Ramanathan Lab

A striking increase in cellular size heterogeneity is a salient feature of both organ development and cancer progression. Our goal is to discover the principles that underpin how cells with divergent sizes pack into epithelial tissue and how alterations in cellular packing influence tissue homeostasis. The shape and size of individual components dictate the morphology and integrity of any structure. Indeed, the regulation of cell shape through the modulation of cellular mechanical properties is a key factor in tissue morphogenesis. However, in contrast to shape, the role of cell size in determining the form of epithelial tissues is largely unknown (Fig. 1). To determine the role of cell size in tissue packing, we ask the following fundamental questions: 1) How do cells of diverse sizes pack and maintain stereotypical organization in healthy epithelial tissues, and 2) What are the implications of packing cells with ectopic sizes in the context of epithelial diseases. These overarching questions will be addressed in the following two projects.

Project 1: Determine how the large Paneth cells and small Lgr5⁺ stem cells at the base of the intestinal crypt domain maintain a checkerboard-like order. 
How animal cells of diverse shapes and sizes pack to form functional tissue is a fundamental biological question. Nevertheless, the current understanding of how tissues organize is mostly from examining the adhesive and tensile properties of similarly shaped cells. Previously, we discovered that discrepancies in cell size induce cell junctions to rearrange and cause stereotypical cellular reorganization. In our laboratory, we will dissect the principles of how, despite the rapid turnover, a checkerboard-like arrangement is maintained by the intestinal stem and support cells (Fig. 2).

Project 2: The tissue-level consequences of shifting the nuclear-cytoplasm volume ratio of uniform enterocytes in the intestinal villus.
Although cells of the same type have remarkably uniform morphology, tumor cells are typically pleomorphic and can exhibit abnormal variations in the size of cells and nuclei. Nevertheless, the influence of such variance in disease progression is not well understood. Furthermore, the tight correlation between the cell and nuclear size is frequently perturbed in diseases; but what are the pathological implications of this decoupling? Previously, we showed that abnormality in cellular size can have a profound impact on how cell pack and tissue organize. In our laboratory, we will determine how the organization of small intestinal villi in mice can be altered by abnormal cell and nuclear shape (Fig. 3).Our approach to addressing these questions is highly interdisciplinary. We integrate confocal imaging with biophysics and sophisticated genetic manipulation to quantitatively distinguish the influence of cell mechanics, shape, and size in tissue packing and homeostasis. We leverage a wide range of models including traditional 2D culture, 3D organoids, and mouse intestinal tissue.  Over the long term, we anticipate that our study will extend the understanding of how cells self-assemble into tissues with stereotypical forms and reveal how functional tissue architecture is perturbed in disease.