wnt/planar cell polarity (PCP) signaling. However, the role of cell-matrix interactions mediated by integrins in the development of the notochord is unclear. We developed transgenic Cre mice, in which the beta 1 integrin gene (Itgb1) is ablated at E8.0 in the notochord only or in the notochord and tail bud. These Itgb1 conditional mutants display misaligned, malformed vertebral bodies, hemi-vertebrae and truncated tails. From early somite stages, the notochord was interrupted and displaced in these mutants. Convergent extension of the notochord was impaired with defective cell movement. Treatment of E7.25 wild-type embryos with anti-beta 1 integrin blocking antibodies, to target node pit cells, disrupted asymmetric localization of VANGL2. Our study implicates pivotal roles of beta 1 integrin for the establishment of PCP and convergent extension of the developing notochord, its structural integrity and positioning, thereby ensuring development of the nucleus pulposus and the proper alignment of vertebral bodies and intervertebral discs. Failure of this control may contribute to human congenital spine malformations.