Cell Types and Cell Type Origination

Abstract.  Cell types are the fundamental building blocks of multicellular organisms. The number of cell types in an organism scales with an intuitive notion of organismal complexity, where the anatomically simplest metazoan has at least around five cell types while humans have 500 and most likely more different cell types. Understanding the evolutionary origin of novel cell types is fundamental for understanding the evolution of organismal complexity. Never the less, the study of cell type evolution is facing far-reaching conceptual and technical difficulties that we want to address is a small working group of experts from cell biology, systems biology and evolutionary biology. These problems can be summarized in the question: “what is a cell type?” How do we know when we identify a different cell type rather than a modification of an existing cell type? Is there a mechanistic difference between different cell states and different cell types? How do novel cell types originate in evolution? All these questions, however, are subsidiary to the first, namely whether “cell type” is a scientifically meaningful concept. This is the focus of the proposed working group.