Tesis Doctorado
Expressión and functión of syndecan-4 during mouse development
Autor
Escobedo-Marambio, Noelia Andrea
Institución
Resumen
Neurulation is an essential process during early embryogenesis that results in theformation of the neural tube, the precursor of the brain and spinal cord. Neurulation includes neural fold elevation and bending, and adhesion and fusion of the neural folds. Disruptions that modizy the union of the neural fold in any of these steps could prevent neural tubeclosure. Neurulation has long been of interest in order to understand the origin of neural tube defects (NTDs) because, NTDs, including spine bifida, are one of the most prevalent (around 1/1000 births) and severe congenital malformations among human pregnancies.The initial step on neural tube closure is shaping of the neural plate, a process driven by convergent extension movements and regulated by components ofthe Non-canonical Wnt pathway, particularly of the Planar Cell Polarity (PCP) branch. Wnt/PCP describes the polarization of cells perpendicular to their apical-basal axis and this pathway is regulated by agroup of core genes including Frizzled, Dishevelled, Vangl2/Strabismus, and the intracellular proteins Prickle and Diego, among others. Studies in Xenopus and mice embryos have demonstrated that alterations ofthe Wnt/PCP signaling pathway disrupt convergent extension movements of the mesoderm and neuroectoderm resulting in shorter and broader embryos,with an abnormal neural plate and defective neural tube closure.The first indication for a role of Wnt/PCP genes in mouse development carne from theanalysis of the Loop-tail (Lp) mouse which has a point mutation in Vang/2. The Lp mutant mouse provides a model for the most severe mutant NTDs, craniorachischisis, in which the brain and spinal cord remain open. In addition, analyses of mice mutants for Wnt/PCP core genes have revealed a growing list of new Wnt/PCP phenotypes such us convergence andextension of the Organ of Corti and orientation of stereociliary hair bundles in the sensory epithelia ofthe cochlea, among others.Previously, in our laboratory we have demonstrated that Xenopus Syndecan-4 (xSdc4), a cell-surface heparan sulfate proteoglycan and component of the extracellular matrix, is essential for convergent extension, neural tube closure and neural crest directed migration inXenopus embryos through a non-canonical Wnt mechanism (Matthews et al., 2008; Muñoz et al., 2006). These evidences, together with the fact that components of the Wnt/PCP pathway are involved in gastrulation and neurulation movements suggest a possible interaction betweenxSdc4 and components of the Wnt/PCP pathway. In this thesis we have evaluated the expression and function of Syndecan-4 (Sdc4) and its relation with the Wnt/PCP pathway during mouse development. Importantly, no role for Sdc4 during mouse development has been described before.Here, we have found that Sdc4 has a widespread expression pattern in many tissues including those that requires Wnt/PCP pathway and overlapped temporally and spatially with Vangl2 and Frizzled-3 in the neural tube and neural folds. The cochlea phenotype in Sdc4-/embryosshows an asymmetry in the hair cells of the organ of Corti and additional sensoryhair cells outside of the sensory epithelia, a classical Wnt/PCP phenotype. The introduction of a heterozygous mutation of a Wnt/PCP gene, Vangl2, in the Sdc4 homozygous mutant resulted in abnormalities characteristic of Wnt/PCP mutants such as neural tube closuredefects, disorientation of stereociliary hair bundles and disorganization of cell-cell contacts in the cochlea and in vivo defective wound healing. Moreover, we have found that Vangl2 regulate Sdc4 levels in the surface of non-neuronal ectoderm in the closing neural tube and otic vesicle. Additionally, other proteoglycans member family (Syndecan -1 and -3) were upxviregulated in Sdc4-/- mouse embryonic fibroblast suggesting redundancy between syndecans in Sdc4 null mice.Our results strongly suggest that Sdc4 is as a new player of Wnt/PCP pathwayunveiling its importance during neural tube closure in mammalian embryos and providing a novel genetic tool to help to understand the function ofthe Wnt/PCP pathway.In addition, this study will contribute to understand the precise molecular role of the extracellular matrix in predisposing NTD. PFCHA-Becas Doctor en Ciencias Mención en Biología Celular y Molecular 167p. PFCHA-Becas TERMINADA