In the vertebrate body each tissue/organ acquires three-dimensional (3D) structure during embryonic development and becomes aligned relative to other tissues/organs to generate the global body shape. The existence of a gene essential for orchestrating the complex process of building 3D body shape has not previously been suspected.Understanding the mechanisms by which 3D organs are built and organised isessential for the advancement of regenerative medicine, which aims to facilitate 3Dtissue/organ formation and integrate these transplanted tissues/organs in the proper3D alignment within the host to allow their full functionality. A large-scale ENUmutagenesis screen in medaka (Oryzias latipes) identified the hirame (hir) mutantwhere the morphogenesis of epithelial tissues is affected causing a flattened body inwhich individual organs/tissues collapse and are misaligned. The hir mutant alsoexhibits cell migration defects of the primary blood vessels and the heart. hir is arecessive lethal mutation with full penetrance and a robust phenotype. Positionalcloning showed the unique hir phenotype is caused by a point mutation in the region ofthe Yes-associated protein (YAP) gene that encodes the WW1 protein domain of YAP.This mutant can therefore serve as a useful tool for the study of how 3D tissues andorgans are generated and how they align to give rise to the global body shape.This work details how the combined use of medaka and zebrafish (Danio rerio)allowed the identification of YAP as essential for shaping the vertebrate body and itsbiophysical properties. In this thesis, it is reported for the first time that YAP is essentialfor the fundamental process of organogenesis at the whole-body scale. Analysis ofYAP function in intact mutant animals by a variety of means including time-lapseconfocal microscopy and intricate cell-transplantation experiments reveals a previouslyunrecognised but pivotal role for YAP. YAP governs various cell behaviours includingoriented division and cell stacking to generate 3D tissues with proper tissue tension. Inturn this tissue tension mediates extracellular matrix assembly and integrin signalling,which allows the correct alignment of adjacent tissues to produce functional organsthat undergo coordinated morphogenesis to produce the overall 3D body shape.Furthermore, it is shown that these two major functions of YAP are mediated byactomyosin-dependent tension as demonstrated by in vivo force measurements.
|Date of Award||7 Feb 2014|
|Supervisor||Makoto Furutani-Seiki (Supervisor) & Robert Kelsh (Supervisor)|