Resumen de Role of the transcriptional cofactors vestigial-like protein 4 (VGLL4) and yes-associated protein 1 (YAP1) in zebrafish morphogenesis
Morphogenesis is, largely, an embryonic developmental process through which individual cells, tissues and organs acquire a specific size and shape that as whole conform the outline of a given organism. Morphogenetic rearrangements take place in basically all embryonic tissues, although to a different extent and in distinct scenarios. Despite this diversity, the underlying mechanisms involve biochemical inputs and mechanical forces, which are applied at the single cell level, but result in coordinated robust, large-scale, spatio-temporal patterns at the tissue or organ scale. Understanding how these integrated patterns co-ordinately arise to originate a viable organism is one of the still unresolved issues in developmental biology.
This thesis has been designed with the overarching goal of investigating the molecular basis of these integrated patterns during embryonic morphogenesis, using the zebrafish as a model system. In particular, we have addressed whether and how VGLL4, a co-transcriptional factor, contributes to three critical morphogenetic events: epiboly, anterior-posterior axis elongation and eye cup formation. The rationale for this study relays on the notion that VGLL4 seems to act as competitor of YAP1, one of the most studied mechano-transducer proteins.
Taking advantage of CRISPR-Cas9 technology, we have first generated single and compound zebrafish vgll4 mutant lines for the three existing zebrafish paralogues: vgll4a, vgll4b and vgll4l. Using a battery of molecular, cellular and imaging approaches, we show that the maternal component of vgll4a is required for timely and coherent epibolic movements during gastrulation. vgll4a controls proper E-cadherin/β-catenin distribution at the blastomere plasma membrane upstream of Yap1 activation, indicating that vgll4a supports, rather than antagonise, Yap1 signalling, at least in this context. We further show that the zygotic form of a different vgll4 paralogue, vgll4b, is a novel piece of the gene regulatory network that controls anterior-posterior axis elongation. Its function seems required within committed mesodermal progenitors, likely by repressing tbx16 activity, which, in turn, supports the development of the somitic mesoderm. Finally, we provide evidence that Yap1 is required to maintain RPE integrity during optic cup morphogenesis, whereas vgll4 paralogues could down-regulate proliferation of the retinal neuroepithelium.
Taken together, these data provided novel information on embryonic morphogenesis, showing different and context dependent functions for vgll4, which are dependent or independent from Yap1 activity. From a broader perspective our results may impact on our understanding of congenital malformations or pathological conditions such as primary or metastatic tumours, given the known implication of yap1 and vgll4 in these conditions.
