Estudio del papel de la vía Wnt-PCP en el cierre del tubo neural a nivel caudal

Abstract

The last stage of neural tube (NT) formation involves closure of the caudal neural plate (NP), an embryonic structure formed by neuromesodermal progenitors and newly differentiated cells that becomes incorporated into the NT. Here, we show in mouse that, as cell specification progresses, neuromesodermal progenitors and their progeny undergo significant changes in shape prior to their incorporation into the NT. The caudo-rostral progression towards differentiation is coupled to a gradual reliance on a unique combination of complex mechanisms that drive tissue folding, involving pulses of apical actomyosin contraction and planar polarised cell rearrangements, all of which are regulated by the Wnt-PCP pathway. Indeed, when this pathway is disrupted, either chemically or genetically, the polarisation and morphology of cells within the entire caudal NP is disturbed, producing delays in NT closure. The most severe disruptions of this pathway prevent caudal NT closure and result in spina bifida. In addition, a decrease in Vangl2 gene dosage also appears to promote more rapid progression towards a neural fate, but not the specification of more neural cells. The Vangl2 mutation in mouse also show morphological alterations during the neural tube closure, displaying a flexion in neural folds preventing their fusion, forming cellular aggregates that were the cause of an abnormal migration of NCCs. The frequency of these aggregates in Vangl2+/Lp was increased in double mutants for Wnt-PCP signaling pathway, as well as in mutants of wound healing process, together with Vangl2. This points out the importance of actin filaments polymerization and cytoskeleton reorganization in neural tube closure and cellular aggregate formation. Finally, these cellular aggregates could form a tumor, similar to a lipoma primordium that appears in lipomyelomeningocele (LMMC) in humans. The strong genetic and functional evidence of the role of Vangl2 in NTD development in Vangl2+/Lp mouse mutant leads us to evaluate the possible implication of VANGL2 in the appearance of NTD in humans. By analyzing the coding sequence of VANGL2 three silent mutations were found. The study of this regulatory zone showed two unidentified variants, exclusive of patients, which appeared in heterozygosis in 1/58 and in 3/58 of patients with LMMC, the latter being a novel variant.