Virginia Panara: The elephant in the cell: A multifaceted undertaking to uncover the molecular principles behind lymphatic endothelial cell identity

Abstract

The lymphatic vascular network is composed of a series of blind ended vessels, and is involved in physiological functions such as fluid homeostasis, lipid metabolism and immune trafficking. 

Despite lymphatic endothelial cells being derived from multiple organs, they share common molecular denominators, including the expression of the transcription factor Prox1. However, many of the molecular mechanisms involved in the acquisition and maintenance of lymphatic identity remains to be uncovered.

The aim of my thesis is to investigate how transcription factors and chromatin re-arrangements are involved in the acquisition and maintenance of lymphatic identity. In Paper I, the role of the transcription factor mafbb and its ability to partially compensate for the loss of its paralog mafba is investigated, leading to the description of topologically distinct requitements for LECs development in zebrafish. In Paper II, an evolutionary conserved prox1a enhancer is shown to be necessary for correct lymphangiogenesis in mouse, and its ablation is shown to cause the transition of LECs to hematopoietic-like cells. In Paper III, the effects of partial and total prox1 loss in zebrafish are investigated from a transcriptomic and epigenetic perspective, revealing an important role for prox1 in establishing LEC identity by suppressing genes associated with VEC fate. In Paper IV, the cis-regulatory landscape of prox1a is characterised identifying a number of lymphatic enhancers driving expression in either all LECs in the embryo or in anatomically distinct subsets of lymphatic vasculature. Finally, in Paper V, the chromatin organisation signature of LECs is explored, finding new candidate genes and enhancers active in the lymphatic endothelium.

In summary, my doctoral studies investigated the different levels of regulation of cell identity involved in LECs differentiation. My work focused on chromatin organisation, enhancer activity, transcription factors and differential gene expression to uncover the complex interactions between these separate mechanisms.