Classifying Cells and Cell Types

How do we describe the types of cells that comprise the human body? Pick any textbook of human biology and you'll find that cells are generally described as belonging to one of four types of tissue (nervous, muscle, connective, and epithelial) based on their broad function. At the next level of complexity, cells within a tissue are further described by their location and more specialized function (smooth muscle surrounding blood vessels; skeletal muscle attached to bones; cardiac muscle in the heart). Beyond these rather broad descriptions, many subtleties between cells are probably lost for lack of a way to measure or define them.

Some scientists think there may be a better way to identify and categorize cells. That's because what actually determines the differences between cells, both in terms of form and function, is the different proteins that they express. Those proteins are determined by the molecules of RNA that are present within the cell, which in turn are determined by which of the cell's genes are active. So to get a more refined measure of a cell's type and its true activity, it would make sense to measure not its shape, its location, or its broad function, but instead to determine which RNA molecules are present in the cell.

A group of enterprising scientists is attempting to do just that, according to an article in The New York Times. They've started with an organism (a type of worm) that has fewer than 1,000 cells. If all goes well, some day we may know a lot more about the incredible complexity of our various cells. And we may have to rethink how we classify cells and describe the relationships between them.