Multinuclear and Mononuclear Polyploidy in the Drosophila Hindgut and Heart

Abstract

<p>A fundamental question of biology is how tissues are organized. Tissues can be composed of many small cells or comparatively fewer large cells that add nuclear content to facilitate tissue growth. The cells can be separate, discrete units or interconnected collectives. The nuclear composition of a tissue has functional consequences from the tissue physiology to likelihood of cancers and hyperproliferation to the response to stress and tissue damage. These two decisions, to be small or large and to be distinct (mononucleated) or joined (multinucleated), and, especially, the interaction between these choices are poorly understood. In this dissertation, I identify the Drosophila rectal papillae as a new model to study tissue interconnectivity, multinuclearity, and the interaction between nuclear content and cytoplasm-sharing. I played a major role in the discovery that the adult Drosophila rectal papillae share cytoplasm and proteins up to at least 62 kDa. This sharing is developmentally regulated and requires membrane trafficking and gap junction genes instead of canonical cell-cell fusion or incomplete cytokinesis factors. This mechanism of sharing does not appear to involve plasma membrane breaches, a novel way for tissues to share contents. Additionally, I advance the Drosophila larval heart as a model to study nuclear content (ploidy) in heart development and physiology. Together, my work explores how tissues use mononucleate and multinucleate ploidy in development and physiology.</p>